Severity ranking of non-deletional alpha thalassemic alleles: insights from an Omani family study

In an Omani family, four different alpha thalassemic alleles, one single-gene deletional (-α(3.7) ) and three non-deletional forms (α(TSaudi) , α(Δ5nt) , and α(ΔG) ), interact in various combinations and result in two distinct hematological phenotypes, with and without HbH inclusions. After excluding the presence of potential genetic modifiers, viz associated β-thalassemic alleles or functional alpha hemoglobin stabilizing protein (AHSP) polymorphisms, we observed that only the genetic combinations involving α(TSaudi) mutation are associated with HbH inclusions (a marker of degree of α/β-chain imbalance) and high reticulocyte count (a marker of ongoing hemolysis). Overall, the α(TSaudi) mutation is associated with a more severe α-globin deficiency than the other two (α(Δ5nt) and α(ΔG) ) non-deletional α(0) thalassemic mutations. The likely molecular explanation is that the compensatory increase in the linked α1 globin gene expression is much more compromised in cases with α(TSaudi) mutation.