Five haplotypes in Black β-thalassaemia heterozygotes: three are associated with high and two with low Gγ values in fetal haemoglobin

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