A cytogenetic study of a mentally retarded population in South Africa.

The entire population of the Umgeni Waterfall Institution for mentally retarded Whites was karyotyped using aceto-orcein and ASG banded preparations. Of the 512 subjects, 376 were males and 136 were females. Their ages ranged from 1 to 72 years and mental retardation ranged from borderline to profound. Altogether 11,1% had chromosome abnormalities, of which 8,2% had trisomy-21, 1,9% had other autosome abnormalities, and sex chromosome anomalies occurred in 1%. Normal variant chromosomes were seen in 4,5% of the population. Problems that arose in the course of the survey were mainly due to inadequate family histories and the high proportion of cases in which contact with the family had been lost, thus precluding proper follow-up studies.