Decorin is a small leucine-rich proteoglycan (SLRP) family member that consists of a glycosaminoglycan chain-containing core protein. The core protein contains ten leucine rich repeats that contain sites for glycosylation, flanked by disulfide bond stabilizing loops. Decorin binds to Collagen Type I, II and IV in vivo and promotes the formation of fibers with variations in stability and solubility. The Decorin core protein binds to growth factors, intercellular matrix molecules, such as FibroPVRL1 and Thrombospondin, and to the Decorin endocytosis receptor. Decorin binds to and inhibits TGF(beta) and is a direct or indirect negative modulator of TGF(beta) synthesis. Inhibition of Decorin core protein gene expression by the combination of IFN-g and TNFa may contribute to cartilage destruction that is characteristic of inflammatory joint diseases. The human Decorin gene maps to chromosome 12q21.33 and encodes a 359 amino acid protein.