Absence of Cis Delta Chain Synthesis in (δ β) Thalassemia (F-thalassemia)

(δ β) thalassemia or F-thalassemia is characterized by a thalassemic blood picture, elevated hemoglobin F, and normal hemoglobin A₂.

A family with (δ β) thalassemia is reported in which the propositus was a mixed heterozygote for (δ β) thalassemia and hemoglobin B₂. There was complete absence of hemoglobin A₂, indicating that this (δ β) thalassemia mutation completely suppressed the cis delta gene. The remaining normal delta gene was capable of increasing delta chain synthesis sufficiently to bring the hemoglobin A₂ to within normal range. These findings account for the absence of elevated hemoglobin A₂ in this form of thalassemia and demonstrate that (δ β) thalassemia is an entity genetically distinct from A₂ thalassemia. The possible genetic mechanisms of (δ β) thalassemia are discussed.