In agreement with our results, IHC analysis of human synovial tissue specimens revealed that the PPM1A protein expression was much lower in synovial tissue derived from patients with OA than that in people with RA or ankylosing spondylitis (AS) (46), indicating a dispensable role of PPM1A for synovial inflammation in OA. The gene discussed is PPM1A; the disease is ankylosing spondylitis.