Type XXI collagen

Type XXI collagen belongs to the family of fibril-associated collagens with interrupted triple helices and serves as a molecular bridge between collagen fibrils and other extracellular matrix proteins. Type XXI collagen is expressed in heart, placenta, stomach, jejunum, skeletal muscle, kidney, lung, pancreas, and lymph nodes. Missense mutations in humans are associated with blood pressure, and copy-number variations are associated with cleft lip/palate. There is no mouse ortholog of COL21A1, so null mice have not been reported. The biological function of type XXI collagen requires elucidation; however, data suggest that type XXI collagen may play a role in blood vessel assembly, muscle cell differentiation, and fibroblast activity. Gene expression is deregulated in cancer and muscle disorders, and autoantibodies against type XXI collagen can be found in sera of patients with skin disorders. Biomarkers need to be developed to determine the relevance of type XXI collagen under pathological conditions.