Cytogenetic profile in 1,921 cases of trisomy 21 syndrome.
BACKGROUND AND AIMS
Trisomy 21 is the most frequent genetic cause of intellectual disability. It is caused by different cytogenetic aberrations: free trisomy, Robertsonian translocations, mosaicism, duplication of the critical region and other structural rearrangements of chromosome 21. The aim of the study was to identify in Mexican trisomy 21 patients who attended Hospital Infantil de México Federico Gómez from 1992-2011 the type and frequency of the cytogenetic aberration and to evaluate the effect of maternal age.


METHODS
A retrospective analysis of epidemiological data and karyotype reports were carried out; type and frequency of the cytogenetic variants were determined.


RESULTS
We identified 2,018 cases referred with a clinical diagnosis of trisomy 21. In 1,921 analyses (95.2%) a cytogenetic variant of trisomy 21 was identified: free trisomy 21 in 1,787 cases (93.02%), four cases (0.21%) had an additional non-contributory aberration; Robertsonian translocations in 92 cases (4.79%); mosaicism in 31 cases (1.61%) and seven cases (0.36%) had other chromosomal abnormalities, five (0.26%) had other contributory structural rearrangements and two corresponded to double aneuploidies (0.10%). Gender distribution was 1,048 (54.56%) males and 873 (45.44%) females. A maternal age effect was observed in patients with free trisomy 21 with mothers >36 years of age.


CONCLUSION
The present work reports the experience of a Mexican referral center regarding the karyotype diagnosis of patients with trisomy 21 and is one of the most extensive studies published so far. Percentages of the cytogenetic abnormalities present in our population reflect the ones previously reported for these cytogenetic alterations worldwide.
['Flores-Ramírez|Francisco|F|', 'Palacios-Guerrero|Claudia|C|', 'García-Delgado|Constanza|C|', 'Morales-Jiménez|Ariadna Berenice|AB|', 'Arias-Villegas|Christian Martín|CM|', 'Cervantes|Alicia|A|', 'Morán-Barroso|Verónica Fabiola|VF|']
D000293:Adolescent D000328:Adult D002648:Child D002675:Child, Preschool D003582:Cytogenetics D004314:Down Syndrome D005260:Female D006801:Humans D007223:Infant D007231:Infant, Newborn D059785:Karyotype D008297:Male D008423:Maternal Age D012189:Retrospective Studies D055815:Young Adult
Trisomy 21 Robertsonian translocation Mosaicism Chromosome 21 Down syndrome