Cytogenetic Analysis of 584 Cases with Clinical Diagnosis of Down Syndrome

The cytogenetic types of Down syndrome, which is a widespread disease and the most common cause of mental retardation among live-borne babies, vary according to the risk of recurrance and has been a guide for the genetic counseling. This study was conducted between January 1996 and December 2006 in our department. The study included 584 patients with clinical diagnosis of Down syndrome. There were 232 (39.7%) female and 352 (60.3%) male patients. The aim of the study was to investigate the cytogenetic types and its incidence in this group of patients. By using peripheral blood culture method for cytogenetic analysis, it was found that 128 cases (21.9%) had normal karyotypes, whereas 456 (%78.1) cases had karyotype of Down syndrome. There was regular type in 432 patients (%94.7), translocation type in 14 (%3.1) [8 t(14;21), 6 t(21;21)], mosaic type in 4 (%0.9), and 6 patients (%1.3) associated with inv(9) with regular type karyotype in patients with Down syndrome. Four of 14/21 type of translocations were familial (50.0%) and other 14/21 and 21/21 types translocations were found to be de novo. The male to female ratio was 1.64: 1 (283 male:173 female), mean age of mothers was 34.25 ± 7.76 and of mothers having translocation type of Down syndrome, it was 28.29 ± 5.0.The results of this study point out the necessity of cytogenetic analysis for appropriate genetic counseling in establishing the clinical diagnosis of Down syndrome.