Qualitative or quantitative defects of collagen 6

Qualitative or quantitative defects of collagen 6 encompass a spectrum of inherited muscle disorders caused by mutations in the genes encoding collagen VI (COL6A1, COL6A2, and COL6A3). Collagen VI is a major structural component of the extracellular matrix surrounding muscle fibers, tendons, skin, and other connective tissues. When collagen VI is either reduced in quantity (quantitative defect) or structurally abnormal (qualitative defect), it leads to a range of clinical conditions collectively known as collagen VI-related myopathies. The most recognized conditions within this spectrum include Ullrich congenital muscular dystrophy (UCMD) at the severe end, Bethlem myopathy at the milder end, and an intermediate phenotype bridging the two. The primary body systems affected are the musculoskeletal and connective tissue systems. Key clinical features include progressive muscle weakness, joint contractures (particularly of the elbows, ankles, and fingers), and proximal joint hyperlaxity (especially of the wrists and fingers), which is a distinctive hallmark. Patients may also experience skin abnormalities such as soft, velvety skin, keloidal scarring, and follicular hyperkeratosis. In more severe forms such as UCMD, respiratory insufficiency can develop early and may require ventilatory support. Bethlem myopathy typically presents with a milder, slowly progressive course, though contractures and mild respiratory compromise can still occur over time. Currently, there is no curative treatment for collagen VI-related myopathies. Management is supportive and multidisciplinary, focusing on physical therapy to maintain mobility and manage contractures, respiratory monitoring and intervention when needed, and orthopedic management. Research into potential therapies, including approaches to enhance collagen VI production or correct underlying defects through gene therapy, is ongoing but remains largely experimental.

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