Blood groups and diseases

Abstract

The ABO blood group system, and most other systems of hereditary blood factors, show wide differences in gene frequency between one population and another. Much of the variation found is probably due to random effects, but much also is almost certainly due to natural selection, certain phenotypes being more liable than others to suffer from certain diseases, with resulting loss of fertility. Most investigations have been based on determining the frequency of certain factors in those suffering from particular diseases. Thus, for instance, patients with carcinoma of the stomach have a raised frequency of blood group A, almost certainly because people of this group have a raised susceptibility to the disease. Several other established cases, and many other probable cases are known of such associations. Numerous examples have recently been discovered of associations of diseases with particular histocompatibility antigens. It is suggested that the gene frequencies in many if not most genetic polymorphisms are the result of an equilibrium, varying with locality, between the selective effects of different diseases and other environmental stresses on the various phenotypes of any given system.