Down's syndrome in Hyderabad, India.

A cytogenetic analysis of Down's syndrome revealed straight trisomy 21 in 96.5 per cent affected. Remaining 3.5 per cent were found to have chromosomal mosaicism. In addition, a normal karyotype was observed in 2 individuals with Down's phenotype. A survey of Down's syndrome in Hyderabad gave an incidence of 1.17 per 1000 or 1 in 853 live births. There was a significant increase in the mean maternal age of the affected over the controls. Sex ratio was also higher in our sample of Down's syndrome as compared to the general population.