The higher baseline serum levels observed in marathon runners, in osteoarthritis, and rheumatoid arthritis than in healthy controls (Neidhart et al., 2000; Garnero et al., 2001; Sharif et al., 2007) and the larger lag time to return to basal levels after a marathon (Neidhart et al., 2000; Kim et al., 2009) than after a moderate physical activity (Mündermann et al., 2005) suggest a maintained increase in synthesis or diffusion due to the rapid elimination of COMP once it has reached the circulation (Andersson et al., 2006). This evidence concerns the gene COMP and rheumatoid arthritis.