Fetal haemoglobin production and the sickle gene in the oases of Eastern Saudi Arabia.

Fetal haemoglobin (HbF) levels have been measured in 137 normal (AA) subjects, 109 with the sickle-cell trait (AS) and 237 with sickle-cell anaemia (SS) from the oasis population of Eastern Saudi Arabia. In addition the proportion of F-cells has been estimated in 71 AA, 51 AS and 34 SS subjects. The mean HbF% (and the range of F-cells %) were: AA 0.77 (0.3--18), AS 1.38 (2.3--43) and SS 25.56 (33--98). The distribution of Hb F was always heterocellular. The influence of pregnancy accounts for most of the excess female subjects with sickle-cell trait showing raised Hb F and F-cells. Whilst the normal Arabs and those with sickle-cell trait did not differ from comparable groups of American blacks, both the % Hb F and % F-cells in Saudi Arabian patients with sickle-cell anaemia were much higher than in Blacks. The high Hb F levels in individuals with sickle-cell anaemia are not due to coexistent glucose-6-phosphate dehydrogenase deficiency or alpha-thalassaemia trait, and the Hb F level showed an inverse correlation with the degree of haemolysis. These findings indicate that the unusually elevated levels of Hb F are not due to an associated high frequency of a gene for hetero-cellular hereditary persistence of fetal haemoglobin in the oasis population, but rather from a genetically determined absolute increase in Hb F production related in some way to the SS genotype.