Retinitis Pigmentosa 6

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2019-09-22
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For a phenotypic description and a discussion of genetic heterogeneity of retinitis pigmentosa, see 268000.

Mapping

Two separate loci for X-linked recessive retinitis pigmentosa have been mapped to the short arm of the X chromosome, RP2 at Xp11.4-p11.23 (312600) and RP3 at Xp21.1 (300029). On the basis of different linkage relationships, it has been suggested that there is a third RP locus on Xp, designated RP6 and thought to be located at Xp21.3-p21.2. Ott et al. (1990) performed a multilocus linkage analysis of 62 family pedigrees with X-linked RP. In 60 to 75% of the families, location of an XLRP gene was estimated at 1 cM distal to OTC, and in 25 to 40% of the families, an XLRP locus was located halfway between DXS14 (p58-1) and DXZ1 (Xcen), with an estimated recombination fraction of 25% between the 2 XLRP loci. Ott et al. (1990) considered that there was good evidence also for a third XLRP locus, midway between DXS28 (C7) and DXS164 (pERT87), supported by a likelihood ratio of 293:1 for 3 versus 2 loci.

Clinical Management

Grover et al. (2000) evaluated the progression of visual impairment in carriers of X-linked recessive retinitis pigmentosa (XLRP). They described the relationship between retinal findings at presentation and the extent of subsequent deterioration. They followed visual acuity, visual field, and electroretinograms in 27 carriers of XLRP and described 4 grades of fundus findings from grade 0 (normal) to grade 3 (diffuse changes). They found that carriers of XLRP with only a tapetal-like retinal reflex (grade 1) at presentation were more likely to retain visual function than those with peripheral retinal pigmentation. Grover et al. (2000) concluded that these data are useful in counseling such carriers as to their visual prognosis.