In 2003, an RA-associated PAD4 haplotype consisting of 4 exonic single nucleotide polymorphisms (SNPs) was identified24, and the increase in PAD4 protein levels in the synovium of RA patients compared to healthy individuals is due to the increased stability of the PAD4 mRNA containing these SNPs. The gene discussed is PADI4; the disease is rheumatoid arthritis.