Valvular disease is a frequent cardiac pathology leading to heart failure and, ultimately, death. Mitral regurgitation, defined as the inability of the two mitral leaflets to coapt, is a common valvular disease and a self sustained pathology. A better understanding of the mitral valve histological layers provides a better understanding of the leaflet and chordae changes in mitral valve prolapse.
Mitral valve prolapse may occur in myxomatous degenerative abnormalities, connective tissue disorders or in sporadic isolated cases. It is the most common mitral abnormality of non-ischemic cause leading to severe surgery-requiring mitral regurgitation. In addition to standard echocardiographic investigations, newly implemented three-dimensional techniques are being used and they permit a better visualisation, from the so-called ‘surgical view’, and an improved evaluation of the mitral valve.
Hypertrophic cardiomyopathy is the most frequent inherited myocardial disease caused by mutations in various genes encoding proteins of the cardiac sarcomere, leading to a marked left ventricular hypertrophy unexplained by other comorbidities. The pathological echocardiographic hallmarks of hypertrophic cardiomyopathy are left ventricular hypertrophy, left ventricular outflow tract obstruction and systolic anterior motion of the mitral valve. The systolic anterior motion of the mitral valve contributes to the development of mitral regurgitation and further narrows the left ventricular outflow tract, leading to more severe symptomatology. Cardiac magnetic resonance imaging accurately measures the left ventricular mass, the degree of diastolic function and it may also be used to distinguish phenotypic variants.
The clinical outcome of patients with these pathologies is mostly determined by the selected option of treatment. The purpose of surgical correction regarding mitral valve involvement is to restore valvular competence. Surgery has proven to be the only useful treatment in preventing heart failure, improving symptomatology and reducing mortality. Our approach wishes to enhance the understanding of the mitral valve’s involvement in hypertrophic cardiomyopathy and mitral valve prolapse from genetic, haemodynamic and clinical perspectives, as well as to present novelties in the grand field of treatment. IntroductionMitral valve structure and haemodynamicsGenetic causesLeaflet elongation and thickeningDiagnosis 5.1 Mitral valve prolapse 5.2 Mitral valve in HCMTreatment6.1 Mitral Valve Prolapse Management6.2 Management of mitral valve in HCM6.3 Clinical outcome6.4 Future perspectives Conclusions1The prevalence of valvular heart disease was reported to be 2.5% in 2015, in the USA alone1, with no difference in frequency between genders.2 The prevalence rises with age, affecting mostly people older than 65 years of age. The most frequent entities are aortic stenosis and mitral regurgitation (MR).3Valvular disease is a frequent cardiac pathology worldwide, which ultimately may lead to heart failure. The incidence of valvular disease in industrialized countries is increasing, as a result of the increase in general life expectancy.1 Other complications include arrhythmias such as atrial fibrillation (AF), endocarditis and death.4 The causes that lead to MR are classified as ischemic (due to the coronary insufficiency) and nonischemic. MR can also be classified as functional, due to annular dilation (as seen in dilated cardiomyopathies) or organic, in pathologies that affect the intrinsic structure of the valve, as seen in mitral valve prolapse (MVP).1 MR may also arise due to a congenital or an acquired pathological state.5MR is defined as the inability of the two mitral leaflets to coapt, leading to a systolic retrograde blood flow, from the left ventricle (LV) to the left atrium, which will result in volume overload of the left heart chambers and dilation of the mitral annulus. As a self-sustained pathology, it usually aggravates over time, leading to left heart failure.5,6 However, concurrent with ventricular remodeling, mitral leaflets can become inadequately small (as seen in dilated cardiomyopathies) or suffer a process of elongation. In hypertrophic cardiomyopathy (HCM), the leaflet elongation exceeds the needs of the reduced volume of the LV, further aggravating the left ventricular outflow tract (LVOT) obstruction and can predispose to systolic anterior motion (SAM) of the MV.5,7 In MVP, the leaflets are long and exhibit structural fibroelastic abnormalities.5,8Until now, the mitral valve (MV) was considered a passive structure. It has recently been demonstrated that it can react to the morphological changes that involve the LV and that it may also alter its structure irrespective of the state of the nearby structures.1The surgical treatment has an important role in the natural history of the disease and it has been proven to be the only treatment that may efficiently prevent heart failure, improving symptoms and reducing mortality by 70%. The best results were seen in asymptomatic MR, which supports the importance of an early and accurate diagnosis.This review highlights the mechanisms, the diagnosis and the current and future management of patients with mitral regurgitation, in the context of mitral valve prolapse and/or hypertrophic cardiomyopathy.9 The anterior leaflet is relatively fixed and its insertion occupies 1/3 of the circumference of the annulus, while the posterior one occupies the rest of the 2/3 and is more flexible, being the most susceptible to prolapse.9,10 Each of the leaflets is divided by two notches in three parts, called scallops, three anterior  and three posterior . This division is more evident in the posterior leaflet, and is an important aspect in the diagnosis and surgical treatment of MVP.10,11 The two leaflets are attached by their bases to the mitral annulus, whereas the edge and midportion of the leaflets are attached to the papillary muscles by means of the chordae tendineae. This system maintains an unidirectional blood flow during diastole, from the atrium to the ventricle and closes completely, preventing retrograde flow from the ventricle to the atrium, during systole.1,5The mitral apparatus is composed of two leaflets, the anterior and the posterior one respectively, the mitral annulus, and the subvalvular complex, which is composed by the papillary muscles and the chordae tendineae. Each of these structures has an important role in maintaining the function of the valve.5,12, dense collagen fibers, fibroblasts and glycosaminoglycans that easily absorb water and disperse mechanical stress when the two leaflets coapt.5,13 The chordae tendineae are strong structures with viscoelastic properties, which are composed of a core of collagen and a sheet of elastin.5 Due to the presence of the atrial smooth muscle fibers both on the annulus and the basal portion of the leaflet, the annulus will contract during presystole, further helping coaptation of the leaflets. It has been shown that the contraction of the annulus can be activated through ventricular smooth muscle fibers as well, although in this case MR may occur.14Histologically, it has been shown that the leaflets comprise, from the annulus to the edge, smooth muscle fibers, nerve fibersatrialis , spongiosa  and ventricularis .4,5 These components are modified in diseases such as MVP.15 On both sides, the leaflets are covered with a thin endothelial layer.4 Moreover, in the structure of the valve, there are valvular interstitial cells (VICs) that are connected through signaling pathways with the cells which compose the endothelial layers. When valve homeostasis is disrupted, myofibroblastic transition of the interstitial cells occurs, therefore promoting valve thickening.4,5,16In transverse sections, the valve is composed of three layers – 17,18The relative proportion of the valvular histological components varies with age, over time decreasing in cellularity and glycosaminoglycans, while increasing in fragmentation of the elastin network, collagen fibers and calcifications, thus promoting stiffness and loss of function of the valve.Mitral Valve Prolapse19MVP may occur in myxomatous degenerative abnormalities such as Barlow’s disease, connective tissue disorders such as Marfan’s Syndrome (MFS) and it may also be found in sporadic isolated cases.20-22 Autosomal dominant and X-linked forms have also been cited.19Through chromosomal mapping, it has been shown that myxomatous MVP has a genetic heterogeneity which implies mutations located on chromosomes 16, 11 and 13.23,24 Fibrillin-1 protein is the principal component of extracellular matrix (ECM) microfibrils and also one of the regulating factors of TGF-β activity, by inhibiting it.24 In patients with fibrillin deficiency, an enhanced activity of TGF-β was noticed. Also, in patients with TGF-β receptor 2 mutations, the altered receptor presented increased activity for its agonist.23,24Mutations of the fibrillin-1 (FBN1) gene which encodes the fibrillin-1 protein and mutations of the transforming growth factor β (TGF-β) receptor 2 gene are responsible for the occurrence of Marfan’s syndrome, as well as MVP.24It has also been shown that cells from valves with FBN1 mutations presented decreased apoptosis rates and increased cell proliferation.24,25 Filamin-A is an actin-binding protein, involved in maintaining membrane stability and sheltering cells against injury and also has the function to positively regulate the expression of TGF-β.24Another gene implicated in the etiopathogenesis of MVP is the Filamin A gene. An association between the up-regulation of Filamin A gene and X-linked forms of myxomatous valvulopathies has been shown.24An up-regulation of TGF-β – inducible gene H3, has also been found in myxomatous degenerated valves, which supports the theory that increased levels of this factor contribute to the cause of MVP. Moreover, high levels of TGF-β have also been found in the mitral valves of patients with isolated myxomatous MVP.26Another potential gene incriminated as one of the causes of MVP is the Dachsous Cadherin-Related 1 (DCHS1) gene. There is evidence that down-regulation of this gene determines abnormal valvular development, with structural valvular changes, as seen in MVP, with family aggregation and mostly involvement of the posterior leaflet.Hypertrophic Cardiomyopathy27 characterized by high grade left ventricular hypertrophy (LVH) which cannot be explained by other comorbidities (such as heightened afterload or restrictive diseases).28,29HCM is the most frequent inherited cardiomyopathy30, caused by mutations of the proteins that make up the sarcomere, in contrast to dilated cardiomiopathies, where mutations of cytoskeletal proteins are incriminated.HCM is an autosomal dominant disease30 The most frequently occurring mutations associated with HCM are found in cardiac myosin-binding protein C 3 (MYBPC3) gene, cardiac muscle β-myosin heavy chain 7 (MYH7) gene and troponin T protein type 2 (TNNT2) gene.30-32 Mutations of genes encoding cytoskeletal proteins may also be involved in the etiology of HCM.27 All of the above support the idea of a heterogenic etiology and phenotypic appearance of HCM.Until recently, it has been considered that mutations in 8 genes that codify the sarcomeric proteins are responsible for HCM, but it has been proven that up to 43 altered genes may modify the structure of myocites, further being involved in the etiology of this disease.30 It has been shown that some mutations predispose to an enhanced calcium sensitivity, which can lead to metabolic impairment and cytotoxicity.27 Heightened oxidative stress and altered expression levels of SERCA and phospholamban have also been cited in the pathology of HCM.33,34 Also it has been shown that mutations in the cardiac ryanodine receptor (mainly implicated in the genesis of arrhythmias) may be correlated with HCM, mostly with symmetric apical forms.30These mutations can interact at three main levels: sarcomeric function, metabolic pathways and calcium signaling pathways.27,30 Sporadic cases of HCM may also appear and are explained by a novel mutation or incomplete gene penetrance in the patient’s parents.30In up to 5% of cases HCM can be accompanied by skeletal muscle disorders, such as neuromuscular diseases.Mitral valve prolapse35,36 Both of these degenerative processes are associated with leaflet elongation and thickening, as well as chordal abnormalities.8,37MVP presents two main phenotypes that are recognized in the literature: myxomatous degeneration – Barlow’s disease and fibroelastic dysplasia.38 Members of the TGF-β family are implicated in mediating signals in the cardiac cushion. These reciprocal signals between the endocardial and myocardial cell layers promote the transformation of valvular endothelial cells (VECs) into (VICs).39 It has been shown, both on animal models40 and in human in vitro studies that TGF-β up-regulation plays an essential role in the pathogenesis of MVP. TGF-β activates VICs towards a myofibroblast-like phenotype and causes excessive remodeling of the ECM.41,42Heart valve development may help understand signaling pathways involved in MVP. Primordial valves derive from the cardiac cushions which are regional swellings of the ECM.38,43 VICs modify their phenotype to myofibroblast-like cells characterised by the expression of vimentin and α-smooth muscle actin and lack of expression of myosin heavy chain isoforms 1 or 2- markers of differentiated smooth muscle cells.44,45 Normal VICs are responsible for maintaining a tight balance between degradation and synthesis of the ECM proteins by means of enzymes such as matrix metalloproteinases (MMPs) - collagenase and gelatinases, as well as tissue inhibitors of MMPs.8,37 In contrast, modified VICs are responsible for an exceedingly high rate of collagen and elastin degradation compared to the production rate due to increased concentrations of various proteolytic enzymes.45-47 Furthermore, possible fibrocytes capable of differentiating into myofibroblasts that both produce and degrade collagen and elastin, may be present in myxomatous valves.38In myxomatous degeneration, the disruption of the ECM homeostasis is an essential mediator of the pathological changes.spongiosa.43,48 These muccoplysaccharides overflow onto ventricularis collagenous fibers and atrialis elastic fibers resulting in reduction of the collagen fibers and altered architecture of the leaflet. Nevertheless, there is an increase in type III collagen to the detriment of type I which is more resistant to traction.43,48 These changes promote valve thickening. The chordae undergo changes which reside in mucoid infiltration with glycosaminoglycans leading to the disrupture of their fibrous core.43,49 Grande-Allen et al. concluded that the predominant glycosamino-glycans in which the chordae are abundant are chondroitin/dermatan 6-sulfate, in contrast to leaflets which contained predominantly hyaluronan.49 These findings may account for both chordal and leaflet reduced tensile strength.50The excessive degradation of the ECM results in an extracellular accumulation of mucopolysaccharides which leads to the augmentation of the 51 The posterior superimposed fibrous tissue has been proven to be the main cause of posterior leaflet thickening rather than the expansion of the spongiosa. Furthermore, it is thought to be the result of the abnormal contact between leaflets and chordae.52There is evidence showing that non-ruptured choardae tendinae may be hidden (be covered up) by superimposed fibrous tissue of the leaflets, thus partaking to their thickening. Nevertheless, ruptured chordae may be partially included in the posterior superimposed fibrous tissue of the leaflets.36 Although the leaflets present as thin and smooth and the chordae slightly elongated, thickened lesions have been noticed in the leaflet segments exposed to MR.8,36 Thus, isolated regions of the leaflets are pathologically involved.35,36 This leads to the hypothesis that the thickened lesions are secondary to MR.8In fibroelastic dysplasia, there is a decrease in connective tissue which is deficient in collagen, elastin, and proteoglycans.Hypertrophic cardiomyopathyThere is an ongoing discussion regarding the pattern of geometrical changes of the MV in HCM.53 SAM is caused by elongation of the anterior and/or posterior leaflet(s) predominantly along with anterior displacement of the papillary muscles that, with each contraction, come in contact with the septum further aggravating LV obstruction and conferring undue mobility to the mitral apparatus.5 It has been shown that LVH is a contributing but not necessary factor for left ventricular outflow tract obstruction (LVOTO). While the exact cause of the increase in size of the mitral leaflets is unknown, Patel et al. has shown that patients with infraclinical or with very little LVH can present LVOTO strictly in a phenotypic variant of HCM that affects anterior mitral leaflet length, attachment of the chordae tendineae and bifid papillary muscle mobility.54His work is supported by older papers that suggest a hemodinamically independent cause of mitral valve remodeling.55-57Thickening and elongation of the mitral leaflets are often encountered in HCM patients. Historically, abnormalities in HCM were thought to be limited to SAM. Recently it has been shown that this anomaly is not unique to HCM.58,59This is in contrast to the belief that changes to the mitral apparatus are strictly a consequence of ventricular remodeling and ventricular mass.From this data Albert A. Hagège et al. has grouped the current available research into hypotheses.A. The Genetic Hypothesis60,61 The presence of an enlarged leaflet in patients with HCM without hypertrophy or LVOTO suggests that changes in the geometry of the valve are not due to leaflet stress or ventricular remodeling, but rather depends solely on a genetic defect (a sarcomere gene mutation).A posterior leaflet elongation of >14mm was observed in carriers of a morbid HCM mutation, but without hypertrophy or obstruction.62As mentioned above, MYBPC3 mutations are one of the causes of HCM. A study performed by Judge et al. shows that MYBPC3 knock-out mice with ecocardiographically diagnosed LVH have long and thick MV leaflets compared to controls. This abnormality occurs in the absence of LVOTO or SAM.B. The Adaptive Hypothesis58,59 A study performed on animals suggests that these changes might arise through reactivation of developmental embryonic pathways through endothelial-mesenchymal trans-differentiation (EMT). Cells synthesize α-smooth muscle actin in the atrial endothelium increasing collagen deposition. These changes are seen in the papillary muscles and chordae tendineae.63-65 As Hagège et al. concurs, this does not explain why leaflet enlargement occurs in the absence of SAM.This is the theory that postulates that mechanical stress applied to the leaflets causes leaflet lengthening.C. The Concurrent Disease Hypothesis:55The possibility of an independent MV disease that occurs with HCM has been brought up, namely the association between MVP and HCM. This theory has gained little traction due to the extensive studies and excellent diagnostic methods of MVP.D. The Developmental hypothesis63This hypothesis is developed from the feature of adult valves of being susceptible to embryonic signals that were active during fetal valvulogenesis. During myxomatous degeneration EMT is gradually reactivated. A surgical model shows similar changes occurring when MR is due to leaflet stretch.66 It has been proposed that periostin is the stimulus which dictates the differentiation of EPDCs. When a sarcomeric gene mutation is present, EPDCs that have differentiated into cardiomyocytes become fibroblasts under the stimulus of periostin.67An explanation of the wide variance of phenotypic appearances of HCM has been postulated. Epicardial-derived cells (EPDCs) are normally found on the surface of the heart. Physiologically they differentiate into fibroblasts as they migrate into the ventricular and atrial walls and into cardiomyocytes as they migrate into the interventricular septum.66 It directly affects restructuring of the ECM inducing remodeling and mediating response to tissue damage.68Periostin is normally found in tissues derived from the mesenchyme, most commonly in osteoblasts, periosteum and the periodontal ligament. It is also involved in cancer development and the mesenchymal development of the heart.69,70Several other animal studies have shown increased levels of periostin in HCM mice and it has been consequently postulated that it may be implicated in valvular degeneration.Figure 1).71New studies also suggest that in mice with HCM, genes that encode mutated contractile proteins cause EPDCs derived cardiomyocytes to become fibroblasts. This process occurs under an elevated level of periostin which may prove that periostin is responsible for collagen deposition on the MV, which may ultimately result in elongated leaflets  systolic atrial displacement of at least 2 mm over the long-axis annular plane, that can be accompanied or not by leaflet thickening.35,73,74 The disease is characterised by typical fibromyxomatous changes of the leaflet tissue and possibly chordal abnormalities such as lengthening.37,73 According to the Framingham Heart Study, MVP affects approximately one in 40 individuals, irrespective of sex and age.75MVP is the most common mitral abnormality of non-ischemic cause leading to severe surgery-requiring mitral regurgitation.35,36Barlow's disease and fibroelastic dysplasia are the two different pathologies most commonly associated with MVP. Early presentation with multiscallop prolapse, diffuse thickening of the leaflets, lengthened chordae and severe annular enlargement is characteristic of Barlow's disease. Fibroelastic dysplasia, unlike Barlow's disease, presents later in life, involves isolated regions of the valve, rarely produces severe annular enlargement and frequently associates rupture of chordae.75,76 The early misconception that this syndrome frequently occurs simultaneously with MVP was not confirmed by case-control studies.35,74There is no specific symptomatology that characterises MVP. However, a constellation of symptoms  and clinical findings  has been associated with this pathology under the name of MVP syndrome.35,72Symptoms occur when the compensatory ventricular dilation is overwhelmed and they indicate severe MR and LV dysfunction. Nonetheless, if the ventricular compensation of the severe MR is appropriate, the patient may remain asymptomatic for many years. Exertional dyspnea and exercise intolerance follow exhaustion of compensatory mechanisms and irreversible LV dysfunction occurs, as well as chordal rupture and sudden onset of AF.72 As far as the progression of the asymptomatic MVP to severe MR is concerned, there is evidence showing that 25% of the asymptomatic patients tend to develop a significant clinical form over the course of 3 to 16 years.77The importance of diagnosing MR as well as establishing its severity, lays in the excellent chance of improved quality adjusted life years for patients, provided they undergo intervention before symptomatology onset or irreversible ventricular damage.74MVP is more likely to be found in people having thoracic skeletal abnormalities and a leaner build.76,78When asymptomatic, this disease is usually discovered incidentally during clinical examination or during an echocardiogram.75,79 Classically, a dynamic, mid-to-late systolic click commonly associated with a late systolic murmur has been described.74 