Age-dependency of somatic selection in South African Negro G-6-PD heterozygotes.

The distribution of red cell G-6-PD phenotypes was analysed in terms of their manifestation in South African Negro females of different age classes. It was found that with increasing chronological age, over the age range from the teens to adulthood, the relative proportion of females expressing a "non BB" phenotype gradually decreases and the relative proportion of females expressing a "B" phenotype increases concomitantly. It is suggested that this phenomenon is attributable to age-dependent somatic selection against the deficient A- cell line in appropriate heterozygotes. This process can give rise to the misinterpretation of recording a growing excess of "homozygotes" and a corresponding increasing deficit of "heterozygotes" with ongoing chronological ageing. It is speculated that the postulated process of age-dependent somatic selection may be in response to malaria as the underlying selective agent. Considerations in this respect are discussed in greater detail.