A novel α-globin gene arrangement in man

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Abstract
The human genome has two linked α-globin genes on chromosome 16. Deletion of one or more of them, as occurs in α-thalassaemia, leads to a reduced output of α-globin mRNA in proportion to the number of α-globin genes lost1. In some racial groups deletion of one of the pair of α-globin genes may result from unequal crossing over between the genes on homologous chromosomes2,3 by a mechanism resembling that postulated for the formation of the δβ fusion genes of the Lepore haemoglobins4. By analogy, the opposite chromosome in this cross-over should have three α-globin genes just as the ‘anti-Lepore’ chromosome has three non-α-chain genes. We describe here a Welsh family in which three members have five α-globin genes—three on one chromosome and two on the other. The additional α gene results in an increased α mRNA output and it may therefore produce the phenotype of mild β-thalassaemia.