A mother-child segregation distortion for the Rh system. New evidence for another compatibility system associated with Rh.

In the maternity service of a private hospital in Santiago, Chile, 6,974 mother-infant pairs typed for the D-d alleles of the Rh system were collected. In our analysis, all the paris attended from October 1974 to December 1975 and from January 1977 to September 1979 were used. The segregation analysis, made by means of the T mother-child matrix, assuming Hardy-Weinberg equilibrium, reveals that: Rh(-) mothers have a higher rate of admission than do Rh(+) mothers; Rh(+) mothers produce fewer Rh(-) infants than expected; and, with less significance, Rh(-) mothers produce more Rh(+) infants than expected. This leads to a reduction in the proportion of dd individuals from mothers to their children. Ethnic subdivisions of the sample, the period considered, and the extension of the antiisoimmunization therapy do not seem to affect the general pattern of the distortion. The only plausible hypothesis to explain this finding is that selection is not related to the known Rh antigenic specificities. The reduction of the proportion of dd individuals in 1 generation leads us to review models on Rh polymorphism. It seems clear that no classical compensation is possible and d must disappear unless another mechanism maintains it in populations.