Consanguinity and the genetic control of Down syndrome

Eighty-three infants and children with a professional diagnosis of Down syndrome were studied cytogenetically. The results showed that 81.9% of them were trisomy 21 and 18.1% were the 46/47 + G type of mosaic. All cases were distributed according to parental consanguinity. The results showed that 77.9%, 16.2% and 5.9% of the trisomy 21 cases, and 53.3%, 26.7% and 20.0% of the mosaic cases were from non-consanguineous, first-cousin and second-cousin marriages, respectively. By combining all the cases, these percentages were 73.5%, 18.1% and 8.4%, respectively. Considering the high rate of inbreeding in Iraq (inbreeding coefficient = 0.0225) and using various statistical comparisons, these results revealed the lack of evidence for genetical control of non-disjunction in man.