Categories: Vision / eye phene

Links to possible relevant human trait(s) and/or gene(s) in OMIM: 300029 (trait) , 312610 (gene) , 304020 (trait) , 300834 (trait) , 300455 (trait)

Mendelian trait/disorder: yes

Mode of inheritance: X-linked

Disease-related: yes

Key variant known: yes

Year key variant first reported: 2002

Cross-species summary: This disorder has been renamed in OMIA on the basis of the review by Miyadera et al. (2012)

Species-specific symbol: XLPRA1

Species-specific description: The difference between XLPRA1 (this entry) and XLPRA2 (OMIA 001518-9615) is summarised by Appelbaum et al. (2020) as "XLPRA1-affected dogs have normal PR morphogenesis, after which progressive rod–cone degeneration develops in the peripheral retina, gradually advancing toward the optic disc. . . . The phenotype associated with XLPRA2 is very severe and manifests during early retinal development."

Molecular basis: Based on a comparative positional cloning approach (the canine disorder maps to a location on the canine X chromosome that is homologous with the location of the same disorder (RP3) in humans, which is due to mutations in the RPGR gene), Zhang et al. (2002) identified a "five-nucleotide deletion (delGAGAA) between 1028 and 1032" in the canine RPGR gene as a causal mutation for a form of X-linked PRA they call XPRA1. The authors also noted that "The XLPRA1 mutation causes a frameshift and immediate premature stop; the truncated protein is missing 230 C-terminal amino acids, causing a slight decrease in the isoelectric point (3.89 versus 4.01 in normal). By mutation scanning, we also found the same five-nucleotide deletion in the Samoyed breed with a clinically similar X-linked retinal degeneration (data not shown)" Kropatsch et al. (2016): "Whole exome sequencing in two PRA-affected Weimaraner dogs identified a large deletion [maximum size 5,006 bp] comprising the first four exons of the X-linked retinitis pigmentosa GTPase regulator (RPGR) gene".

Pathology: As summarised by Zeiss et al. (1999): " The earliest lesion detectable by electron microscopy was vesiculation of rod discs, followed by disruption of outer segments and death of rods. Loss of cones and progressive atrophy of inner retinal layers followed. Lesions were most severe in the peripheral retina and advanced toward the optic disc with disease progression. Significant variation in disease severity was present in males despite the presence of the same disease allele in all affected dogs." As concluded by the same authors: "X-linked retinal degeneration is characterized by initial degeneration of rod photoreceptors, followed by loss of cones and progressive atrophy of the inner retina. Carrier females display a phenotype consistent with random X-chromosome inactivation. Variation in genetic background may alter expression of the disease allele in affected animals, thus accounting for variation in phenotypic expression of the disease."

Breeds: Samoyed (Dog) (VBO_0201174), Siberian Husky (Dog) (VBO_0201233), Weimaraner (Dog) (VBO_0201401).
Breeds in which the phene has been documented. (If a likely causal variant has been documented for the phene, see the variant table breeds in which the variant has been reported).

Associated gene: