Cytogenetic investigations in Down syndrome patients & their parents.

A total of 1343 mentally retarded patients referred for cytogenetic evaluation were studied. Of these Down syndrome was confirmed in 365 (21.17%). There were 316 patients of trisomy 21 (86.58%); 21 of mosaicism (5.75%) and 28 of translocation (7.67%). Trisomy 21 patients with chromosomal variants were observed in 17 (4.65%). A 1.37:1 male:female ratio was seen. Karyotyping was also done on 182 parents (of patients of mosaic Down, translocation Down and trisomy 21 with chromosomal variants and in parents with suspected low mosaicism). Mosaic trisomy 21 cell line was found in one mother (0.27%); 6 parents (1.65%) were seen to be translocation carriers and 7 had chromosomal variants (1.92%). Cytogenetic investigations help to give appropriate genetic counselling to patients and their families.