COMP is a non-collagenous glycoprotein and is belongs to the thrombospondin family of extracellular proteins. COMP is a calcium-binding protein of high molecular weight （>500kDa） found in the extracellular matrix of articular， nasal and tracheal cartilage. COMP is not only cartilage-derived but is common in other tissues， such as synovium and tendon. Intact COMP is pentameric， with five equal subunits and the carboxy-terminal globular domain of native COMP binds to collagens I， II， and IX. COMP molecules are vital for conserving the properties and integrity of collagen network. Moreover COMP has a storage and delivery function for hydrophobic cellsignaling molecules such as vitamin D. Mutations of the COMP gene cause Pseudoachondroplasia and some forms of multiple epiphyseal dysplasia which implicates that it is vital that COMP develops and functions normally. It is a well-known fact that serum levels of COMP offer essential data about metabolic changes taking place in the cartil
