Five haplotypes in Black beta-thalassaemia heterozygotes: three are associated with high and two with low G gamma values in fetal haemoglobin.

Genotypes at seven different polymorphic restriction sites (5' to the epsilon gene, at the G gamma, at the A gamma, at the psi beta, 3' to the psi beta, at the beta, and 3' to the beta genes) were analysed by restriction endonuclease mapping of the DNA from 66 Black beta-thalassaemia heterozygotes from Georgia and several of their normal relatives. Five different haplotypes were observed. Three of these were associated with high G gamma values in the small amount of Hb F (0.8-8.3%) present in the blood of these patients and two with low G gamma values. One haplotype [- + - + + + +] that occurred on two of every three beta thalassaemia chromosomes was associated with high G gamma levels, and is the same as that found in some Black SS patients also having high G gamma values (Gilman & Huisman, 1984). Two others [- + + - + - +] and [- + - - + + +] were also associated with high G gamma, while two [- - - - + + +] and [+ - - - - + +] were associated with low G gamma. Variation in haematological data, mainly MCV and MCH values, was found to be caused in part by the type of beta-thalassaemia (defined by its haplotype) and by the presence of an additional alpha-thalassaemia-2 heterozygosity or homozygosity.