Cytogenetic analysis of 1572 cases of Down syndrome: a report of double aneuploidy and novel findings 47,XY, t(14;21)(q13;q22.3)mat,+21 and 45,XX,t(14;21) in an Indian population.

Background: Down syndrome (DS) is the most common genetic reason for learning disability and congenital malformations in the human population, occurring with an incidence of 1 in 650-1000 newborns.

Objective: The aim of this study was to perform chromosome analysis in suspected DS cases with clinical features such as dysmorphism, epicanthic folds, simian crease, and hypotonia, referred to Super Religare Laboratories, Mumbai, India.

Methodology: Cytogenetic analysis of peripheral blood lymphocyte cultures was performed at 550-band level using the modified standard protocol.

Results: In this study, male:female sex ratio of DS patients was found to be 1.84:1. Among 1572 cases of DS, standard trisomy 21 in 1400 (89.05%) cases, Robertsonian translocation in 111 (7.06%) cases, and Mosaic form in 28 (1.78%) cases were observed. Three cases of double aneuploidy mos 47,XY,+21/47,XXY and one case of mosaic double aneuploidy mos 47,XY,+21/48,XXY,+21 were noticed. In addition, two novel findings 47,XY,t(14;21)(q13;q22.3)mat,+21 and 45,XX,t(14;21) with DS features are presented.

Conclusion: In this study, 1572 cases were confirmed as DS, of which maximum cases showed standard trisomy 21. Parental karyotyping and genetic counseling were recommended for the cases confirmed as DS after chromosome analysis.