Retinitis Pigmentosa 78

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2019-09-22
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A number sign (#) is used with this entry because of evidence that retinitis pigmentosa-78 (RP78) is caused by homozygous or compound heterozygous mutation in the ARHGEF18 gene (616432) on chromosome 19p13.

For a general phenotypic description and a discussion of genetic heterogeneity of retinitis pigmentosa, see 268000.

Clinical Features

Arno et al. (2017) studied 3 unrelated individuals with simplex retinitis pigmentosa. All presented in their third to fourth decades with central visual disturbance, visual field defects, and mild nyctalopia. Examination at ages 37, 38, and 51 years, respectively, revealed visual acuities ranging from 20/30 to 20/1250, with the worst in the oldest individual (patient 2; GC3626). Fundus examination showed optic disc pallor, attenuated retinal vessels, and irregular mid-peripheral intraretinal pigment migration. Fundus autofluorescence (FAF) imaging revealed widespread irregular peripheral hypo-autofluorescence. Optical coherence tomography (OCT) demonstrated intraretinal cysts in all 3 patients, and in patient 2 the inner-segment ellipsoid line (ISe) was preserved only in the foveal region, indicating a greater degree of retinal degeneration. Full-field electroretinography (ERG) at ages 29 to 30 years demonstrated severe generalized retinal dysfunction, affecting rod more than cone photoreceptors. The pattern ERG was subnormal in patients 1 (GC18203) and 3 (GC17880), indicating relatively mild macular involvement, but was undetectable in individual 2, consistent with severe macular involvement. There was no clinical evidence of other systemic, neurologic, or epithelial disease in any of the individuals.

Molecular Genetics

In a total of 829 individuals diagnosed with inherited retinal disease, Arno et al. (2017) performed whole-exome or whole-genome sequencing and identified homozygous or compound heterozygous mutations in the ARHGEF18 gene (616432.0001-616432.0005) in 3 unrelated patients with simplex RP. The mutations segregated with disease in the 2 families for which relatives' DNA was available. Four of the mutations were not found in the ExAC database and the other 1 was not found in the Exome Sequencing Project database. The authors noted that certain features in these patients resembled those seen in CRB1 (604210) retinopathy (see RP12, 600105), including irregular autofluorescence, peripheral nummular pigmentation, and retinal thickness; however, all 3 patients were negative for mutation in the CRB1 gene. Direct Sanger sequencing of ARHGEF18 in 10 additional patients with a similar retinal phenotype did not reveal any mutations.