Stickler syndrome and vitreoretinal degeneration: correlation between locus mutation and vitreous phenotype. Apropos of a case.

BACKGROUND: Autosomal dominant vitreoretinopathies are characterized by genetic heterogeneity. Structural mutations in COL2A1 are the most frequent cause of Stickler syndrome with ocular involvement. The affected patients have a characteristic vitreous alteration, so-called membranous vitreous, or type 1 vitreous phenotype. Recently a novel mutation in the gene encoding the alpha 1 chain of type XI collagen (COL11A1) was reported in rare Stickler pedigrees, with a different, so-called beaded or type 2 vitreous phenotype.
METHODS: Five patients of an Italian family affected by high myopia, high frequency of retinal detachment, and other systemic stigmata evocative of Stickler syndrome (flat midface, depressed nasal bridge, short nose, spondyloepiphyseal dysplasia and osteoarthritis) were studied. Genetic investigations were also performed, considering three candidate loci for Stickler syndrome and Wagner syndrome (COL2A1, COL11A1, WGN1).
RESULTS: Segregation analysis was performed utilizing polymorphic markers. COL2A1 and WGN1 segregations were excluded; COL11A1 showed concordance with the disease. The vitreous phenotype of the family was a typical type 1 or "membranous" vitreous, although all the previously reported COL11A1-related Stickler syndromes had always shown the type 2 or "beaded" vitreous phenotype.
CONCLUSIONS: The clear presence of the type 1 or "membranous" vitreous phenotype in our family, despite the probable mutation in the COL11A1 gene, suggests greater phenotypical heterogeneity and a more extensive mutation spectrum, even of the COL11A1 gene, than previously thought, explaining the basis for the different vitreous phenotypes seen in Stickler syndrome.