Different severity of homozygous beta-thalassemia among siblings

Different degrees of severity of anemia are presented in three siblings with homozygous beta-thalassemia. II-1, the most severely affected one, is splenectomized and needs frequent blood transfusion, while II-4 has mild anemia and never receives transfusion. II-3 has moderate anemia and mild jaundice and hepatosplenomegaly. Restriction endonuclease DNA mapping revealed the alpha-thalassemia-2 genes in II-3 and II-4 and no alpha-thalassemia-2 haplotype in II-1. Furthermore, II-4, who is mildly affected, is homozygous for alpha-thalassemia-2 whereas II-3 is an alpha-thalassemia-2 heterozygote. These observations indicate that concomitant inheritance of alpha-thalassemia can decrease the severity of beta-thalassemia.