A de novo variant in ADGRL2 suggests a novel mechanism underlying the previously undescribed association of extreme microcephaly with severely reduced sulcation and rhombencephalosynapsis.
Extreme microcephaly and rhombencephalosynapsis represent unusual pathological conditions, each of which occurs in isolation or in association with various other cerebral and or extracerebral anomalies. Unlike microcephaly for which several disease-causing genes have been identified with different modes of inheritance, the molecular bases of rhombencephalosynapsis remain unknown and rhombencephalosynapsis presents mainly as a sporadic condition consistent with de novo dominant variations. We report for the first time the association of extreme microcephaly with almost no sulcation and rhombencephalosynapsis in a fœtus for which comparative patient-parent exome sequencing strategy revealed a heterozygous de novo missense variant in the ADGRL2 gene. ADGRL2 encodes latrophilin 2, an adhesion G-protein-coupled receptor whose exogenous ligand is α-latrotoxin. Adgrl2 immunohistochemistry and in situ hybridization revealed expression in the telencephalon, mesencephalon and rhombencephalon of mouse and chicken embryos. In human brain embryos and fœtuses, Adgrl2 immunoreactivity was observed in the hemispheric and cerebellar germinal zones, the cortical plate, basal ganglia, pons and cerebellar cortex. Microfluorimetry experiments evaluating intracellular calcium release in response to α-latrotoxin binding showed significantly reduced cytosolic calcium release in the fœtus amniocytes vs amniocytes from age-matched control fœtuses and in HeLa cells transfected with mutant ADGRL2 cDNA vs wild-type construct. Embryonic lethality was also observed in constitutive Adgrl2-/- mice. In Adgrl2+/- mice, MRI studies revealed microcephaly and vermis hypoplasia. Cell adhesion and wound healing assays demonstrated that the variation increased cell adhesion properties and reduced cell motility. Furthermore, HeLa cells overexpressing mutant ADGRL2 displayed a highly developed cytoplasmic F-actin network related to cytoskeletal dynamic modulation. ADGRL2 is the first gene identified as being responsible for extreme microcephaly with rhombencephalosynapsis. Increased cell adhesion, reduced cell motility and cytoskeletal dynamic alterations induced by the variant therefore represent a new mechanism responsible for microcephaly.
['Vezain|Myriam|M|', 'Lecuyer|Matthieu|M|', 'Rubio|Marina|M|', 'Dupé|Valérie|V|', 'Ratié|Leslie|L|', 'David|Véronique|V|', 'Pasquier|Laurent|L|', 'Odent|Sylvie|S|', 'Coutant|Sophie|S|', 'Tournier|Isabelle|I|', 'Trestard|Laetitia|L|', 'Adle-Biassette|Homa|H|', 'Vivien|Denis|D|', 'Frébourg|Thierry|T|', 'Gonzalez|Bruno J|BJ|', 'Laquerrière|Annie|A|', 'Saugier-Veber|Pascale|P|0000-0001-5601-3415']
D000328:Adult D000818:Animals D002453:Cell Cycle D002478:Cells, Cultured D002642:Chick Embryo D004252:DNA Mutational Analysis D004622:Embryo, Mammalian D005260:Female D005333:Fetus D018507:Gene Expression Regulation, Developmental D005865:Gestational Age D006801:Humans D008297:Male D051379:Mice D008810:Mice, Inbred C57BL D008822:Mice, Transgenic D008831:Microcephaly D008875:Middle Aged D009154:Mutation D009457:Neuroglia D043562:Receptors, G-Protein-Coupled D012249:Rhombencephalon
ADGRL2 Rhombencephalosynapsis Adhesion-GPCR Alpha-latrotoxin Human extreme microcephaly LPHN2