An anomaly in the inheritance of haptoglobin types in Down's syndrome: a study of mother-child pairs.

A sample of 95 mother-child pairs provided evidence that plasma haptoglobin (Hp) types are inherited in an unusual manner by children with Down's syndrome. Homozygous mothers gave birth to more homozygotes and fewer heterozygotes than expected. Among offspring of heterozygous mothers, the frequencies were distributed essentially as expected. No abnormality was found in a normal control sample of 151 mother-child pairs. Using this material it was demonstrated that the anomalous Hp inheritance in Down's syndrome was not due simply to an increase in maternal age when the children were born.