CHRISTMAS DISEASE COLOR-BLINDNESS AND BLOOD GROUP XGA

A large kindred, traced from 1736, in which Christmas disease and mild red-green color blindness was found to segregate, was studied by assays of blood clotting factor IX, by tests of color vision and by blood grouping. Forty-three male subjects were recognized as having Christmas disease with moderate to severe deficiencies of factor DC. No significant rise in the blood levels of factor DC with aging was noted in "non-bleeder" male subjects and only a suggestive rise was observed in female subjects. Segregation ratios were not, in contrast to previous reported studies, at variance with expected ratios. An increase in the number of children was observed in the families of bleeders and of heterozygous female subjects, contributing a source of additional Christmas disease genes to their family population. The Mary Lyon hypothesis is suggested as an explantation for the factor DC levels observed in heterozygous female subjects and extended to explain the levels of factor IX in their daughters and granddaughters, who are half-chance and quarter-chance heterozygotes, respectively. Linkage data relating to Christmas disease and deuteranopia suggests that these 2 gene loci are not close on the X chromosome. The variance of ABO blood groups in this family from the general population provides an example of genetic drift and the founder effect. The Xga blood group incidence shows a sex difference in a single kindred, as previously demonstrated in random populations.