retinitis pigmentosum

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A pathological condition where the retina, when viewed through an ophthalmoscope, is seen dotted with jet-black pigment spicules. These represent dying photoreceptor cells. There are at least seven autosomal dominant, one autosomal recessive, and three X-linked recessive forms of the disease. One mutant autosomal gene for RP maps at the site (on 3p) of the gene that encodes rhodopsin (q.v.). Another gene (at 6p) encodes a glycoprotein called peripherin. This is an adhesion molecule localized in the rim of each disc. It joins adjacent discs and maintains their integrity as they lie stacked together in the outer segment of the photoreceptor cells. The most common RP mutation in American patients is P23H, a missense mutation in the rhodopsin gene. The mutated rhodopsin forms high molecular weight aggregates which impair the ubiquitin-proteasome pathway (q.v.) of protein degradation. See contiguous gene syndrome, retina, rhabdomere.

Subjects: Genetics and Genomics.

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