EXTENDED GENE DIVERSITY AT TIRE FMR1 LOCUS AND NEIGHBORING CA REPEATSIN A SUB-SAHARAN POPULATION

We report on the allele distributions in a normal black African popula tion at two microsatellite loci neighbouring the FRAXA locus and at th e CGG repeat in the 5' end of the FMR-1 gene, which causes the fragile X syndrome. The CGG repeat distribution was found to be similar to th at of other ethnic groups, as well as to that of other non-human prima tes, possibly predicting a comparable prevalence of fragile X in Afric a. Significant linkage disequilibrium has been observed between fragil e X mutations and alleles of the DXS548 and FRAXAC1 loci in European a nd Asian populations, and some founder chromosomes may be extremely ol d, Those associated with FRAXAC1-A and DXS548-2 alleles are not presen t in the Asian fragile X samples, We searched for these alleles and th eir frequency in the well defined Bamileke population of Cameroon. All previously described alleles and some new ones were found in this sam ple, supporting the hypothesis of their pre-existence and subsequent l oss in Asian populations, Finally, the heterozygosity of the Bamileke sample was significantly higher at both marker loci and comparable to that of Europeans at the CGG repeat, confirming the notion that geneti c diversity is greater in Africans than in other groups and supporting the view that evolution of modern man started in Africa. (C) 1996 Wil ey-Liss, Inc.