Genetic counseling and genetic heterogeneity in the thalassemias.

In this study, we have compared the hemoglobin A2 levels (Hb A2) of alpha-thalassemia carriers (-alpha/-alpha and -alpha/alpha alpha genotypes) with those of double heterozygotes for delta+ and beta thalassemia genes, who were identified by family studies and polymorphic restriction site analysis within the beta-globin gene cluster. We found that double heterozygotes for the delta+ and beta thalassemia have significantly (p less than 0.001) higher Hb A2 levels as compared with carriers of alpha-thalassemia. This finding has practical implications in the genetic counseling of subjects with a thalassemia-like phenotype associated with normal or borderline Hb A2 levels.