However, a late systolic murmur is more frequent than a mid-to-late systolic click.79MVP is usually suspected following auscultatory findings, physical examination being a diagnostic standard.74,80The click-dynamics may be perceived with specific maneuvers: an earlier click is produced by a reduced end-diastolic volume , whereas opposite maneuvers generate a click shift into late systole.35With chordal rupture and consequent leaflet flail, the murmur becomes holosystolic. A flailing posterior leaflet will generate a murmur radiating anteriorly which may mimic aortic stenosis.74,80 Thus, although a thorough physical examination is highly sensitive for echocardiographically documented MVP, its specificity is limited.80False positive auscultatory findings – non-prolapse related systolic clicks may occur. There are multiple causes for these findings such as bicuspid aortic stenosis, atrial myxoma and pericarditis. Nevertheless, echocardiographically documented prolapse may exist without auscultatory click or murmur.73,81 Cardiac ultrasound provides information regarding valve morphology, severity of regurgitation, global and regional ventricular function and allows correlations between valve structure, biomechanics and haemodynamics.5,73 The standard investigations for patient assessment with MVP are two-dimensional (2D) and Doppler echocardiography.82,83 Newly implemented techniques of three-dimensional (3D) echocardiography, transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE), permit visualisation of the MV from the so-called ‘surgical view’ thus enabling a better evaluation of the MV apparatus for pre-operative assessment.73,81The primary diagnosis mean of MVP is echocardiography.Transthoracic echocardiography5,73 Additionally, leaflet displacement in relation to each other  leads to malcoaptation, augmenting the severity of the regurgitation.5 Taking into account the saddle shape of the mitral annulus, distinct terms are used to describe leaflet displacement, while asserting prolapse magnitude.1,5,84 Thus, billowing refers to moderate degree prolapse when leaflet tips remain in the ventricle, , while leaflet flail denotes severe prolapse when leaflet tip coaptation fails and both bodies and tips are displaced into the atrium.1,5MVP is echocardiographically defined as valve leaflet displacement over the parasternal or apical long-axis annular plane during systole of more than 2 mm.5,72 Other anatomical abnormalities that should be evaluated are the LV dimensions and function by means of measuring the ejection fraction and end-systolic and end-diastolic diameters and volumes.72Valve characteristics that are evaluated by echocardiography in MVP are leaflet thickness and length, mitral annulus diameter and calcification, as well as the severity of MR.5,51 and it has been proven echocardiographically via parasternal long-axis view in diastole that mid-leaflet thickness is increased in 40% of patients with severe forms of this disease.5,85Generally, leaflets are elongated and thickened in MVP82,83 Doppler quantitative methods are more useful for grading the severity of MR1,83 compared with jet-based assessment which has major limitations. Proximal isovelocity surface area (PISA) method has become the standard quantitative assessment of MR.1,86 PISA allows measurement of effective regurgitant orifice area (EROA), regurgitant volume (RVol) and regurgitant fraction (RF).1,81,83 Regurgitation is considered severe in the setting of MVP when EROA is at least 40 mm2, RVol is at least 60 ml per beat and RF is at least 50%1,81 .As mentioned, leaflet malcoaptation leads to MR. Establishing the severity of MR is highly important, as an intervention could be considered even in asymptomatic patients with severe MR in the presence of LV dysfunction.1 Ventricular dysfunction is diagnosed in the setting of severe MR due to MVP when the ejection fraction is less than 60% and the end-systolic diameter is higher than 45 mm.83LV dimensions can also be performed by means of TTE. Volume overload is indicated by end-diastolic and end-systolic LV diameters and volumes, while ventricular function is assessed by end-systolic LV dimensions and LV ejection fraction.The role of transesophageal echocardiography35,81,87 It is preferred when TTE imaging is of poor quality or when complex, calcified or endocarditic lesions are being assessed.1 This investigation is mainly used on inpatients and during interventions to evaluate lesions and to monitor surgical results88 .MVP imaging obtained via TEE is of higher quality compared to TTE, as it provides better assessment of the etiology and quantification of the severity of MR.The emerging role of three-dimensional echocardiography1,812D echocardiographical evaluation is complemented and its results are enhanced by 3D echocardiography, as the latter allows assessment of structures that might be problematic when using 2D echocardiography, such as the mitral annulus.81,89 3D multiplanar reconstruction (MPR) is a revolutionary echocardiography technique with an improved accuracy of MVP description compared to 2D investigations and the benefit of combining these two methods (3DMPR and 2DTTE) as part of the pre-operative investigations is increased.11,893D TTE provides accurate data regarding anatomic localisation of prolapsing scallops, allowing better spatial localisation of commissures and quantification of MR severity.81,87,90 . It has been shown that 3DTEE is comparable to cardiac magnetic resonance (CMR) regarding feasibility and accuracy of diagnosis.81,913D TEE is superior to and has a distinct advantage over 2D TEE because imaging of the MV apparatus is more detailed and allows a more accurate localisation of prolapsing scallops11,81,83,893D echocardiographic assessment of patients with MVP is now recommended for routine examination and its potential benefit is highlighted by current guidelines and studies.The main application of CMR insofar as MVP is concerned, is strictly for pre-surgical patient assessment.92Assessment of MR requires quantification of: grade of MR in order to determine the need for surgical intervention, the mechanism through which MR has appeared , LV volumes for surgical risk assessment and myocardial viability in ischemic MR. the two investigations were almost equally effective in diagnosing prolapsed or flailing leaflets with TEE actually proving slightly more effective in this regard.93,94In two studies comparing TEE and CMR 94Although semi-invasive and operator dependent, TEE is excellent at accurately preparing patients for surgery and monitoring patient’s surgical response. CMR for MVP may be particularly useful in calculating LV dimensions in order to determine LV function and myocardial viability  - gradual accumulation of a gadolinium based contrast agent followed by its delayed wash-out). Cost-effective analyses for this matter have yet to be performed.95HCM is an inherited autosomal-dominant myocardial disease caused by mutations in various genes encoding proteins of the cardiac sarcomere, which is characterized by significant LVH unexplained by either chronic pressure overload or infiltrative diseases.96Due to an enhanced rate of recognition by means of echocardiography, as well as its autosomal dominant transmission, the prevalence of HCM in the general population is higher than it was previously estimated, with one in every 200 adults (0.5 percent).97 It has been shown that symptoms may be exacerbated by the decrease in cardiac preload due to splanchnic vasodilatation postprandially.98Symptoms can vary widely from individual to individual, comprising fatigue, dyspnea on exertion, anginal or atypical chest pain, palpitations and even syncope.99 The prevalence of AF in the setting of HCM increases with age.100Patients with HCM who associate diastolic dysfunction are at an increased risk for supraventricular and ventricular arrhythmias, notably AF and even sudden cardiac death (SCD), especially in athletes.97Patients with HCM may associate LVOTO caused by the hypertrophied IVS.101 Moreover, the SAM of the MV contributes to the development of MR and to the severity of the LVOTO, which represents a frequent cause of disabling symptoms in HCM.102Notably, the presence of LVOTO worsens the prognosis by deteriorating left ventricular performance and by favoring the progression to more severe symptoms as well as raising chances of heart failure and death.97In the setting of LVOTO, physical examination of the patient may typically reveal a suggestive systolic murmur. On auscultation, LVOTO can be emphasized by a harsh crescendo-decrescendo systolic murmur at the apex that may radiate to the axilla and base.54When these findings do not occur at rest, provocative maneuvers such as Valsalva maneuver or amyl nitrite inhalation reduce preload and may be used to augment the intensity of the murmur.103Conversely, inspiration or hand grip increase afterload and therefore diminish the intensity of the murmur. For this reason, dynamic auscultation is crucial for the diagnosis of HCM.1Physical signs of MR associated to HCM may include cardiomegaly and a laterally displaced apical impulse. It is essential to seek for a loud holosystolic murmur best heard at the apex which may radiate into the axilla.Electrocardiography97 Signs of LVH associated with atrial enlargement  due to persistent MR are highly suggestive for HCM. LVH results in increased precordial voltages and repolarization changes . In the apical form of HCM, “giant negative T waves” in precordial leads may be observed in leads V2-V4. The axis may be deviated leftward.1A routine electrocardiogram (ECG) is a sensitive yet not specific method to diagnose HCM.Deep, narrow Q waves in lateral  and inferior  leads indicate asymmetrical septal hypertrophy.1 Features of Wolff Parkinson White syndrome  are frequently associated with HCM.104Furthermore, dysrhythmias such as supraventricular tachycardia may occur and even trigger malignant arrhythmias, eventually leading to SCD. AF is commonly seen in patients with advanced MR.Further investigations using noninvasive cardiac imaging are required in order to establish the diagnosis of HCM and evaluate the severity of the pathological changes.100,105Performing an echocardiography on all patients suspected of HCM has the purpose of identifying the presence of cardiac morphology abnormalities such as LVH as well as appreciating the extent of systolic and diastolic dysfunction and diagnose the presence of MR.106Comprehensive TTE is the initial imaging technique which demonstrates the pathological hallmarks of HCM: LVH, LVOTO and SAM of the MV.Tranthoracic echocardiography972D echocardiography provides useful data concerning the distribution and extent of LVH, especially during diastole in parasternal short-axis plane. Alternative imaging windows are also used to confirm measurements.105The criterion of a wall thickness exceeding 13 mm is used to diagnose HCM.107,108 and usually the LV ejection fraction is preserved. Evidence suggests that wall hypocontractility may develop before hypertrophy becomes evident.109The most commonly identified phenotypic variant of HCM is asymmetric hypertrophy, preferably localized within the basal segment of the anterior septum. This type is associated with LVOTO in 20-30% of cases110SAM of the MV consists in the anteriorly deviated movement of the mitral leaflets towards the ventricular septum during systole.111 The resultant pressure gradient leads to SAM.In patients with HCM, flow through the narrowed LVOT is characterized by elevated velocities and reduced pressure of blood ejection (Venturi effect).1,102 As evidence shows, SAM has been observed independently from HCM112 and precedes the increase of LVOT flow gradients.113In addition, structural abnormalities appear to be responsible