Unstable and thalassemic alpha chain hemoglobin variants: a cause of Hb H disease and thalassemia intermedia.

We report an update of the alpha-globin gene point mutations resulting in structural modification associated with an alpha-thalassemia (alpha-thal) phenotype. These variants, barely symptomatic in the heterozygous state, are either unstable due to folding defects and/or defects in binding to alpha-hemoglobin stabilizing protein (AHSP). This is predicted to result in precipitation of the unstable alpha chains or Hb variant, a concomitant decrease in the overall quantity of normal alpha-globin in the red cells and a potential degree of anemia and possibly, hemolysis. Genotype/phenotype correlation and potential genetic risk in combination with common or less common alpha-thal defects are discussed.