The major concern in ruling out Hb D beta-zero thalassemia is that homozygous Hb D disease causes mild hemolytic anemia, but coinheritance of beta-zero thalassemia seems to produce deleterious effects relating to the presentation of Hb D disease, thus leading to chronic hemolytic anemia of moderate severity.21 This evidence concerns the gene GSTM1 and beta-thalassemia major.