COMP and multiple epiphyseal dysplasia: Notably, PSACH is caused exclusively by mutations in COMP, whereas autosomal-dominant forms of MED can also be caused by mutations in matrilin-3 (MATN3) and type IX collagen (COL9A1, COL9A2, COL9A3) [13,14,15,16,17], other constituents of the cartilage ECM that have all been shown to interact directly with COMP [5,7,18].