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Michael B Powner, Mark C Gillies, Meidong Zhu, Paul S Bernstein, Gregory S Hageman, Catherine A Egan, Marcus Fruttiger; Pan-retinal, subretinal aggregates in Macular Telangiectasia Type 2. Invest. Ophthalmol. Vis. Sci. 2014;55(13):6320.
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Macular Telangiectasia Type 2 (MacTel type 2) is known to affect a specific region in the macula. It is characterised by Muller cell, macular pigment and photoreceptor loss and vascular tortuosity. So far no clinical phenotypes have been described outside this central region. Here we used histopathology to assess whether there are any sub-clinical abnormalities in the peripheral retina in MacTel type 2.
Post mortem tissue from three MacTel type 2 donors was investigated. Paraformaldehyde tissue was sectioned and immunohistochemistry undertaken looking for photoreceptor, retinal pigment epithelium and glia markers. For ultra-structural analysis paraformaldehyde/glutaraldehyde fixed tissue was osmium tetroxide treated and processed. Semi thin sections were stained with toluidine blue and ultrathin sections were stained with lead citrate for electron microscopy.
Subretinal debris aggregates were found in all three cases of MacTel type 2. In two cases they were found close to the optic nerve head, in the third they were found pan retinal. These debris aggregates included photoreceptor outer segments, containing opsins but not the mitochondrial marker COX2 (inner segment marker). The aggregates also expressed MERTK (but not Stra6 or RPE65) and CRALBP, which co-localised with pigment granules. Localised expression of Vimentin and GFAP was also seen. There was no evidence of increased inflammatory cells in the subretinal space. Semi thin sections reveal subretinal debris aggregates packed with outer segment fragments, but also a pan retinal thin layer of extracellular debris covering the apical surface of the RPE. The RPE have restricted microvilli but otherwise appear healthy. The thin debris layer contains degenerating outer segments and membranous structures.
The clinical phenotype of MacTel type 2 has been well characterised, and to date all evidence suggests a pathology restricted to a specific region in the macula. Our data shows a sub clinical phenotype associated with MacTel type 2 that is pan retinal in the subretinal space. We have not seen any such structures in age matched control tissues.
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