Two different molecular organizations account for the single α-globin gene of the α-thalassemia-2 genotype

Abstract

The α-thalassemia-2 (α-thal-2) genotype or mild α-thalassemia gene consists of a single structural α-globin gene on the chromosome that normally bears two α-globin genes. The authors used blot hybridization to investigate variation in the molecular organization of this genotype and to determine the distributions of these variations in the world population. Two different patterns of gene organization responsible for the α-thal-2 genotype were found: the first was the result of a 4.2-kilobase pair deletion involving the normal 5' α-globin gene (leftward deletion α-thal-2 genotype), and the second probably the result of a crossover deletion of a DNA fragment bridging the two normal α-globin genes (rightward deletion α-thal-2- genotype). The rightward deletion was found in all 9 Black subjects, all 8 Mediterranean subjects, and 4 of 13 Chinese subjects. The leftward deletion was found and the nondeletion α-thalassemia lesion was found in five of the nine remaining Chinese subjects. It is likely that these deletions are related to specific DNA sequences that determine DNA recombinational events.