for SAM of the MV.114SAM may occur in a wide range of patterns, depending on whether one or both mitral leaflets are involved and the place of chordal attachment .102,115SAM of the MV may result in dynamic LVOTO due to the impingement of the MV leaflets upon the hypertrophied IVS. The severity of obstruction in the LVOT is highly influenced by SAM, as the longer the mitral leaflets are dragged anteriorly, the narrower the LVOT becomes and the flow velocity increases further.3. Increased velocities from the LVOT to the aortic valve plane due to SAM are marked by the turbulent appearance of the color Doppler flow115 .LV outflow gradients are measured using continuous-wave Doppler imaging primarily in the apical long-axis view97,106Provocation tests using amyl nitrite, exercise or the Valsalva maneuver may be applied either for an enhanced diagnosis or for evaluating the response to pharmacologic agents.106,110As leaflets are pulled into the LVOT during SAM of the MV, leaflet apposition becomes asymmetric and incomplete, resulting in a MR jet which is directed posteriorly.116 In terms of timing, LVOTO typically has a late systolic peak and a “dagger shaped” continuous-wave profile.When the LVOT jet is present concomitantly with a MR jet, distinguishing signals from the two is challenging and the efficacy of a single flow assessment may be altered106Conversely, MR ejection period lasts longer and usually reaches outstanding peak velocities of more than 6 m/s during mid-systole.117The MR jet flow is easier to differentiate from LVOT jet flow when the Doppler beam is progressively oriented from the LVOT flow towards the MR flow. Furthermore, the two flows can be displayed separately when sweeping constantly from one flow to another.118 For instance, when the posterior leaflet is not mobile or long enough to follow the anterior leaflet, malcoaptation occurs and an interleaflet gap results.102 Chordal and papillary muscle displacement also interferes with leaflet coaptation, as they impose the limits of mobility allowed.119Evidence shows that leaflet length and mobility are important determinants of the severity of MR.2D imaging gives information upon leaflet morphology and coaptation efficiency.106Continuous-wave Doppler evaluates velocities from the LV apex to the MV plane in an attempt to determine the peak flow of MR.100 Papillary muscle insertion abnormalities are easier to identify when using off-axis views with 2D echocardiography.106A comprehensive examination is done in both parasternal and apical views from the medial to the lateral margins of the MV.Transesopahgeal echocardiographyTEE studies are mostly used for thorough periprocedural evaluation for planning purposes, although they are also useful when transthoracic views are not accurate enough.102,120, TEE may also identify any additional concurrent organic cause of obstruction such as a subaortic membrane associated with dynamic obstruction.105While TTE shows elongated leaflets in patients coming to surgeryThree-dimensional echocardiography121 and thickening as a consequence of repetitive septal contact and hypertrophied, anteriorly displaced papillary muscles.1,117By means of real-time 3D echocardiography the following morphological changes were identified to be responsible for SAM: leaflet elongation122,123, degree of diastolic function  and possibly even the risk of SCD124) and it may also be used to distinguish between phenotypic variations of HCM .123 CMR may also be used for monitoring post-surgical and post-pharmacologic treatment responses.123-125.As mentioned above, diagnosis of HCM traditionally relies upon clinical assessment and TTE in order to identify LVH, SAM and LVOTO. Heterogeneous phenotypic expression of the disease and technical limitations of echocardiography further complicate the diagnosis. CMR is an effective non-invasive imaging technique that can accurately measure LV mass126.Particular cases of patients with non-diagnostic clinical and TTE investigations, but with positive HCM on CMR  have been reported107,124Insofar as technique is concerned, CMR benefits from the feature of various enhancement patterns in afflicted myocardium, namely LGE. The technique is based on gradual accumulation of a gadolinium based contrast agent followed by its delayed wash-out. LGE appears in a number of diseases that involve the myocardium, myocarditis, various cardiomyopathies and myocardial infarction being the most common ones.126,127Non-invasive injection of the contrast agent helps describe tissue characteristics and may identify interstitial and replacement fibrosis typical for HCM. .LV crypts. Asymptomatic HCM patients were found to have crypts of up to 12 mm in the postero-basal ventricular septum which was undergoing hypertrophy. The significance of LV crypts remains to be determined.64,65Perhaps the most recent and important of CMR’s uses is the early detection of negative phenotypes, so called pre-clinical HCM. CMR studies by Maron et. al and Germans et al. have shown structural changes in the LV wall, in the form of 128Asymptomatic patients with minimal disease need an initial risk stratification by means of echocardiographic evaluation. If clinically significant MR is absent and thin leaflets are observed, the patient is encouraged to pursue a normal lifestyle, with clinical examinations and echocardiographic evaluation at every 3-5 years.In symptomatic MR and/or left ventricular dysfunction associated to MVP, afterload-reducing agents  are used for maintaining cardiac output. Caffeine, alcohol and cigarettes should be avoided.128,129In AF, maintenance of a normal ventricular response is ensured by administering beta-blockers and calcium channel blockers. Anticoagulants, such as anti-vitamin K drugs, are also recommended especially in patients with risk factors but also for the ones post MV replacement surgery.83The use of prophylactic antibiotics prior to periodontal and surgical procedures, although highly recommended in the past, has been limited to selected cases in recent years, according to the American Heart Association (AHA) guidelines.129Inotropic agents should be used in chronic severely symptomatic MR.ESC/EACTS guidelines suggest diminishing filling pressures in acute MR (with or without hypotension) with nitrates and diuretics, as well as afterload and regurgitant fraction reduction by means of nitroprusside therapy or an intra-aortic balloon pump.82In the case of hemodynamic shock, inotropic agents and an intra-aortic balloon pump should be used.72. The purpose of surgical correction in MVP is to restore MV competence.Although pharmacological therapy might relieve symptoms in severe MR or LV dysfunction (ejection fraction <60% or end-systolic diameter >45 mm), it cannot alter the natural development of the disease, surgery remaining the ultimate treatmentMitral valve replacement130An option for surgical correction is MV replacement. It can be performed using either a mechanical, or a biologic prosthesis. Although this method is considered to have the highest long-term efficacy, it has several drawbacks. Mechanical valves pose a risk of thromboembolism, thus needing lifelong anticoagulation therapy, while bioprosthetic valves rapidly deteriorate. Additionally, there is a high susceptibility of prosthetic-valve endocarditis or chordal cleavage during surgery.Mitral valve plasty83,131 MVP is usually repaired, either by resecting the flail and prolapsing leaflet scallop or by reconstructive techniques with artificial polytetrafluoroethylene (PTFE) chords. Annular dilation is often associated with MR and is corrected with a complete or partial annuloplasty ring. Posterior leaflet prolapse is more common, leading to severe MR. However, it has a higher success rate of durable repair compared with anterior leaflet prolapse or severe bileaflet prolapse. Ultimately, the most important indicator of long-term life expectancy in mitral repair remains the expertise of the surgeon.Surgical repairs are the preferred treatment for MVP. Although being associated with a higher post-operative recurrence of MR , mitral plasties have a lower peri-operative mortality.72Despite median sternotomy being the standard surgical approach, minimally invasive techniques are increasingly used nowadays , while the robotic approach is also gaining popularity. Both methods include partial sternotomies and restricted or mini-right thoracotomies.Transcatheter mitral valve repair72,129A cutting-edge method in MVP treatment is the transcatheter MV repair. The technique that mimics the surgical procedure proposed by Alfieri et al. offers an alternative to surgery for patients with symptomatic severe MR and high surgical risk. MitraClip therapy consists in edge-to-edge leaflet repair by clipping together the free edges of leaflets at their mid-portion. The Endovascular Valve Edge-to-Edge Repair Study (EVEREST II) compared MitraClip to surgery, showing that percutaneous repair of the mitral valve was less effective in reducing MR. However, this type of transcatheter repair was associated with similar improvement in clinical outcomes and with superior safety.Papillary muscle shortening132 Papillary muscle repositioning was also proposed as a reliable and safe technique in the repair of anterior leaflet prolapse, with excellent clinical and echocardiographic long-term results.133Papillary muscle shortening is another technique for MVP treatment used in the cases of abnormal muscle anatomy. There are two approaches for this technique: one by cutting a muscle section. An alternative method involves placing and tying a suture through the top of each muscle end and then passing it through the base, shortening them.Replacement of chordae tendineae134 Options to manage elongated chordae in MVP include natural chordal transfers (rarely used nowadays) or PTFE neochord replacements.132 Potential advantages of the “non-resection” approach include: preserved leaflet mobility, larger coaptation surface, implantation of larger prosthetic annuloplasty ring, which provides lower gradients due to larger orifice area, and lack of changes in annular geometry.134While mitral scallop “resection” methods have provided excellent long-term results, there is increasing evidence that supports “non-resection” techniques, with a “respect rather than resect” philosophy.135 During the last 6 years, two transcatheter techniques of placing artificial chordae have been developed72 The correct length of the chordae is determined by real-time echocardiographic guidance while observing the improvement in MR .132,135However, some improvements have been brought to the PTFE chordal replacement technique, as the classic procedure involves open-heart surgery.105In asymptomatic patients, the main concern is instructing them regarding the management of their disease. Intense physical activities should be avoided, changing their lifestyle should also be encouraged. Treatment of risk factors is also of paramount importance. Pharmacological therapy is usually the first line of treatment in order to prevent complications and disease progression. On an empirical basis, beta blockers and calcium channel blockers are the elected medications. Invasive treatment techniques are not recommended for these patients.136In symptomatic patients, the main concerns are treating symptoms, improving functional capacity and postponing the invasive treatment techniques. Symptoms such as angina or dyspnea should be treated using beta-blockers. For patients who present side effects or contraindications to beta-blocking drugs, verapamil or diltiazem therapy is recommended. AF should be managed using anticoagulation with vitamin K antagonists or direct thrombin inhibitors and anti-arrhythmic such as amiodarone, disopyramide or sotalol.137-142Patients with