The British form of hereditary persistence of fetal hemoglobin results from a single base mutation adjacent to an S1 hypersensitive site 5' to the A gamma globin gene.

The G gamma and A gamma genes of an individual homozygous for the British form of A gamma nondeletion hereditary persistence of fetal hemoglobin have been cloned and partially sequenced. The G gamma gene was normal, but the A gamma gene was found to have a single base change (T----C) at -198 bp relative to the cap site. Supercoiled plasmids containing normal gamma-genes or the mutant A gamma-gene displayed an S1-hypersensitive site immediately 5' to the base change.