SLE prevalence varies substantially by ethnic ancestry: African-Americans have a 3 to 5 fold increased risk of SLE compared to individuals with European ancestry [29], [30], [31]. Earlier studies report association between PTPN22 and SLE, primarily with the non-synonymous variant rs2476601 in European-derived populations. However, the frequency of this disease-associated SNPs varies strongly among Europeans based on geographic region, with a higher prevalence in Northern European countries relative to Southern European populations [32], [33]. Additionally, rs2476601 is either monomorphic or extremely rare in the Japanese population and only rarely observed among the admixed African-American population [32].