progressive disease  and who are refractory to medical therapy are suitable candidates for the following: septal myectomy with or without MV repair, alcohol septal ablation, chordae resection, papillary muscles surgery or even heart transplant.Septal myectomy140 and improve the MR grade. A study showed that after septal myectomy, all of the patients experienced a significant reduction in MR degree: no MR in 80%, mild in 19%, moderate in 1%.142 The main complications were atrioventricular nodal block, ventricular septal defect and aortic regurgitation.137It is a surgical procedure aimed at reducing the muscle thickening by removing a small amount of the thickened septal wall to decrease LVOTO143, including a decrease in the LVOT gradient from 78 mmHg to 11 mmHg and an improvement in 98% of the patients concerning the NYHA class .144,145This method is now associated with a less than 1% mortality riskSeptal myectomy and mitral valve repair138Whereas the surgical septal myectomy is the gold standard procedure in treating HCM patients, it does not directly address the involvement of the MV in the pathophysiology of HCM. A two-step procedure seems more efficient: septal myectomy, followed by MV repair with reconstruction.138 Other studies also support the dual method, as the data suggests a more satisfactory outcome compared to myectomy alone.146 Another study has also shown a significant clinical improvement in patients that underwent septal myectomy combined with MV repair, rather than in patients that underwent septal myectomy alone.147Excellent improvements have been observed, regarding the haemodynamics of the MV and clinical symptoms: NYHA class III and IV patients reached NYHA class I; the control echocardiography showed no MR, with a mean resting gradient of 15 mmHg (from a prior 73.5 mmHg).Septal myectomy and chordae resection140Another surgical option could be septal myectomy combined with the resection of the MV anterior leaflet chordae. A long-term study analysed the efficiency of this technique . The results showed improvements regarding the NYHA class: from class III-IV to asymptomatic and class I-II post-surgery. Also the LVOT gradient changed from 82 to 9 mmHg and the MR changed from grade 3 and 4 to lower grades.Papillary muscles surgery102 The surgical reorientation is performed to prevent ischemia, by suturing the fibrous portion of the papillary muscle in order to realign them as necessary and to reduce the hypermobility. The mean perioperative (114 mmHg) and predischarge (16 mmHg) LVOT gradients, show the effectiveness of this method. Moreover, the results have been compared to those of the patients who underwent isolated myectomy and myectomy plus MV repair/replacement, outlining the similarities regarding the outcome and concluding the surgical alternative for those who do not meet the septal thickness criterion for myectomy.148Papillary muscle surgery is the surgical approach that should be considered regarding displacement of the base of the anterolateral papillary muscle or its abnormal muscular insertions into or near the A1 scallop. Studies have shown the possibility of a longitudinal excision to thin the abnormal papillary muscle which caused the obstruction.Alcohol septal ablation149 It is considered an alternative to septal myectomy when the latter is unsuitable. The reported survival rate at 5 years is 91.7%. However, the procedure should not be encouraged in patients with marked septal hypertrophy (>30 mm), who do not meet the age requirements (>21 years of age) and have concomitant heart diseases that need surgical correction . Another important aspect is the risk of developing post-procedural AF or atrioventricular block.139Alcohol septal ablation (ASA) is a percutaneous, minimally invasive procedure which induces localized myocardial infarction, resulting in the thinning of the IVS, therefore leading to the reduction in dynamic outflow obstruction. For this method to be applied, LVOT should have a gradient more than 50 mmHg.Pacing and Implantable cardioverter defibrillators (ICDs)105 Despite the low mortality rate, complications are common, therefore the benefits and risks of this therapy should be carefully weighted.150-153Permanent pacing and ICDs are suitable for patients who cannot undergo surgical treatment and are at risk of developing life-threatening arrhythmias.Heart transplant154 Nonetheless, their survival rates after this procedure are comparable to those of patients transplanted for other cardiovascular diseases: the survival rates at 1, 5 and 10 years were 85%, 75% and respectively 61%.141HCM patients represent a small subset (<1%) of the whole patients undergoing heart transplant.Mitral Valve ProlapseThe outcome of patients with MVP mainly depends on the chosen treatment.Surgical treatment comprises of either repairing or replacing the MV.155,156 while others show comparable results. Bio-prostheses are more prone to reoperation. Therefore, the type of prosthesis cannot accurately predict the outcome of MVP patients who underwent valvular surgical replacement.157In terms of replacement surgery, bio- and mechanical prostheses have similar mortality and follow-up rates. Bleeding risk evaluation offers varying results with some studies showing a more significant risk of bleeding for mechanical valves158MV repair carries a vastly lower mortality compared to replacement surgery both immediately following surgery and on long-term follow-up . This tendency is also valid for myxomatous valvulopathies that required surgical treatment, making valvular repair the elective treatment for patients with MVP.Hypertrophic cardiomyopathy159-162 Over 65 years of age, however, ASA had a more significant decrease in gradient and symptoms than septal myectomy. Regarding mortality, certain studies have shown similar peri-procedural rates162,163, while others have shown a higher incidence of complications in the case of ASA.164,165 There is an ongoing debate which procedure should be favored, this being highly dependent on patient types and operative expertise.166Patients under 65 years of age who underwent septal myectomy had better survival rates and lower severity of symptoms than patients who underwent ASA. ASA patients became completely asymptomatic in only about half of the cases.155A study compared LVOT gradient, MR and SAM in patients who underwent septal myectomy and concomitant MV repair or MV replacement. Preoperative peak LVOT gradient was 63.7 mmHg with severe MR present in 88% of the cases and with SAM in 94%. Following surgery LVOT gradient decreased to 10 mmHg, 21% of patients, still presented chordal SAM and MR was absent or mild in 75% of cases and moderate in 21%. At late follow-up, LVOT decreased to 2.5 mmHg, SAM was no longer present in any of the patients and only 2 had MR and 84% of patients were in NYHA class I or II.72Surgery is prone to remain the gold standard therapy in low-risk or intermediate-risk patients with MVP.72,135 Supporting this concept, robotic surgery has come to the aid of MVP treatment. This technique allows increased operative dexterity and ambidexterity, higher degree of movement freedom (compared with the endoscopic approach), tremor-free movements, by-pass of the fulcrum effect (often manifested during endoscopic procedures) and use of 3D high definition imaging. Furthermore, patients directly benefit from the smaller incisions, shorter length of hospitalisation, sooner return to the pre-operative level of functional activity and decreased blood transfusion requirements. Some limitations in robotic MV surgery remain the increased operative times and lack of haptic feedback. Morbidity and mortality rates are similar to both classic cardiac surgery and minimally invasive procedures.167The new trend nowadays is developing minimally invasive techniques.168Additionally, a novel patient-specific virtual valvular repair strategy was implemented, in order to decide pre-operative selection of the optimal repair techniques. Personalized computational modeling for MV repair, along with 3D echocardiographic guidance can provide higher outcome predictability and, ultimately, more effective medical care for the patient.169In the pursuit of overcoming some of the MV replacement limitations, tissue engineering-based techniques have been approached. Among various scaffolds used in tissue engineering, the decellularized heart valve (DHV) has attracted much attention, as a result of its native structure and comparable haemodynamic characteristics. The clinical application of DHV remains under debate .170 and the attainment of a controlled expression of exogenous genes.171 Systemic administration of cardiac adeno-associated virus (AAV) and a cardiomyocyte-specific promoter specifically targets the heart.The applicability of gene therapy is limited to dominant monogenic muscle disorders such as HCM, mitigating the consequences of myofilament mutations. Limitations comprise the receptivity of muscle to gene transduction, gene delivery using vectors such as adeno-associated virus 9 (AAV9)172In severe cases of inherited cardiomyopathy associating systolic heart failure with a heart transplant as an ultimate treatment option, gene therapy plays an important role. Commonly, homozygous and double heterozygous mutations in the sarcomeric genes predispose to rapidly progressive cardiomyopathies.-splicing, exon skipping and RNA silencing.173Gene therapy may either remove mRNA mutations or introduce functional proteins in the place of mutant endogenous ones. Techniques directly targeting endogenous mutant sarcomeric mRNA or RNA are spliceosome-mediated RNA trans-splicing (SMaRT) is an approach which creates a full-length repaired mRNA by splicing together a mutant pre-mRNA and a therapeutic pre-trans-splicing molecule, both transcripted independently (delivered by AAV).174Spliceosome-mediated RNA trans175 Despite the small internal deletion, the protein’s functionality is unaltered. AAV9 administration in myosin-binding protein C 3 – knock in mice (MYBPC3-KI mice) produced a stable functional protein which temporarily prevented the disease phenotype.176 However, reaching the appropriate level of intracellular oligonucleotide that entirely suppresses missense mutations remains a major challenge.171Different strategies use antisense oligonucleotides (AONs) to mediate the skipping of mutated exons. Their role is to restrict the binding of regulatory splicing proteins that mediate exons inclusion into the mature mRNA by concealing exonic splicing enhancer motifs.177Severe sarcomeric cardiomyopathies due to bi-allelic MYBPC3 mutations have been associated with fewer mutant proteins. The causal therapy in this particular case consists of replacing endogenous mutant myosin binding protein-C (cMyBP-C) with exogenous functional cMyBP-C. In a recent study performed on homozygous MYBPC3-KI mice, one systemic injection of AAV9 encoding cMyBP-C under the control of human cardiac troponin T promoter in neonatal mice has enabled a 34 week long prevention of the disease phenotype, namely LV hypertrophy.2+ desensitizers owing to their intrinsic Ca2+-binding properties. Signaling of muscle contraction is impeded by compounds that bind to either the N-terminal regulatory domain or the C-terminal structural domain of cTnC. Consequently, the Ca2+-dependent interaction between cTnC and cardiac troponin I (cTnI) is prevented. Furthermore, cTnC is structurally homologous with calmodulin (CaM), making CaM-binding compounds potential modulators of Ca2+ sensitivity in the cardiac myofilament.173Cardiac troponin C (cTnC) is the target of genetic manipulation with the aim to reverse primary functional changes of the sarcomeres. Newly formed cTnC mutants are produced in order to behave as Ca178Vertically transmitted HCM may be prevented