Such features of alternative splicing explain the variability of phenotypes associated with COL2A1 mutations: mutations in a tissue-specific alternatively spliced exon of COL2A1 may result in Wagner’s disease or ocular only Stickler syndrome whilst Stickler syndrome due to mutations of COL2A1 without involving exon 2 affects both cartilage and vitreous. The gene discussed is COL2A1; the disease is Stickler syndrome.