Cytogenetic studies of 1001 Down syndrome cases from Andhra Pradesh, India

Cytogenetic data obtained from investigating 1001 patients of Down syndrome (DS) and their parents over a period of 20 years (January 1979 - January 1 999) are presented. The frequency of pure trisomy, mosaicism and translocat ion was 87.92, 7.69 and 4.39 per cent respectively. The origin of the extra chromosome 21 due to meiotic non-disjunction was 79.24 per cent maternal a nd 20.76 per cent paternal. A high frequency of acrocentric chromosome asso ciations was also observed in mothers of children of Down syndrome, this mi ght have predisposed to an enhanced risk for non-disjunction. Birth order o f DS showed a higher number of first and second horns. Reproductive perform ances of the parents indicated a high rate of abortions, compared to contro ls. Cytogenetic investigations carried out over these years greatly helped in the management of these children and for counseling the affected familie s.