Distribution of genome-wide linkage disequilibrium based on microsatellite loci in the Samoan population.

Whole genome-wide scanning for susceptibility loci based on linkage disequilibrium (LD) has been proposed as a powerful strategy for mapping common complex diseases, especially in isolated populations. We recruited 389 individuals from 175 families in the US territory of American Samoa, and 96 unrelated individuals from American Samoa and the independent country of Samoa in order to examine background LD by using a 10 centimorgan (cM) map containing 381 autosomal and 18 X-linked microsatellite markers. We tested the relationship between LD and recombination fraction by fitting a regression model. We estimated a slope of -0.021 (SE 0.00354; p<0.0001). Based on our results, LD in the Samoan population decays steadily as the recombination fraction between autosomal markers increases. The patterns of LD observed in the Samoan population are quite similar to those previously observed in Palau but markedly contrast with those observed in a non-isolated Caucasian sample, where there is essentially no marker-to-marker LD. Our analyses support the hypothesis of a recent bottleneck, which is consistent with the known demographic history of the Samoan population. Furthermore, population substructure tests support the hypothesis that self-identified Samoans represent one homogenous genetic population.