Studies on the Proportion and Synthesis of Haemoglobin G Philadelphia in Red Cells of Heterozygotes, a Homozygote, and a Heterozygote for both Haemoglobin G and α Thalassaemia

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Abstract
The proportion of Hb G Philadelphia (.alpha.68-Asn .fwdarw. Lys) in heterozygotes has a well-defined bimodal distribution around means of 33% and 46% Hb G. Microcytosis and hypochromia are consistently associated with the latter group, who also have a decreased ratio of .alpha./.beta.-chain synthesis in the peripheral blood, but these characters are not linked to the Hb-G.alpha. gene, because a parent with microcytosis and 46% Hb G.alpha. may have offspring with 33% Hb G without significant microcytosis. In one family a subject with Hb G and Hb G2 but no Hb A or Hb A2 is presumably a homozygote for .alpha.G. This subject has microcytosis and a decreased ratio of .alpha./.beta. chain synthesis. In another family a subject with Hbs H, G and G2 but without Hbs A or A2 is heterozygous for both Hb G and .alpha. thalassemia I. The .alpha.G mutation may occur on a chromosome with only a single .alpha.-chain locus and the expression in heterozygotes as 46% or 33% Hb G is determined by the homologous chromosome in trans having either 1 or 2 normal .alpha.A genes, respectively. The significance of this polymorphism for chromosomes carrying .alpha.-chain genes is discussed.