PADI4 and rheumatoid arthritis: In view of the fact that we found an association of the GTG haplotype with the risk for RA and higher gene expression in carriers of these haplotypes, it was also of interest to evaluate the activity of PAD4 in leukocytes to determine the effect of these variants on the activity of the PAD4 enzyme; we observed higher PAD4 activity in patients carrying the GTG haplotype.