Frequency and origins of hemoglobin S mutation in African-derived Brazilian populations

Abstract

Africans arrived in Brazil as slaves in great numbers, mainly after 1550. Before the abolition of slavery in Brazil in 1888, many communities, called quilombos, were formed by runaway or abandoned African slaves. These communities are presently referred to as remnants of quilombos, and many are still partially genetically isolated. These remnants can be regarded as relicts of the original African genetic contribution to the Brazilian population. In this study we assessed frequencies and probable geographic origins of hemoglobin S (HBB*S) mutations in remnants of quilombo populations in the Ribeira River valley, São Paulo, Brazil, to reconstruct the history of African-derived populations in the region. We screened for HBB*S mutations in 11 quilombo populations (1,058 samples) and found HBB*S carrier frequencies that ranged from 0% to 14%. We analyzed beta-globin gene cluster haplotypes linked to the HBB*S mutation in 86 chromosomes and found the four known African haplotypes: 70 (81.4%) Bantu (Central Africa Republic), 7 (8.1%) Benin, 7 (8.1%) Senegal, and 2 (2.3%) Cameroon haplotypes. One sickle cell homozygote was Bantu/Bantu and two homozygotes had Bantu/Benin combinations. The high frequency of the sickle cell trait and the diversity of HBB*S linked haplotypes indicate that Brazilian remnants of quilombos are interesting repositories of genetic diversity present in the ancestral African populations.