Objective: An association of single-nucleotide polymorphisms (SNPs) in the FAM167A (previously referred to as C8orf13)-BLK region with systemic lupus erythematosus (SLE) has been demonstrated in Caucasians and in Asians. Recent studies have shown that many genes, including IRF5, STAT4, and PTPN22, are shared susceptibility genes in multiple autoimmune diseases. We undertook the current study to examine whether the FAM167A-BLK region is also associated with susceptibility to systemic sclerosis (SSc).
Methods: Japanese patients with SSc (n = 309) and healthy controls (n = 769) were enrolled in a 2-tiered case-control association study. In tier 1, 124 patients and 412 controls were tested to determine association of 16 tag SNPs encompassing the FAM167A-BLK region with SSc. In tier 2, an additional 185 patients and 357 controls were analyzed for SNP rs13277113.
Results: Two haplotype blocks that correspond approximately to FAM167A and BLK were observed. In tier 1 of the study, the rs13277113A allele in the BLK block exhibited the most significant association with SSc after correction for multiple testing (permutated P = 0.024). Two SNP haplotypes formed by rs13277113 and the most significant SNP in the FAM167A block did not exhibit stronger association. When samples from tier 1 and tier 2 were combined, the rs13277113A allele was significantly associated with SSc (odds ratio 1.45 [95% confidence interval 1.17-1.79], P = 6.1 x 10(-4)). Association or a tendency toward association of rs13277113A with SSc was observed regardless of a patient's autoantibody profile or whether a patient had diffuse cutaneous or limited cutaneous SSc.
Conclusion: Our findings indicate that the rs13277113A allele is associated not only with SLE but also with SSc and that the FAM167A-BLK region is a common genetic risk factor for both SLE and SSc.