Alpha-thalassemia is related to prolonged survival in sickle cell anemia

We have determined the frequency of deletional a-thalassemia in black populations in the USA and Africa that harbor sickle cell anemia. In normals, the frequency of the chromosome bearing a deletion of one of the two normal a gene loci, designated (-a), ranged from 0.12 to 0.16, and in sickle trait subjects, the frequency ranged from 0.18 to 0.20. By contrast, in sickle cell anemia subjects, the frequency was significantly greater and ranged from 0.22 to 0.33. Analysis demonstrated that the greater frequency in the last group was primarily a result of an increased number of subjects with a-thalassemia trait (also called homozygous a-thalassemia-2). In addition, the frequency of the (-a) chromosome was found to increase progressively with age, supporting the hypothesis that 1/2 a-thalassemia is favorable to the survival of subjects with sickle cell anemia. Thus, individuals who inherit a-thalassemia and sickle cell anemia may represent a subgroup of patients with a longer life expectancy.