Accumulation of granular osmiophilic material in blood vessel walls. Osmiophilic material becomes black upon staining with osmium tetroxide. Deposition of granular osmiophilic material (GOM) is the vascular pathological hallmark of CADASIL, which is the most prevalent hereditary small vessel disease and is caused by missense mutations in the NOTCH3 gene. GOM have been shown to contain NOTCH3 ectodomain (NOTCH3ECD) and extracellular matrix proteins, and can be visualized ultrastructurally in the tunica media of small arteries and capillaries. These electron dense GOM deposits are located in the basement membrane of mural cells, i.e. vascular smooth muscle cells and pericytes. In both manifest and pre-manifest CADASIL patients, GOM deposits are present not only in brain vessels, but also in vessels of other organs, such as the skin. [from HPO]
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