The Negro variety of hereditary persistence of fetal haemoglobin is a mild form of thalassaemia.

Further studies have been carried out on blood of the 15-year-old Negro male from Baltimore who was the first reported case of the homozygous state for hereditary persistence of fetal haemoglobin. His red cells contain only Hb F; Hbs A and A2 have never been detected. Over a 15-year period of follow up the red cells of this individual have shown persistent microcytosis with reduced MCH and MCV values. His whole-blood p50 value is decreased, probably because of lack of interaction between Hb F and 2,3-diphosphoglycerate. However, his haemoglobin level at the age of 15 years is lower than would be predicted from the degree of increased oxygen affinity. Globin-chain synthesis studies suggest that this is because he has a mild thalassaemia disorder with an alpha/gamma-chain production ratio of about 1.5, similar to that found in beta-thalassemia heterozygotes. Thus Negro HPFH appears to be a well-compensated form of delta beta thalassaemia.