PADI4 and rheumatoid arthritis: The fourth, synonymous SNP (padi4_104) in PADI4 was also associated with RA susceptibility (OR 1.33, 95% CI 1.18 to 1.50), but this allelic association was not statistically independent from the above haplotype association because this SNP was very highly correlated (r2 = 0.78 approximately 0.79) with the nonsynonymous SNPs.