 Mutations are in the exons encoding the type III repeats (exons 8–14) and C-terminal domain (exons 15–19).The most common mutations in COL9A1 are in exons 8-10, in COL9A2 in exons 2-4, and in COL9A3 in exons 2-4.Altogether, those mutations cover 10% of the patients.