β Thalassemia Associated with Increased HB F Production. Evidence for the Existence of a Heterocellular Hereditary Persistence of Fetal Hemoglobin (Hpfh) Determinant Linked to β Thalassemia in a Southern Italian Population

A family has been observed in which a β thalassemia determinant is inherited over three generations together with high Hb F level (8-12 %) and increased number of fetal-hemoglobin-containing-cells (F-cells). The values of red cell indices and globin chain synthesis ratios, yet typical of β thalassemia, were significantly shifted to the normal values when compared with those of typical β thalassemia heterozygotes belonging to the same family group. The occurrence in these individuals of a heterocellular hereditary persistence of fetal hemoglobin (HPFH) determinant and its linkage relationship with the β thalassemia is discussed. In the third generation two adult individuals were β thalassemia homozygotes having inherited a β thalassemia determinant from one parent and a β thalassemia together with the HPFH determinant from the other. They showed an extremely mild clinical condition, and 11-12 g/dl of mainly Hb F without having ever required blood transfusions. Virtually all the red cells were F-cells in both subjects. The importance of the coexistence of HPFH determinants capable of increasing the size of the F-cell population in patients affected by homozygous thalassemia is discussed, considering the sensible benefit which derives from enhanced Hb F production in this syndrome.