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Interferon regulatory factor 7 (IRF7) has an essential role in the production of type I interferon. Although recent studies detected association of a single nucleotide polymorphism (SNP) rs4963128 in PHD and ring finger domains 1 (PHRF1)/KIAA1542, located closely to IRF7, and IRF7 rs1131665 (glutamine (Gln) 412 arginine (Arg)) with systemic lupus erythematosus (SLE), causal variants have not been established. In this study, we resequenced exons and introns of IRF7 to screen for all common polymorphisms, and examined whether they were associated with SLE in 416 Japanese patients with SLE and 505 healthy controls. We also tested whether the association of PHRF1 rs4963128 with SLE was replicated in a Japanese population. None of the IRF7 polymorphisms was associated with SLE. PHRF1 rs4963128T was not significantly associated with occurrence of SLE either; however, this allele was significantly increased in SLE with anti-Sm antibodies (6.8%) as compared with healthy controls (3.1%, P = 0.014, odds ratio [OR] 2.31) and SLE without anti-Sm antibodies (3.3%, P =0.041, OR 2.12). This allele was also increased in SLE with renal disorder (5.1%) as compared with those without renal disorder (2.4%, P = 0.047, OR 2.17). These results confirmed recently reported association of PHRF1 rs4963128T with anti-Sm antibody positive SLE in African-American populations, and supported the role of PHRF1-IRF7 region in the genetics of SLE. [ABSTRACT FROM AUTHOR]