Distribution of Sickle-cell Hæmoglobin in Saudi Arabia

Abstract

IT is now recognized that the sickle-cell trait, though inherited through a single gene, does not necessarily maintain a constant frequency in a population from, generation to generation, but that its frequency is the result of two opposing processes of natural selection. The gene for sickle-cell hæmoglobin (or hæmoglobin S) tends to be eliminated from the population because of the deaths of homozygotes from sickle-cell anæmia, while, in the presence of endemic falciparum (malignant tertian) malaria, homozygotes for normal adult hæmoglobin (hæmoglobin A) have a higher mortality than heterozygotes with genes for both A and S. The sickle-cell gene is thus maintained from generation to generation from the pool represented by the favoured heterozygotes. So long as malarial incidence remains constant, a state of balanced polymorphism will eventually be reached; but if the former then changes, there will be a gradual shift towards a new balance of genes. There can, therefore, be no doubt that the frequency of the sickle-cell trait in a population is, at least in part, related to the recent malarial history of that population.