Because of the consistent association of a specific beta-thalassaemia mutation and normal Hb A2 levels, we postulate that this beta-thalassaemia chromosome carries a delta gene (delta-thalassaemia) which is unable to increase the delta-globin output in response to beta-thalassaemia.
The 7.2 kilobase (kb) Corfu deltabeta thalassemia mutation is the smallest known deletion encompassing a region upstream of the human delta gene that has been suggested to account for the vastly different phenotypes in hereditary persistence of fetal hemoglobin (HPFH) versus beta thalassemia.