The Genetic Basis of Hb Q‐H Disease

A Chinese family has been studied in which two siblings have haemoglobin Q‐H disease. Using a combination of haematological and haemoglobin analysis, globin chain synthesis, analysis of α/β globin messenger RNA ratios and restriction endonuclease mapping, it has been shown that each of these siblings has received one chromosome on which both α chain genes have been deleted and another on which there is only a single α chain locus which carries the αQ mutation. Their genotype is thus ——/—αQ. Despite the fact that the haemoglobin Q mutation in this family is carried on a chromosome with a single α chain locus, heterozygous carriers for the variant have only 25% or less haemoglobin Q. Our observations indicate that the molecular basis for haemoglobin Q‐α thalassaemia is similar to that for the common form of haemoglobin H disease in Orientals. Furthermore, they provide clear evidence that the level of an α chain variant in heterozygous carriers is not a reliable reflection of the number of α globin genes.