- A mutation in the gene encoding the alpha 2 chain of the fibril-associated collagen IX, COL9A2, causes multiple epiphyseal dysplasia (EDM2). Muragaki, Y., Mariman, E.C., van Beersum, S.E., Perälä, M., van Mourik, J.B., Warman, M.L., Olsen, B.R., Hamel, B.C. Nat. Genet. (1996)