The frequency of the A gamma T gene in the presence and absence of the beta S or beta C gene in the Black population of the Southeastern USA.
Quantitative information about the three types of gamma chains (A gamma T, A gamma I, G gamma) has been obtained for the Hb F from 285 normal Black babies, 172 babies with a Hb S or Hb C heterogeneity, and from 150 babies and older patients with the SS, SC, or CC conditions by means of a high pressure liquid chromatographic microprocedure. The frequency of the A gamma T gene in the AA babies was 0.1035, while that in the SS patients was a low 0.0362. This low A gamma T frequency in the SS population adequately explains the lower percentage (13.2%) of A gamma T heterozygotes among AS newborn babies as compared to 17.9% among AA babies. The genotype with the A gamma T mutant in trans to the beta S mutation is presumed to occur about three times more frequently than that in which the A gamma T mutant is in cis to the beta S mutation. A study of family members of one SS patients who has an A gamma T homozygosity provided data supporting linkage of the A gamma T and beta S anomalies in some Hb S heterozygotes.