A new genetic basis for hemoglobin-H disease.

We studied 11 families with alpha-thalassemia from the Qatif population of eastern Saudi Arabia to determine the genetic and molecular basis of hemoglobin-H disease, which is being encountered in this area with increasing frequency. The results show that there are two common alpha-thalassemia haplotypes, a deletion (-alpha/) determinant and a nondeletion (alpha alpha T/) determinant, which interact to produce a series of overlapping phenotypes. The most severe, hemoglobin-H disease, results from the homozygous state for the nondeletion determinant--a pattern of inheritance not previously recognized for this condition. Its molecular and genetic properties are thus different from those that produce the condition in Oriental or Mediterranean populations.