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Canine Mendelian disease record

X-Linked Progressive Retinal Atrophy 2 (XLPRA2; Type A PRA)

X-Linked Progressive Retinal Atrophy 2 (XLPRA2; Type A PRA). X-linked recessive. Observed in 0 of 266 breeds tested in the Sniff Atlas, with measured variant frequencies drawn from 242,662 dogs (Donner 2023). Whether a dog carrying this variant is at risk depends on the disease’s inheritance pattern; outcome also depends on penetrance, modifiers, and environment. The frequencies below describe variant prevalence, not confirmed disease incidence.

OMIA identifier
OMIA:001518-9615
X-linked recessive
Source dataset
Sniff Atlas v1.0.1 / DOI
The human connection

A model of human macular degeneration, X-linked atrophic

This canine condition is studied as a natural model of macular degeneration, X-linked atrophic in people; it is not the same as a human macular degeneration, X-linked atrophic diagnosis. Studying dogs can move medicine forward for everyone; the canine disease remains the subject.

MONDO:0010443 OMIM 300029OMIM 300455

Mapped from OMIA via the human disease's OMIM entry to the Mondo Disease Ontology (Monarch Initiative, CC-BY 4.0). Closely related human conditions exist for this gene. Sniff renders this as a model-of link; the canine disease remains the subject of this page.

About this disease

From OMIA's curated record

Documented in OMIA (Online Mendelian Inheritance in Animals). This describes the disease as recorded in the published literature, not a prediction for any individual dog. As of 2026-08-27.

Summary

The difference between XLPRA1 (OMIA:000831-9615) and XLPRA2 (this entry) 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."

Clinical features

Beltran et al. (2006): "Abnormal development of photoreceptors was recognizable as early as 3.9 weeks of age. Outer segment (OS) misalignment was followed by their disorganization and fragmentation. Reduction in length and broadening of rod and cone inner segments (IS) was next observed, followed by the focal loss of rod and cone IS at later time points. The proportion of dying photoreceptors peaked at approximately 6 to 7 weeks of age and was significantly reduced after 12 weeks. In addition to rod and cone opsin mislocalization, there was early rod neurite sprouting, retraction of rod bipolar cell dendrites, and increased Müller cell reactivity. Later in the course of the disease, changes were also noted in horizontal cells and amacrine cells." As summarised by these authors: "XLPRA2 is an early-onset model of XLRP that is morphologically characterized by abnormal photoreceptor maturation followed by progressive rod-cone degeneration and early inner retina remodeling. "

Molecular genetics

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 "a two-nucleotide deletion (delGA) in 1084–1085" in the canine RPGR gene as a causal mutation for a form of X-linked PRA they call XPRA2. The authors noted that this deletion "results in a frameshift that significantly changes the deduced peptide sequence, causing an increased isoelectric point (4.30 versus 4.01), and leads to the inclusion of 34 additional basic residues before prematurely terminating translation 71 amino acids downstream".

Human analog

OMIA links this condition to its human counterpart in OMIM (Mendelian Inheritance in Man), the place to read across to the deeper human literature for the same biology.

Disease · OMIM 300029 Disease · OMIM 300455 Disease · OMIM 300834 Disease · OMIM 304020 Gene · OMIM 312610

Source: OMIA (Nicholas, Tammen & the Sydney Informatics Hub), entry OMIA:001518-9615, doi:10.25910/2AMR-PV70 (CC-BY 4.0).

OMIA curates the disease definition, the clinical description and the reference list. The cross-species disease identity is Monarch's. Sniff renders these and adds the breed-level frequencies, the plain-language summary, and a stated reason wherever a number is missing.

The evidence

Published references

The peer-reviewed papers behind this disease, curated by OMIA. Starred entries are OMIA-designated landmark papers. Showing 6 of 27.

References curated by OMIA (Nicholas, Tammen & the Sydney Informatics Hub), doi:10.25910/2AMR-PV70 (CC-BY 4.0). Full list at the OMIA entry.

Your breed

See what X-Linked Progressive Retinal Atrophy 2 (XLPRA2; Type A PRA) looks like in your dog's breed.
Variant frequency by breed

Observed only in small-sample breeds

Maximum variant frequency per breed across variants in the Donner 2023 cohort, with . The list below is split into well-sampled breeds (n ≥ 50 tested) and small-sample breeds (n < 50, where the Wilson CI typically spans more than 20 percentage points and frequencies should not be compared directly to the well-sampled entries). Frequencies are population-level, not per-litter or per-line.

Scope of this record

Scope

This record carries the breed-level carrier frequencies from the Donner 2023 cohort. Penetrance data (the fraction of at-risk dogs that develop the phenotype) is not yet quantified for this disease in the Sniff Atlas v1.0.1. The OMIA entry is the authoritative reference for the clinical phenotype, inheritance pattern, and gene assignment.

Predicted disease relevance at the per-dog level is UNPROVEN. The variant frequency is measured; phenotype outcome depends on penetrance, environment, and modifier loci. Consult a veterinarian for clinical interpretation.

How to cite this record

Citations

If you use this record in published work, cite the Sniff Atlas (the published dataset that carries the breed-level carrier frequencies) and the upstream sources:

  • Sniff Atlas v1.0.1 for the per-breed carrier frequencies:

    Gehring, M. (2026). Sniff Atlas v1.0.1. Zenodo. https://doi.org/10.5281/zenodo.20566358. CC-BY 4.0.

  • OMIA for the disease definition, inheritance, and gene assignment:

    Nicholas, F. W., & Tammen, I. (2024). OMIA. Sydney Informatics Hub, The University of Sydney. https://doi.org/10.25910/2AMR-PV70. Entry: OMIA:001518-9615.

  • Donner et al. 2023 for the breed × variant carrier-frequency cohort:

    Donner, J., Freyer, J., Davison, S., Anderson, H., Blades, M., Honkanen, L., et al. (2023). Genetic prevalence and clinical relevance of canine Mendelian disease variants in over one million dogs. PLOS Genetics, 19(2), e1010651. https://doi.org/10.1371/journal.pgen.1010651.

Full citation formats (BibTeX, RIS, CITATION.cff) at sniff.world/cite.

Related

Related

Last updated
Sources: Sniff Atlas v1.0.1 · OMIA OMIA:001518-9615 · Donner et al. 2023