The comparatively low level of population structure has further contributed to GWA successes in Europeans through the utility of the HapMap CEU panel, the “CEPH European” collection of 30 European-American families genotyped at high density by the International Haplotype Map Project33,34. Early GWA studies used a tag-SNP approach 33,35,36, in which each SNP in a genome-wide subset of SNPs was tested for disease association. It was hoped that each true disease SNP not genotyped in a study would be “captured” through a minimal level of statistical association, or linkage disequilibrium (LD)37,38,39, with an informative nearby tag SNP included among the genotyped SNPs. The existence of a true disease SNP in an association study would then be detectable through separate associations of the disease SNP and the phenotype with the tag SNP.
