Retinitis Pigmentosa 57

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2019-09-22
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A number sign (#) is used with this entry because retinitis pigmentosa-57 (RP57) is caused by homozygous mutation in the PDE6G gene (180073).

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

Clinical Features

Dvir et al. (2010) studied an extended Israeli Muslim Arab pedigree segregating severe early-onset autosomal recessive retinitis pigmentosa in which affected individuals had markedly constricted visual fields, ranging from 10% to less than 5%, with tiny residual islands of central vision. Nevertheless, best-corrected visual acuity was relatively good. Both scotopic and photopic electroretinograms were severely reduced or completely extinct as early as 4 years of age. Funduscopy showed typical bone spicule-type pigment deposits spread mainly at the midperiphery, as well as optic disc pallor. Macular involvement was indicated by the lack of foveal reflex and typical cystoid macular edema, confirmed by optical coherence tomography. Dvir et al. (2010) noted that these findings were similar to those reported in patients with RP due to mutations in the PDE6A (RP43; see 180071) and PDE6B genes (RP40; 613801).

Mapping

Dvir et al. (2010) performed genomewide homozygosity mapping in an extended Israeli Muslim Arab pedigree segregating autosomal recessive RP and identified only 1 region of shared homozygosity, a 5.2-Mb interval at the telomeric end of chromosome 17, between SNP rs10931 and the telomere at 17q25.3. A recombination event in an unaffected relative reduced the interval to 4.7 Mb between SNP rs868432 and the telomere, an interval containing 203 genes.

Molecular Genetics

In an extended Israeli Muslim Arab pedigree segregating autosomal recessive RP mapping to chromosome 17q25.3, Dvir et al. (2010) sequenced the candidate PDE6G gene and identified homozygosity for a splice site mutation in affected individuals (180073.0001); all unaffected family members were heterozygotes or carried 2 wildtype alleles. No carriers of the splice site mutation were found among 256 Muslim Israeli controls, including 135 Muslim Arabs from northern Israel, 70 Muslim Arabs from central Israel, and 51 Bedouins. However, the mutation was detected in heterozygosity in 7 (8.3%) of 84 randomly selected adults from the same village in which the RP57 family resides, indicating that it represents a founder mutation in that village.