Origin and Spread of β-Globin Gene Mutations in India, Africa, and Mediterranea: Analysis of the 5\u27 Flanking and Intragenic Sequences of β^S and β^C Genes

Nucleotide polymorphisms of both the 5\u27 flanking and intragenic regions of the human β-globin gene were investigated by directly sequencing genomic DNA after amplification by the polymerase chain reaction in 47 subjects homozygous for the β^s or the β^c mutation. The sickle-cell mutation was found in the context of five different haplotypes defined by eight nucleotide substitutions and various structures of a region of the simple repeated sequence(AT)x Ty. All subjects from the same geographic origin bear an identical chromosomal structure, defining the Senegal-, Bantu-, Benin-, Cameroon-, and Indian-type chromosomes. These results strengthen our previous conclusions about the multiple occurrence of the sickle-cell mutation. The Benin-type chromosome was also found among Algerian an d Sicilian sickle-cell patients, whereas the Indian-type chromosome was observed in two geographically distant tribes, illustrating the spread of these sickle-cell genes. We also found that the intragenic sequence polymorphisms (frameworks) are not always in linkage disequilibrium with the Bam H I polymorphism downstream from the β-globin gene, as h ad been previously observed. Finally, we present a tentative phylogenetic tree of the different alleles at this locus. Some polymorphisms of this sequence might be contemporary with our last common ancestor, the great apes, that is, about 4 -6 millions years old