COL9A1 and Stickler syndrome: Autosomal dominant Stickler syndrome can be caused by mutations in the COL2A1, COL11A1 or COL11A2 genes, and an autosomal recessive form is caused by mutations in the COL9A1 gene.2,3 Patients with mutations in the COL2A1 gene have a characteristic ‘membranous’ or type I vitreous phenotype, and they account for more than 80% of the patients with Stickler syndrome.4 Patients with COL11A1 mutations have a ‘beaded’ or type 2 vitreous phenotype, and patients with COL11A2 mutations lack any ocular alterations.1