Evidence for multiple origins of the beta E-globin gene in Southeast Asia.

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Abstract
To investigate whether recurrent mutation contributed to the high frequency of the .beta.E-globin gene in people of Southeast Asia, the haplotypes at 3 polymorphic restriction sites within and to the 3'' side of the .beta.-globin gene were used to predict the framework of 23 .beta.E-globin genes. These haplotypes suggested that .beta.E-globin genes are present in 2 different .beta.-globin gene frameworks. DNA sequence determination of one gene representing each framework demonstrated that the same mutation (GAG .fwdarw. AAG at codon 26) was present in both frameworks. The frameworks differed at 3 nucleotide positions known to be polymorphic in Mediterraneans. These polymorphic sites are located 70 nucleotides to the 5'' side of the .beta.E mutation and 382 and 1032 nucleotides to the 3'' side of it. The existence of the .beta.E mutation in these 2-.beta.-globin gene frameworks can be explained by recurrent mutation giving rise to .beta.E-globin, a double crossing-over-event, or 2 single crossing-over events. The 1st alternative, recurrent mutation of G .fwdarw. A at the first nucleotide of codon 26, seems most likely.