COMP and Pseudoachondroplasia
- DOI:
- 10.1093/med/9780199934522.003.0200
Pseudoachondroplasia (PSACH) is a dominantly inherited form of short-limb short stature. Both mild and typical forms are recognized, comprising a spectrum of clinical severity. A definitive diagnosis can be made on the basis of radiographs showing delayed epiphyseal os- sification, epiphyseal and metaphyseal irregularities, and a characteristic anterior beaking of the vertebral bodies apparent on lateral projection. In addition to short stature, loose joints due to ligamentous laxity, joint pain, varus and/or valgus deformities at the knees and scolio- sis characterize the phenotype. The major complication is degenerative joint disease, particu- larly in the hips, which can lead to joint replacement in the third or fourth decade of life. Pa- tients with PSACH have defects in cartilage oligomeric matrix protein (COMP), a pentameric glycoprotein of the extracellular matrix. Most patients with typical PSACH studied to dat e have been shown to be heterozygous for structural mutations in the COMP gene, either mis- sense mutations or small deletions. The phenotype appears to primarily result from reduced secretion of COMP, the presence of abnormal COMP in the extracellular matrix, and disrupt- ed interactions between COMP and other matrix molecules.
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