Heterogeneity in the molecular basis of three types of hereditary persistence of fetal hemoglobin and the relative synthesis of the G? and A? types of ? chain

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Abstract
Restriction endonuclease analyses of DNA from one Black GγAγ-HPFH homozygote and four Black and one Indian GγAγ-HPFH heterozygotes have identified three different HPFH types which are the result of large deletions including the δ and β genes. Two of the types are comparable to those characterized previously, but the third, which is present in the Indian heterozygote, shows a distinct difference in the size of the deletion. The 5′ end point of the deletion in this type III GγAγ-HPFH extends 0.5–1.0 kb beyond the 5′ end point of one of the Black types of HPFH (type I). Each of the three types is associated with a distinct ratio between the Gγ and the Aγ chains, an observation supported by family data. The highest ratio is found in the heterozygote with the Indian type III GγAγ-HPFH, with 69.3% Gγ chains, while the averages for the other types were 50.7% Gγ (type I) and 32.3% Gγ (type II).