when a couple undergoes assisted reproduction by in vitro fertilization. First,one cell is removed from each embryo and analysed for specific mutations. Subsequently, mutation free embryos are selected and transferred into the uterus.179Conclusively, based on the fact that HCM does not significantly affect longevity, genetic engineering is not a priority nowadays. Gene therapy is mostly suitable for recessively inherited defects induced by mutations which partially or completely alter enzyme function.The mitral valve undergoes similar leaflet elongation and thickening changes, although through different mechanisms, in mitral valve prolapse and in hypertrophic cardiomyopathy. These mechanisms involve disruption of the homeostasis of the extracellular matrix in mitral valve prolapse, while in hypertrophic cardiomyopathy there are many theories, but a common mechanism is suspected. Both pathologies involving the mitral valve have genetic causes: in mitral valve prolapse, most, if not all changes, revolve around the activity of TGF-β, whereas the mutations responsible for the modifications in hypertrophic cardiomyopathy are in genes that mostly codify sarcomeric proteins.The role of cardiac imaging is vital for diagnosing both pathologies and the consequent mitral regurgitation. Three-dimensional echocardiography has an emerging role in mitral valve prolapse diagnosis and is comparable to cardiac magnetic resonance imaging in the context of this disease. Also, three-dimensional echocardiography is routinely recommended and has a high potential benefit. Cardiac magnetic resonance imaging emerges in the diagnosis of hypertrophic cardiomyopathy through an accurate measurement of characteristic features and it could possibly even evaluate the risk of sudden cardiac death.Surgery is the curative treatment for these diseases involving the mitral valve. Mitral valve repairs are suitable interventions for the couple of pathologies that induce mitral regurgitation. While mitral valve prolapse only requires mitral plasty, in hypertrophic cardiomyopathy septal myectomy and mitral valve repair are required. In addition, cutting edge techniques for treating mitral valve prolapse were developed, such as decellularized heart valve, robotic surgery and virtual valve repair simulation. Regarding future perspectives for hypertrophic cardiomyopathy, gene therapy is a promising field, directly targeting endogenous mutations in the sarcomere.High levels of TGF-β are involved in the pathogenicity of mitral valve prolapse◊ Sarcomeric protein mutations are mostly incriminated for the occurrence of hypertrophic cardiomyopathy◊ An accurate description and a better understanding of the process of leaflet elongation will be essential in establishing new therapies for the treatment of both diseases◊ Early diagnosis, grading and treatment of mitral regurgitation before symptomatology onset or irreversible ventricular damage lead to an excellent chance of improved quality adjusted life years◊ 3D transesophageal echocardiography is comparable to cardiac magnetic resonance regarding feasibility and accuracy of diagnosis in mitral valve prolapse◊ Three-dimensional echocardiographic assessment of patients with mitral valve prolapse is now recommended for routine examination◊ Multimodality imaging enhances the diagnosis accuracy in patients with hypertrophic cardiomyopathy and identifies the structural abnormalities in the mitral valve responsible for the presence of systolic anterior motion◊ In patients with hypertrophic cardiomyopathy and dynamic left ventricular outflow tract obstruction, transesophageal echocardiography may recognize additional concurrent organic causes of obstruction such as a subaortic membrane◊ Cardiac magnetic resonance imaging is an increasingly useful tool in diagnosing infra-clinical cases of hypertrophic cardiomyopathy◊ Personalized computational modeling for mitral valve repair along with three-dimensional ecocardiographic guidance can provide a pre-operative selection of the optimal repair technique◊ For severe cases of hypertrophic cardiomyopathy, a promising therapeutic alternative is gene therapy, using different strategies to remove mRNA mutations or to replace mutated endogenous proteins with functional ones, in this manner delaying phenotypic expression◊


Wooden breast is one of several myopathies of fast-growing commercial broilers that has emerged as a consequence of intensive selection practices in the poultry breeding industry. Despite the substantial economic burden presented to broiler producers worldwide by wooden breast and related muscle disorders such as white striping, the genetic and etiological underpinnings of these diseases are still poorly understood. Here we propose a new hypothesis on the primary causes of wooden breast that implicates dysregulation of lipid and glucose metabolism. Our hypothesis addresses recent findings that have suggested etiologic similarities between wooden breast and type 2 diabetes despite their phenotypic disparities. Unlike in mammals, dysregulation of lipid and glucose metabolism is not accompanied by an increase in plasma glucose levels but generates a unique skeletal muscle phenotype, i.e., wooden breast, in chickens. We hypothesize that these phenotypic disparities result from a major difference in skeletal muscle glucose transport between birds and mammals, and that the wooden breast phenotype most closely resembles complications of diabetes in smooth and cardiac muscle of mammals. Additional basic research on wooden breast and related muscle disorders in commercial broiler chickens is necessary and can be informative for poultry breeding and production as well as for human health and disease. To inform future studies, this paper reviews the current biological knowledge of wooden breast, outlines the major steps in its proposed pathogenesis, and examines how selection for production traits may have contributed to its prevalence. The last half century has witnessed remarkable gains in commercial broiler production characterized primarily by rapid growth, high feed efficiency, and high breast muscle yield , b. Alonfatty acid translocase (CD36), fatty acid binding protein 4 (FABP4), lipoprotein lipase (LPL), and peroxisome proliferator-activated receptor gamma (PPARG) among others  – providing non-esterified fatty acids and monoglycerides for use by surrounding tissues  (PFKFB1 (unpublished data), in 7-week-old affected birds. In that study, PFKFB3 and PFKFB1 were the only detected HIF1-dependent gene that were downregulated rather than upregulated   as well egulated . The supegulated . Hypoxiaegulated . What muReduced glucose uptake from plasma is an unlikely cause of reduced glycolysis as there is no difference in plasma glucose levels between affected and unaffected birds , b and ePFKFB3 in affected broilers  signaling , increasbroilers . PFKFB3 s of ROS .In mammals, lipotoxic inhibition of glucose oxidation in skeletal muscle and adipose tissue is accompanied by downregulation of insulin-sensitive glucose transporter 4 (GLUT4), resulting in the insulin resistance and high plasma glucose levels that characterize type 2 diabetes . ReducedThe polarity and size of glucose molecules prevent their transport across lipid membranes by simple diffusion . Two famAvian glucose transport and insulin signaling are not as well characterized as those of mammals , but it The reliance on insulin-independent glucose transporters in chicken skeletal muscle may explain why there are no mammalian skeletal muscle disorders that are equivalent to wooden breast. Rather, the wooden breast phenotype shares striking similarities with various complications of type 2 diabetes in smooth muscle and cardiac muscle, such as atherosclerosis, diabetic cardiomyopathy and myocardial fibrosis, diabetic nephropathy, pulmonary fibrosis, diabetic retinopathy, and non-alcoholic fatty liver disease. These diseases frequently involve lipid accumulation, inflammation, oxidative stress, calcium dysregulation, endoplasmic reticulum stress, hypoxia, hypertrophy, and fibrosis – features that have also been well-documented in wooden breast. The greater role of insulin-independent glucose transport in cardiac and smooth muscle allows glucose uptake even when glycolysis and glycogenesis are impaired. The importance of insulin-insensitive glucose transport in development of diabetic retinopathy , atherosThe suppression of glycolysis and glycogenesis concurrent with unchanged or increased uptake of glucose from blood results in increased flux of glucose through alternative metabolic pathways , includiGlucose that is phosphorylated to glucose-6-phosphate can directly enter both the pentose phosphate pathway and the glucuronic acid pathway. In addition to generating carbon skeletons and ribose 5-phosphate, a precursor to nucleotide synthesis, the pentose phosphate pathway is a major source of NADPH, the main reductant that drives free radical detoxification and anabolic growth . AccumulGFPT2, phosphoglucomutase 3 (PGM3), and UDP-N-acteylglucosamine pyrophosphorylase 1 (UAP1) – show increased expression in the pectoralis major of high-feed-efficiency broilers, which are more susceptible to wooden breast than those with low feed efficiency , a nucleotide sugar and coenzyme used for protein glycosylation and the synthesis of glycosaminoglycans, proteoglycans, and glycolipids . The genficiency . In agreficiency . Increasficiency . Proteogtransforming growth factor β 3 (TGFB3) in the pectoralis major muscle of affected birds at 7 weeks  and greater accumulation of sorbitol  membranes that use ATP to translocate Ca2+ from the cytoplasm to the SR lumen  formation of the mitochondrial permeability transition pore and mitochondrial depolarization cause release of Ca2+ from the mitochondria, and (3) depolarization of the plasma membrane causes an influx of Ca2+ from extracellular spaces. The SR lumen serves as the most important Ca2+ store in the cell (2+ from the SR lumen by activating ryanodine and inositol trisphosphate (IP3)-sensitive calcium channels   . ExpressRNA ISH) . TranscrRNA ISH) . Lipid sRNA ISH) .Venous and perivascular inflammation and lipid accumulation are the first microscopic signs of wooden breast, potentially contributing to the edema, petechial hemorrhages, and tissue damage that are macroscopically apparent in late stages of the disease . It has toll-like receptor 2 type 2 precursor (TLR2-2) was one of the top 30 genes identified as a biomarker of wooden breast severity, with significant elevation in moderately affected birds compared to unaffected or severely affected birds (The participation of LPL in the pathogenesis of atherosclerosis is two-fold: it mediates both the increased hydrolysis of lipoprotein triglycerides as well as the retention of lipoprotein remnants. High LPL activity increases local hydrolysis of triglycerides in portomicrons and VLDL, which produces free fatty acids, portomicron remnants, intermediate-density lipoproteins, and low-density lipoproteins . Elevateed birds . The auted birds . Due to Endothelial cell damage and apoptosis due to increased lipoprotein metabolism increases the permeability of the endothelium and triggers leukocyte adhesion and transmigration into the vessel wall . LipoproConsolidation of poultry breeding and intense selection for production traits have undoubtedly played an oversized role in the rise of muscle disorders such as wooden breast, white striping, and spaghetti meat among commercial broilers. Even without completely understanding the genetic architectures underlying these traits, it is possible to speculate how selection for specific performance metrics might increase the predisposition of meat-type chickens to these myopathies. Much of this speculation can be framed in the