Together with PADI4 [41], the protein level of PADI2 was reported to be highly increased in RA synovial tissues compared with that in samples from patients with osteoarthritis and ankylosing spondylitis, and some SNPs of the PADI2 gene were shown to be significantly associated with the presence of RA [42]. This evidence concerns the gene PADI4 and ankylosing spondylitis.