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VA Pakalnis, RC Tripathi, D Yee, KV Chalam; Histopathologic and Ultrastructural Characterization of Anterior and Posterior Capsule in Kniest Dysplasia . Invest. Ophthalmol. Vis. Sci. 2002;43(13):487.
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Purpose: To better define the pathogenic mechanism causing the lens-related ocular findings responsible for the formation of cataracts and dislocated lenses in Kniest Dysplasia, an autosomal-dominant spondyloepiphyseal dysplasia (SED) . Methods: The anterior and posterior capsule from a 4 year old girl diagnosed with Kniest Dysplasia (Metatrophic Dwarfism, Type II, OMIM 156550, caused by a mutation in Type II collagen, proalpha 1(II)-chain) with a dense white cataract (cataracta complicata) were removed through the pars plana using a vitrectomy technique performed for repair of a retinal detachment and processed routinely for transmission electron microscopy (TEM). Thick sections stained with toluidine blue were also obtained. Results: Ultrastructural analysis demonstrated marked epithelial metaplasia and fibrous tissue formation in the anterior subcapsular region. Epithelial cells formed into spindle-shaped fibroblast-like cells in the anterior capsule where electron dense granules were also noted.. There was thickening of both anterior and posterior capsules. The fibroblast-like cells appeared to be responsible for the production of regular collagen as well as basement-membrane material. Posterior proliferation of lens epithelium was noted in the posterior capsule. Dense, fine fibrobrillogranular material was also noted. Conclusion: Peculiar capsular and epithelial changes with aberrant formation of collagenous fibrous tissue was found in the cataractous lens of a child with Kniest Dysplasia. TEM and histopathologic analysis supports the theory that the underlying defect causing cataracts in this variant of SED is a collagen-synthesis defect and that mucopolysacharidosis plays little, if any, role in the pathogenesis of the cataractous ocular defect . In addition, there is a great similarity to the histopathological features of the cataracta complicata described in Lowe«s syndrome.
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