context of supply and demand of nutrients in the pectoralis major muscle. Juvenile growth rate, which has increased substantially since the 1950s independent of improvements to feed formulation  and whicSelection for feed efficiency has also raised digestive and absorptive capacity but may not increase the overall supply of nutrients to the body as increased energy absorption from feed is at least partly offset by reduced feed consumption. A larger effect of using feed efficiency as a major selection criterion relates to its correlation with fat distribution and blood lipid levels . Unlike It should be noted, though, that wooden breast does not correlate perfectly with performance traits like growth rate, feed efficiency, abdominal fat percentage, or breast muscle yield, suggesting the existence of etiological factors that may be unrelated to nutrient partitioning. For example, a mutation that affects coupling of lipid or glucose uptake and utilization in the pectoralis major might constitute the spark on the proverbial fire of nutrient accumulation and toxicity. We believe that the wooden breast phenotype in commercial broilers is a manifestation of lipotoxicity and glucotoxicity resulting from the chronic oversupply of both lipids and carbohydrates to the pectoralis major and also the disruption of normal lipid and glucose metabolism. Dependence on insulin-independent glucose transport in the skeletal muscle of chickens causes lipid accumulation in the pectoralis major to be accompanied by unchanged or increased uptake of glucose, causing metabolic and structural alterations that closely resemble complications of diabetes in smooth and cardiac muscle of mammals. In addition to improving our understanding of the etiology and pathogenesis of wooden breast and related myopathies, this hypothesis supports the use of these muscle disorders as models of human metabolic diseases.The datasets generated for this study are available on request to the corresponding author.JL wrote the original draft of the manuscript. BA provided indispensable guidance, expertise, and unpublished data from previous research. All authors contributed to critical feedback and helped to shape the research, analysis, and manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


APC gene is a common early event in colorectal cancer, however lower rates have been reported in younger cohorts of colorectal cancer patients. In sporadic cancer, mutations are typically clustered around a mutation cluster region, a narrowly defined hotspot within the APC gene. In this study we used a sequencing strategy aimed at identifying mutations more widely throughout the APC gene in patients aged 50 years or under. We found high rates of APC mutation in our young cohort that were similar to rates seen in older patients but the mutations we found were spread throughout the gene in a pattern more similar to that seen in inherited rather than sporadic mutations. Our study has implications both for the sequencing of the APC gene in early-onset colorectal cancer and for the etiology of this disease.Mutation of the APC gene is a common early event in CRC but is reported at lower rates in early-onset colorectal cancer (EOCRC) than in older patients. Here we investigate the APC mutation status of a cohort of EOCRC patients in New Zealand using a novel sequencing approach targeting regions of the gene encompassing the vast majority of known APC mutations. Using this strategy we find a higher rate (72%) of APC mutation than previously reported in EOCRC with mutations being spread throughout the gene rather than clustered in hotspots as seen with sporadic mutations in older patients. The rate of mutations falling within hotspots was similar to those previously seen in EOCRC and as such our study has implications for sequencing strategies for EOCRC patients. Overall there were low rates of both loss of heterozygosity and microsatellite instability whereas a relatively high rate (40%) of APC promoter methylation was found, possibly reflecting increasing exposure of young people to pro-oncogenic lifestyle factors.While overall colorectal cancer (CRC) cases have been declining worldwide there has been an increase in the incidence of the disease among patients under 50 years of age. Mutation of the  Over recent decades there has been an overall drop in the worldwide incidence rates of colorectal cancer (CRC) worldwide, primarily due to increased rates of colonoscopy screening which leads to the early detection and removal of precancerous polyps ,2. HowevAPC) gene is the most frequent early genetic event in the progression of colorectal carcinogenesis. APC mutations are found in the earliest microscopic adenomas [Mutation of the tumour-suppressor adenomatous polyposis coli  between codons 1286 and 1513 [APC mutation have focused their efforts [APC mutations that fall outside this region are not detected.Despite mutations of the patients ,21, addipatients ,22,23 thpatients , a subsetability . Howeverand 1513 . Consequ efforts ,28,29,30APC mutation in this cohort was similar to that reported elsewhere [APC gene, enabling identification of both the presence and location of mutations throughout the APC gene as a whole. Further investigation was undertaken to determine whether loss of heterozygosity [APC gene promoter region [APC gene allele in these early-onset colorectal cancers. The occurrence, type, and location of APC mutations are reported, as is evidence of microsatellite instability, loss of heterozygosity, and APC promoter methylation, and these findings are compared to clinical features of the tumours.The aim of this study was to explore the molecular genotype of a cohort of tumour tissues collected from EOCRC patients in Canterbury, New Zealand. The first objective was to identify whether the rate of lsewhere ,21. For zygosity  and/or mr region  may haveThe cohort of 25 early-onset CRC cases consisted of 14 (56%) women and 11 (44%) men aged 50 years or under at diagnosis  . The tumAPC mutation while six tumours had two mutations. The mutations consisted of 14 nonsense, six frameshift, three missense, and one splice region mutation  and relative (>20%) read number were found in 18/25 (72%) tumour samples and confirmed by Sanger sequencing. Twelve tumours had a single mutation . Sequencc.3374T>C variant) results in a substitution at codon 1125 of a valine to an alanine (p.V1125A) and is regarded as a conservative change as they are closely related amino acids. Coupled with the occurrence of the variant in the general population [c.3374T>C variant is considered benign.One of the germline mutations , was accompanied by loss of the wild type allele in the tumour tissue  of patients had mutations located within the mutation cluster region [The mutations found in the early-onset cohort were distributed widely across the first 1600 codons of r region , a totalOf the 24 samples that were stained for mismatch repair proteins, 21 stained for all four mismatch repair proteins and were therefore considered microsatellite stable. All three of the remaining samples displayed microsatellite instability, with one negative for MSH6 staining and two negative for PMS2 staining. The three mismatch repair deficient tumours did not cluster at any location in the colon, as they were found in the ascending colon, splenic flexure and the sigmoid colon, respectively. Neither was there any association of microsatellite instability with age or gender.BRAF mutation. This sample was the only adenosquamous carcinoma in the cohort. This combination of a BRAF mutation in a microsatellite stable adenosquamous colon cancer has been reported before [One of the 21 samples that stained positively for all four mismatch repair genes was reported to have a d before .APC locus was found in 3/25 (12%) samples in the cohort. Strikingly, the three samples with LOH all carried an APC mutation clustered around codon 1300, a phenomenon previously reported in sporadic CRC [Loss of heterozygosity at the adic CRC . As withAPC 1A promoter, responsible for the predominant APC isoform, was detected in 10/25 (40%) of tumours, a higher rate than previously reported in CRC [APC promoter methylation in CRC [APC promoter methylation with age (mean age 43.5 years vs 44 years for the whole cohort), gender  or tumour location .Methylation analysis of the CpG island at the d in CRC , althougn in CRC . There wAPC gene mutation in a cohort of EOCRC tumours, with sporadic mutations occurring throughout the gene rather than clustering in one region as expected. The APC gene is long, encompassing 8529 bases of coding sequence over multiple exons covering over 100 kilobases of chromosome 5, making targeted sequencing strategies cumbersome and expensive. Therefore, previous studies have focused on mutation hotspots in the gene, particularly the mutation cluster region between amino acids 1286 and 1513 [APC mutations [In this study we found a higher than anticipated rate of and 1513  or more utations . AlthougAPC with very low rates of mutation in sporadic CRCs were identified using the Catalogue of Somatic Mutation In Cancer (COSMIC) database, and excluded from our sequencing strategy. In this study, exons 5, 6, 8, 9, 11, 12 and 13, as well as exon 15 from amino acids 788 to 1593 were targeted. These exons encompass the vast majority of non-synonymous mutations of the APC gene in the COSMIC database, and each was sequenced. This approach identified 24 mutations in 18/25 (72%) tumour samples across these regions of the APC gene, a notably higher rate than some previous studies looking at APC mutation in early-onset CRCs [APC gene coverage by the methodology used here. Importantly, if we had only sequenced the mutation cluster region, this number would have dropped to eight out of 25 tumours (32%). Likewise, mutations in the final exon of the gene were identified in only 14/25 (56%) of the samples. These findings convincingly highlight that protocols applied to study APC mutations are of critical importance, and that studies limited to “hotspot” regions of the gene may significantly under-report the mutation rate.Regions of set CRCs ,21 that APC mutations. While the p.V1125A variant was deemed to be benign, the p.E1317Q variant has been associated with colorectal cancer previously [APC mutations in FAP [APC locus. Accordingly, the lack of family history might be due to the single mutant allele alone not being sufficient for carcinogenesis, suggesting a second genetic hit is required for the pathogenicity of the p.E1317Q mutation to occur, an example of the damaging potential caused by loss of heterozygosity. It was noted that this patient did not present with polyps and would therefore be unlikely to be considered as a possible case of FAP and therefore not tested for APC mutation. As such, although we cannot rule out the possibility that the mutation has arisen de novo in this patient, it is likely that this patient has an atypical FAP phenotype and our finding may have implications for FAP testing.Despite known familial colorectal cancer syndromes being excluded, two patients were found to have germline eviously . Notablys in FAP . While tWe found that 8/24 (33%) mutations occurred within the MCR as defined by Miyoshi and colleagues . RemovinAPC predominantly result in truncated proteins that retain some function essential for the survival of the cells [APC mutations affects the properties of the resultant protein and the tumour phenotype [APC mutations are scattered across the 5′ half of the gene, with notable hotspots at codons 1061 and 1309, somatic mutations tend to occur within the MCR [Mutations in he cells . The lochenotype . While f the MCR . This reAPC mutations occurring outside the MCR in EOCRC suggests that the β-catenin binding capacity of truncated APC