The molecular basis of alpha thalassaemia in a South African population

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Abstract
The molecular basis of .alpha. thalassemia was investigated in the so-called Cape Colored population of Cape Town. DNA from 17 cases was analyzed by Southern blotting and hybridization with an .alpha. globin complementary DNA probe. Three types of .alpha. thalassemia genetic determinants were detected: the 3.5 kb [kilobase] deletion which inactivates one .alpha. globin gene per chromosome (-.alpha./haplotype), a much larger deletion which removes both .alpha. globin genes (--/haplotype), and a non-deletion determinant which leaves both .alpha. globin genes intact. The interaction of these determinants with each other or with the normal chromosome (.alpha..alpha./)produced the phenotypes .alpha. thalassemia silent carrier, .alpha. thalassemia trait and Hb H disease. All cases of the -.alpha./haplotype result from the rightward deletion which removes the Bgl II site between the duplicated .alpha. globin genes. The predominance of the -.alpha./haplotype (21 out of the 28 .alpha. thalassemia determinants) over --/haplotype is consistent with the low incidence of Hb H disease and the apparent absence of Hb Bart''s hydrops fetalis in this population group.