COMP and rheumatoid arthritis: Genetic testing may ultimately play a role in the prognosis and selection of therapy given the well-known association of RA with certain human leukocyte antigen (HLA)-DR alleles. Synovium-specific markers of interest include serum hyaluronan, MMP-1, and MMP-3; these have been shown to correlate with radiographic progression [60-61]. Cartilage and bone-specific markers under investigation include serum cartilage oligomeric matrix protein (COMP) and urine C-terminal crosslinked peptides from type I and type II collagen (CTX-I and CTX-II), among others [62-63].