Different hematologic phenotypes are associated with the leftward (-α4.2) and rightward (-α3.7) α+-thalassemia deletions

Abstract

We have compared the phenotypes of the two common deletion forms of α+-thalassemia by analysis of umbilical cord blood samples from Melanesia. Homozygotes for the leftward, 4.2-kilobase, deletion (-α4.2) had significantly higher levels of Hb Bart's at birth than homozygotes for the rightward, 3.7-kilobase, deletion (-α3.7). Compound heterozygotes for each deletion had intermediate values. Although deletion forms of α0 thalassemia were not found in this survey, nondeletion α-thalassemia was present at low frequency. Since the predominant rightward deletion in this population, -α3.7III, entirely removes the α1-gene and the 4.2-kilobase deletion deletes the α2-gene, these data indicate that the α2-globin gene has a higher output than the α1-gene, on single α-gene chromosomes.