Red cell polymorphisms in Down's syndrome. Gene frequencies and phenotype associations.

Abstract

The phenotype frequencies of red cell phosphoglucomutase (PGT), acid phosphatase (ACP), adenylate kinase (AK), 6‐phosphogluconate dehydrogenase (PCD), adenosine deaminase (ADA), alanine aminotransferase (ALA), isocitric dehydrogenase (ICD) and glucose‐phosphate dehydrogenase (G‐6‐PD) and the ABO blood groups were investigated in a group of 256 subjects with Down's syndrome and 409 subjects with mental retardation but without chromosomal defects. The estimates and standard errors of the gene frequencies, deviations from the Hardy‐Weinberg law and between‐group comparisons by Haldane's log ratio test were determined.G‐tests were carried out between all systems to detect any phenotype association, and gene‐counting and subsequent G‐tests were performed to investigate possible gene associations. During these association tests, data presented elsewhere on haptoglobin (Hp) and group specific proteins (Gc) were included.No inter‐group differences could be detected, but positive associations between PGT and ACP were found in the Down's group and for Hp vs. ADA and Hp vs. ACP in the control group.A sex difference was found in the PGT phenotypes in the Down's subjects, principally in the age range 0–18 years, and an excess of type B in the ABO groups of the Down's subjects was observed.Three examples of rare variants were observed in the Down's subjects, one example of the PGT2 type 3:1, one subject with a G‐GPD type A and one subject with a variant PGI) phenotype not reported previously.