LEP and rheumatoid arthritis: Argente et al found that leptin levels in female were significantly higher than male with the same age especially after the age of 12 because leptin expression decreased in male and rose in female after the age of 12.[21] Leptin levels in peripheral blood of OA and rheumatoid arthritis (RA) patients were higher than normal person.[22] A high aggregation phenomenon of leptin in synovial fluid of patients with RA was detected.