is of less importance in EOCRC than in older patients, and that alternative functions of APC may be at play in these tumours.Kohler and colleagues showed that mutations in the MCR resulted in the disruption of the third 20-amino acid repeat region while maintaining the first 20aa repeat. They also showed by co-immunoprecipitation that the second 20 amino acid repeat region, unlike the other two, had no β-catenin binding capacity therefore all the mutations within the MCR produced truncated proteins with similar β-catenin binding efficiency . Our finThree decades ago biological differences were identified in tumours located in either the proximal (right-sided) or distal (left-sided) colon, leading to the proposal of distinct categories of colorectal cancer based on tumour location . In partAPC mutations in the MCR that result in 2–3 intact 20-amino acid repeats are more likely to be found in proximal tumours, while mutations leaving only 1 or no 20-amino acid repeats tend to be present in distal CRC [APC gene than somatic mutations, of which a large proportion are found in the MCR [APC mutations in EOCRC more closely resembled the pattern of APC mutations seen in FAP fits with the observation that EOCRC tumours are predominantly distal. In support of this hypothesis is the observation that the majority of EOCRC tumours do not show microsatellite instability and those that do are usually due to Lynch Syndrome [This leads to an intriguing hypothesis. stal CRC . Inherit the MCR . Our finSyndrome . In popuSyndrome . Our finAPC gene in 40% of EOCRC tumours, a higher rate than reported in overall CRC [APC gene promoter may play an important role in EOCRC, despite lower methylation more generally. A previous study of patients presenting with CRC or colorectal polyps found APC methylation present in 8/50 (16%) samples [APC promoter methylation may play a significant role in EOCRC.The CpG island methylator phenotype (CIMP), where multiple tumour suppressor genes are silenced by promoter methylation, is reportedly found less in EOCRC patients than in older-onset CRC patients, with one study reporting the CIMP to be absent in all 47 EOCRCs, but present in 15/49 31%) of CRCs in over 60 year olds . However% of CRCs samples . When thAPC gene does not inform a direct role for diet in the genesis of early onset CRC. Moreover, whether this effect is the result of early maternal nutrition that can markedly affect the epigenetic patterning in the fetus is also beyond the scope of this study. However, our finding of tumour-specific APC promoter methylation in 40% early-onset CRC, with or without retention of a homozygous APC gene, highlights growing awareness that environmental factors need to be taken into consideration as we try to find ways to reduce the number of young people developing this disease.While diet is a major environmental factor proposed to influence DNA methylation in the colon , a findiSamples from 25 patients with early-onset colorectal cancer, diagnosed at or under the age of 50 years, were obtained from the Cancer Society Tissue Bank, Christchurch, New Zealand. Patients with known hereditary syndromes, HNPCC or FAP were excluded. The samples consisted of frozen tumour tissue as well as matched normal tissue taken at the time of surgery. The study was granted ethics approval by the University of Otago Human Ethics Committee (H18/143).DNA was extracted from up to 25 mg of frozen tissue using a DNeasy Blood and Tissue kit . Prior to extraction the tissue was homogenized in a Precellys Evolution homogenizer  with 180 µL lysis buffer using 2.8 mm zirconium oxide beads in reinforced 2 mL microtubes. DNA was then extracted according to the manufacturer’s instructions.APC gene sequence of the tumour samples and matched normal tissue was determined by running pooled, indexed PCR products on an Illumina MiSeq instrument following the previously described protocol [APC were generated using a two-step PCR approach. In the first PCR step, regions of the APC gene, accounting for the vast majority of known cancer-associated mutations, were amplified. APC-specific primers were designed with an additional 18 bp of known non-specific sequence that was used as a priming site for the second PCR reaction . Sequencing libraries were run on a DNA7500 Bioanalyzer chip  to determine the average library size. Libraries were sequenced on an Illumina MiSeq using V2-500 cycle reagent kits .Raw paired end reads were cleaned with Trimmomatic v.0.35 . CleanedAPC sequences obtained above were used to detect loss of heterozygosity (LOH) by comparing levels of each allele at four single nucleotide polymorphisms (SNPs) within the APC gene. SNPs showing heterozygosity, by presence of both alleles, in normal tissue were considered to have LOH if the read count of one allele was reduced in relation to the alternate allele in tumour tissue. A low number of alleles present for the missing allele likely reflected non-tumour cells, such as lymphocytes, within the tumour tissue. The four SNPs analysed were rs2229992, rs351771, rs1801166 and rs41115. If all the informative SNPs within the APC gene in a single patient showed loss of an allele in the tumour tissue then the tumour was considered to display LOH at the APC locus.The Mutations detected using the method above were confirmed by Sanger sequencing. Briefly, purified PCR products were prepared for sequencing using BIG Dye chemistry  and sequenced on an ABI3700xl Genetic Analyser .Slides of sectioned tumour tissue were available from 24 of the 25 patients, and these were stained for mismatch repair proteins to assess microsatellite instability . BrieflyAPC promoter 1A sequences using previously published conditions and primers [DNA was modified by sodium bisulphite using EZ DNA Methylation-Gold kit  according to the manufacturer’s protocol. Methylation-specific PCR (MSP) was used to amplify methylated and unmethylated  primers .APC mutations at a rate similar to that found in later-onset CRC, suggesting that similar mechanisms underlie tumour development in both age groups and that the earlier onset seen in the current cohort may be due to environmental factors. However, we found that the distribution of APC mutations more closely resembled that of familial APC mutations than sporadic later-onset CRC, despite the mutations being almost exclusively sporadic. This has implications for APC sequencing techniques as methodologies focusing on the mutation cluster region rather than the whole gene may miss a substantial number of APC mutations in sporadic EOCRC.Our study of a cohort of colorectal tumours from patients diagnosed under the age of 50 years identified


Cholangiocarcinoma (CCA) is one of the most lethal cancers, and its rate of occurrence is increasing annually. The diagnoses of CCA patients remain elusive due to the lack of early symptoms and is misdiagnosed as HCC in a considerable percentage of patients. It is crucial to explore the underlying mechanisms of CCA carcinogenesis and development to find out specific biomarkers for early diagnosis of CCA and new promising therapeutic targets. In recent times, the reprogramming of tumor cells metabolism has been recognized as a hallmark of cancer. The modification from the oxidative phosphorylation metabolic pathway to the glycolysis pathway in CCA meets the demands of cancer cell proliferation and provides a favorable environment for tumor development. The alteration of metabolic programming in cancer cells is complex and may occur via mutations and epigenetic modifications within oncogenes, tumor suppressor genes, signaling pathways, and glycolytic enzymes. Herein we review the altered metabolism in cancer and the signaling pathways involved in this phenomena as they may affect CCA development. Understanding the regulatory pathways of glucose metabolism such as Akt/mTOR, HIF1α, and cMyc in CCA may further develop our knowledge of this devastating disease and may offer relevant information in the exploration of new diagnostic biomarkers and targeted therapeutic approaches for CCA. Cholangiocarcinoma (CCA) is a primary malignancy that originates from the cholangiocytes lining the biliary tree, also known as bile duct cancer. CCA is classified according to anatomical position, as either intrahepatic (iCCA), arising in the liver, and extrahepatic (eCCA), arising outside the liver. Extrahepatic cholangiocarcinoma can then be further classified as perihilar (pCCA) and distal cholangiocarcinoma (dCCA). The majority of CCA tumors are found in the perihilar and distal region, whereas only 10% are reported as intrahepatic, although responsible for 10–20% of all hepatic tumors . CCA chaThe incidence of CCA varies considerably between East-West dichotomy, reflecting variations in genetic and environmental risk factors. The highest incidence of CCA is reported in the north-east part of Thailand with rates of  in men and  in women; which is almost 100 fold more than Europe and North America , whereas Australia has the lowest number of CCA incidence with 0.4/100,000). The prevalence of CCA is increasing worldwide for unknown reasons  can stimulate increased glucose consumption and lactate production in the cells. This process is regulated by hypoxia-inducible factor 1 (HIF-1), is a transcription factor complex , 29. HIFAn interesting study of Xu et al. showed that decreased expression of SIRT3 was correlated with high rate of glycolysis in CCA. Consistently, changes in glucose metabolism were observed in SIRT3 knockout mice. Furthermore, the authors also confirmed that SIRT3 prevents the Warburg effect in CCA cells and a xenograft mouse model by inhibiting the HIF1α/PDK1/PDHA1 pathway. Collectively, this study suggests that SIRT3 shows anti-Warburg effect activity via regulating the HIF1α/PDK1/PDHA1 pathway and may be a potential therapeutic intervention to impair CCA progression .Many previous studies have shown that some glucose metabolism genes are directly regulated by cMyc . These gIn CCA cells, the SIRT2/cMYC pathway was reported to play a critical role in modulating glucose oxidative metabolism to serine anabolic metabolism. Furthermore, the high level of SIRT2/cMYC pathway not only converts glucose to serine, but also provides antioxidants for oxidative stress resistance in CCA cells. Therefore, the metabolic reprogramming induced by SIRT2/cMYC pathway may provide a new therapeutic target for CCA .Targeting cancer cell metabolism has become a significant emerging field to address effective cancer therapies, including tumor relapse and drug-resistance. To inhibit glucose metabolism in cancer cells, glycolytic enzymes  and glucose transporter (GLUT 1-4) have been considered as therapeutic targets . GLUT1, Alternative potential target is the adaptive characteristic of cancer cells inside the tumor microenvironment. A cancer cell can transmit its metabolism in heterogeneous environmental conditions, glucose deficiency, hypoxia, and acidic environment; this adaptation to metabolic response by cancer cells plays an essential role in cell metastasis or chemotherapy resistance . HIF1α iThe reprogramming of glucose metabolism in malignant cells is a multi-factor and multi-step route that can be controlled by carcinogenic signaling processes, and by epigenetic modulations. The advancement in cancer metabolism research significantly improved our knowledge of carcinogenesis and gave several potential targets for cancer. The drug that targets glycolytic enzymes or glycolysis pathways revealed several encouraging effects in cancer prevention and therapy . The cauKP wrote the first draft of the manuscript. SR, EP, and SG critically revised the manuscript. All authors contributed to manuscript revision, read, and approved the submitted version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.