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Stickler Syndrome, Type I
High myopia and vitreous degeneration dominate the ocular manifestations of Stickler syndrome, type I. The vitreous often appears optically empty as it liquefies and the fibrils degenerate. The vitreous is sometimes seen to form ‘veils’, especially in the retrolenticular region but they may also float throughout the posterior chamber. They are often attached to areas of lattice degeneration in the retina as well as other areas. Posterior vitreous detachments are common. Vitreoretinal degeneration is progressive and by the second decade rhegmatogenous detachments occur in half of affected patients. As many as three quarters of adult patients have retinal breaks. The retina has pigmentary changes with deposition circumferentially near the equator and more peripherally. Hypopigmentation is more common early creating a tessellated appearance. Lenticular opacities occur also early with cortical flecks and wedge-shaped changes.
The ERG may be normal early but evidence of rod and cone dysfunction soon appears and is progressive. Dark adaptation is defective later in the course of the disease. The EOG is virtually always depressed. The visual field is constricted and may show a ring scotoma coincident with the equatorial chorioretinal atrophy.
It has been suggested that there is a nonsyndromic or ocular type of Stickler syndrome lacking many of the extraocular features characteristic of the complete syndrome. However, the evidence for the ocular type described here as a distinct entity remains slim and the clinical picture may simply reflect variable expressivity of mutations in the same gene. Type I Stickler syndrome has multiple systemic features such as cleft palate, hearing impairment, premature arthritis, micrognathia, kyphoscoliosis, and some signs such as arachnodactyly that are found in the Marfan syndrome.
This is an autosomal dominant disease of collagen formation as a result of mutations in the COL2A1 gene (12q13.11-q13.2). The mutations causing both syndromal and the suggested nonsyndromal ocular type of Stickler disease are in the same gene. Mutations in the same gene are known to cause autosomal dominant rhegmatogenous retinal detachments in patients who have none of the systemic clinical signs (609508). These patients may lack the signs of vitreous degeneration seen in Kniest dysplasia (156550) and in the disorder described here.
There is better evidence for a second type of Stickler syndrome, STL2 or type II (604841) based on phenotypic differences and the fact that a second locus (1p21) containing mutations in COL11A1 has been linked to it.
Type III is caused by mutations in COL11A2 and has systemic features similar to types I and II but lacks the eye findings since this gene is not expressed in the eye.
The combination of progressive vitreoretinal degeneration, frequency of posterior vitreous detachments, and axial myopia creates a lifelong threat of retinal tears and detachments. Half to three quarters of all patients develop retinal tears and detachments. Certainly all patients with Stickler syndrome deserve repeated and thorough retinal exams throughout their lives. In addition to prompt treatment of tears and detachments, some have advocated prophylactic scleral banding to reduce vitreous traction, or applying 360 degree cryotherapy.