![]() ![]() Additionally, somatic mosaicism may contribute to the clinical variability of these conditions. In contrast, in-frame mutations yield shorter but otherwise normal subunits that interfere with production of mature collagen by preventing incorporation of subunits into triple helices, producing the more severe collagenopathies. If a normal second COL2A1 gene were present, normal procollagen production could still continue, although at a slower rate. For example, relatively mild Stickler's syndrome phenotypes can result from production of shortened polypeptide chains without a terminal carboxy unit, making the mutation equivalent to a stop codon. In general, for type II collagen, mutations that yield an abnormal but partially functioning procollagen subunit are associated with far more severe clinical disease than mutations that completely prevent expression of one of the two alleles of collagen genes. Alteration of any of the biosynthetic pathways results in abnormal collagen. All collagens are produced by biochemical pathways that involve numerous posttranslational events before assembly of mature collagen. The family of collagens represents a series of highly vulnerable gene-protein systems. Since then, the molecular genetics and biosynthesis of collagen production have been elucidated. The diverse tissues affected in these conditions have as primary constituents a large proportion of type II collagen, and Maumenee suspected that alterations of collagen protein caused Stickler's syndrome and other diseases. In 1979, Maumenee proposed that diseases such as Stickler's syndrome could be explained in terms of metabolic errors in collagen production and processing. Collagens II, IX, and XI have the highest concentrations in ocular tissues, and diseases affecting these proteins may be nosologically organized according to the aberrant collagen. At least 15 types of collagen are present in the body, each having its own tissue distribution, biochemical structure, and physical properties. Collagen is the most ubiquitous constituent molecule in connective tissue. One commonality shared by these disorders is abnormal collagen production or processing. These conditions display tremendous phenotypic variability and affect numerous different tissues, often making classification and diagnosis difficult for the clinician. Among these diseases are Stickler's syndrome, Marshall's syndrome, Kniest's syndrome, spondyloepiphyseal dysplasia congenita, achondrogenesis, hypochondroplasia, Wagner's disease, and erosive vitreoretinopathy, and snowflake vitreoretinal degeneration. These include lattice retinal degeneration, pathologic myopia, retinitis pigmentosa, and familial exudative vitreoretinopathy.Ī broad class of diseases known as connective tissue diseases manifests diverse vitreous and variable skeletal abnormalities. Several other conditions that involve the retina and vitreous and may be influenced by genetics are discussed elsewhere in this treatise. As molecular genetics improves, progress in understanding not only pathogenesis but also classification will occur. There has been some confusion in the clinical classification of the vitreoretinal dystrophies. ![]() Some of these conditions are clinically distinct and recognizable, whereas others represent a continuum of clinical disease. This chapter discusses heredofamilial vitreoretinal dystrophies including Stickler's syndrome, Marshall's syndrome, Kniest's syndrome, spondyloepiphyseal dysplasia congenita, achondrogenesis, hypochondroplasia, Wagner's disease, erosive vitreoretinopathy, snowflake vitreoretinal degeneration, juvenile hereditary retinoschisis, Goldmann-Favre tapetoretinal dystrophy, enhanced S-cone syndrome, and autosomal dominant vitreoretinochoroidopathy. Heredofamilial vitreoretinal dystrophies affect the vitreous body and the retina, comprising a heterogeneous group of diseases. ![]() Albert & Jakobiec's Principles & Practice of Ophthalmology, 3rd Edition CHAPTER 189 - Heredofamilial Vitreoretinopathies
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