Genetic and Environmental Association with Rheumatoid Arthritis

Abstract

Objectives. Smoking is associated with rheumatoid arthritis (RA) in individuals with the HLA-DRB1 shared epitope (SE). Anti-cyclic citrullinated peptide autoantibodies (ACPA) are the most specific serologic marker for RA. Genetic polymorphisms in a citrullinating (or deiminating) enzyme, peptidyl arginine deiminase type IV (PADI4) have been reproducibly associated with RA susceptibility in several populations. The SE alleles have been found to be predominantly associated with anti-cyclic citrullinated peptide antibodies (ACPA)-positive RA. These risk factors have not been identified for ACPA-negative RA. We investigated whether SE-containing HLA-DRB1 alleles, smoking, or the combination contribute to the development of RA depending on the presence or absence of serologic markers in a Korean population. We also investigated whether PADI4 polymorphisms contribute to ACPA-negative as well as -positive RA and whether they interact with HLA-DRB1 shared epitope (SE) alleles or smoking which have been associated with RA susceptibility. Methods. All RA patients (n =1482) and controls (n = 1119) were Korean. Four-digit HLA-DRB1 typing was performed by a conventional PCR-SBT method. All 2,317 unrelated Korean subjects including 1,313 RA patients and 1,004 unaffected controls were genotyped for three nonsynonymous (padi4_89, padi4_90, and padi4_92) and one synonymous (padi4_104) single-nucleotide polymorphisms (SNPs) in PADI4 and for HLA-DRB1. Information about smoking history was obtained through a questionnaire. RA patients were tested for ACPA and rheumatoid factor (RF). Results. The SE alleles had significant effects on ACPA and RF formation. The DRB1*0901 allele was associated with the presence of ACPA (OR 2.49) and RF (OR 2.09). SE alleles and smoking were associated with both ACPA-positive and ACPA-negative RA. The combination of smoking and double SE increased the risk for ACPA-positive RA 36.11-fold and ACPA-negative RA 12.29-fold, compared with the risk among nonsmokers not carrying SE alleles. Interactions between SE alleles and smoking were observed for both ACPA-positive and RF-positive RA, although associations of RF-positive RA could be consequences of underlying ACPA-status. A functional haplotype of the three fully correlated nonsynonymous SNPs in PADI4 was associated with susceptibility to not only ACPA-positive (OR 1.60) but also -negative RA (OR 1.81). Gene-gene interactions between the homozygous RA-risk PADI4 haplotype and SE alleles were significant in both ACPA-positive (AP 0.47) and -negative RA (AP 0.62). In contrast, no interaction was observed between smoking and PADI4 polymorphisms. Conclusions. We demonstrated that SE alleles and smoking are associated with RA susceptibility regardless of ACPA or RF status but show stronger effects in ACPA/RF-positive RA than ACPA/RF-negative RA. A haplotype of nonsynonymous SNPs in PADI4 contributes to development of RA regardless of ACPA status. The SE-smoking interactions were present in ACPA-positive and RF-positive RA. The homozygous PADI4 haplotype contribution is affected by gene-gene interactions with SE alleles.