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F. L. Munier, L. Chachoua, N. Haouari, O. Beltaief, S. Uffer, D. F. Schorderet; Honey Droplet and Gelatinous Drop-Like Corneal Dystrophies Are Allelic. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1001.
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Honey Droplet Corneal Dystrophy is a rare corneal dystrophy (HDCD), also named familial band-shaped spheroidal keratopathy. This autosomal recessive condition is characterized by band-shaped golden-colored nodules with oily appearance at slit lamp examination, corresponding to subepithelial amorphous globular deposits with positive staining for elastic tissue in light microscopy. A close association between gelatinous drop-like corneal dystrophy and band-shaped spheroidal corneal degeneration has been suggested. We ascertain two families with HDCD in order to identify the underlying gene defect.
22 individuals from 2 consanguineous families originating from Algeria (family A) and Tunisia (family B) underwent ophthalmologic examination. Light microscopy (LM) was performed in 5 of the 6 affected patients and transmission electron microscopy (TEM) in one of them. Blood samples were collected from 21 family members including the 6 affected individuals. Homozygositzy mapping was performed with 650 microsatellites mapping covering the whole genome (ABI mapping set 2.5). Bidirectional sequencing of the M1S1 gene was performed using the Big Dye Terminator version 1.
LM revealed the presence of massive subepithelial and anterior stromal amyloid material (Congo Red positive) mixed with spheroidal-type deposits in family A. In contrast, massive subepithelial and anterior stromal spheroidal-type material was associated with underlying fusiform deposits (Congo Red positive) throughout the rest of the stroma in family B. TEM confirmed the amorphous and fibrillar nature of the spheroidal and amyloid material respectively. D1S2873 was homozygous in all affected individuals and heterozygous in the parents and in 8 non-affected individuals. This marker is in close proximity to M1S1 (TACSTD2), a gene implicated in GDCD. Sequencing of this gene identified a novel C119S mutation in family A, and a Y224X mutation in family B.
Mutations in M1S1 cause two distinct clinical and histopathologic phenotypes, namely GDCD and HDCD, leading to the deposition of amyloid and combined amyloid plus spheroidal material respectively. The composition and pathogenesis of spheroidal deposition remain to be elucidated.
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