We found eight SNPs, representing two chromosomal regions, for which the evidence of unusual population differentiation was genomewide-significant (nominal P-value<10−7, P-value<0.03 after correcting for 284,191 common SNPs tested). Six of the SNPs lie in or near the TLR (toll-like receptor) genes TLR10 and TLR1, while the other two lie inside the NADSYN1 (NAD synthesase 1) gene (http://genome.ucsc.edu/) (Table 3). For each of these SNPs, the allele frequency difference between Icelanders and Scots was greater than 15% (Table S1), far in excess of typical allele frequency differences of about 3% that correspond to an F ST value of 0.0020. Only two of the SNPs from Table 3 were present in Norwegian data based on the Affymetrix 6.0 chip (rs10024216 and rs11096957 in the TLR region), but for both of these SNPs—and also for rs7940244 in the NADSYN1 region (which was not genomewide-significant in the comparison of Icelanders and Scots)—allele frequency differences between Norwegians and Scots were likewise greater than 15% (Table S1), ruling out an effect specific to Icelanders. We also report frequencies of these SNPs in HapMap populations [27] (Table
