Prevalencia de mosaicismo para la trisomía 21 y análisis de las variantes citogenéticas en pacientes con diagnóstico de síndrome de Down: Revisión de 24 años (1986-2010) del Servicio de Genética del Hospital General de México ''Dr. Eduardo Liceaga''

Background. Down syndrome is the principal genetic cause of learning disabilities, with an incidence of 1/650 live births. Diagnosis is confi rmed by karyotyping. Chromosomal variants are important for genetic counseling. We determined the prevalence of cytogenetic variants in patients with clinically diagnosed Down syndrome in the Hospital General de Mexico Dr. Eduardo Liceaga and discussed its relevance according to maternal age. Methods. We reviewed karyotype data of patients with clinically diagnosed Down syndrome from January 1986 to December 2010 and obtained maternal and patient ages. Results. From 581 patients analyzed, 71 (12.22%) had normal karyotype. In 510 patients we confi rmed that 445 (87.3%) had a regular trisomy, 22 (6.3%) were the product of a Robertsonian translocation and mosaicism was found in 43 (8.4%) patients. Maternal age was higher in patients with regular trisomy (median: 30 years) and mosaicism (median: 29 years) than in those with translocations (median: 20 years). Conclusions. Characterization of chromosomal aberrations in Mexican Down syndrome patients allows us to offer appropriate genetic counseling and to establish the prevalence of mosaicism in our population, which was higher than the reported data. Cytogenetic analysis for detection of mosaicism is important in patients with scarce clinical data of Down syndrome or with learning disabilities of unknown origin.