In a recent paper comparing marker proteins in serum and synovial fluid in patients with advanced osteoarthrosis (OA) and RA deduced that the only marker protein that revealed distinct higher levels in the serum than in the synovial fluid was matrix metalloproteinase-13, but further investigations may provide more information about the value of matrix metalloproteinase-13 as a potential marker to monitor the course of RA and OA (Andereya et al. 2006). The gene discussed is MMP13; the disease is rheumatoid arthritis.