(delta beta) zero thalassemia of the Southern Italian type. Its geographical origin and interaction with the sickle cell gene.

Hematological phenotypes and molecular defects were compared in 11 examples of heterozygous (delta beta) zero thalassemia. Despite differences in ethnic origins all cases had the gene deletion that is found in (delta beta) zero thalassemia of the Southern Italian type. HbF levels in these patients ranged from 3.6-14.6% with a mean +/- 1 SD of 8.9 +/- 3.1%. Variability in HbF output would suggest that additional factor(s) apart from deletions within the beta globin complex are involved in regulation of gamma gene expression. One individual, a compound-heterozygote for (delta beta) zero thalassemia and HbS, presented with a sickling disorder. Reduced HbF production in family members who are heterozygotes for (delta beta) zero thalassemia may explain the clinical picture in this instance.