PADI4 and rheumatoid arthritis: The three nonsynonymous SNPs (padi4_89, padi4_90 and padi4_92) in PADI4 were fully correlated (r2 = 1.00) with each other in controls and RA patients, and constitute only two common haplotypes, ACC and GTG (with letters representing the nucleotides found at padi4_89, padi4_90, and padi4_92, respectively) in all subjects except only for three.