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Canine Mendelian disease record

Progressive Retinal Atrophy (Discovered in the Lhasa Apso; IMPG2-related PRA4)

Progressive Retinal Atrophy (Discovered in the Lhasa Apso; IMPG2-related PRA4). Autosomal recessive. Observed in 3 of 266 breeds tested in the Sniff Atlas, with measured carrier frequencies drawn from 242,651 dogs (Donner 2023). Per-dog phenotype outcome depends on penetrance, modifiers, and environment; the carrier frequencies below describe variant prevalence, not disease incidence.

OMIA identifier
OMIA:002289-9615
Autosomal recessive
Source dataset
Sniff Atlas v1.0.1 / DOI
The human connection

A model of human retinitis pigmentosa 56

This is the canine counterpart of retinitis pigmentosa 56 in people. That makes affected dogs a naturally-occurring model of the human disease, and it is part of why studying dogs moves medicine forward for everyone. It does not mean your dog has the human disease. It means the two share an underlying biology.

In people, the disease is described as: Any retinitis pigmentosa in which the cause of the disease is a mutation in the IMPG2 gene.

In humans it is also called: RP56, IMPG2 retinitis pigmentosa, retinitis pigmentosa caused by mutation in IMPG2, retinitis pigmentosa type 56.

MONDO:0013314 OMIM 613581OMIM 616152

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 2026-06-03.

Summary

Many different forms of progressive retinal atrophy (PRA) exist and more than 10 different genes have been identified so far in dogs to have likely causal variants for PRA. Please review OMIA for other variants. This OMIA entry will focus on PRA due the variants in the IMPG2 gene.

Clinical features

Clinical signs are consistent with a rod-cone degeneration in both eyes. Initially, there may be mild attenuation of retinal blood vessels, hyper-reflectivity of the tapetum, optic disc discolouration and night blindness. As the disease progresses, the blindness becomes moderate to severe with attenuation of retinal blood vessel; hyper-reflectivity of the tapetum, due to retinal thinning; and optic disc atrophy (Hitti-Malin et al., 2020). Of the 19 out of 21 dogs for whom an age at diagnosis is known, approximately 50% were diagnosed between the age of 5 and 8 years (Hitti-Malin et al., 2020). [IT thanks DVM student Andrew Barker, who provided the basis of this contribution in April 2022].

Molecular genetics

Hitti-Malin et al. (2020): "whole-genome sequencing analysis that revealed a long interspersed element-1 (LINE-1) insertion upstream of the IMPG2 gene."

Prevalence

Hitti-Malin et al. (2020): "validation of this variant [the LINE-1 variant] in 447 dogs of 123 breeds determined it was private to LA dogs. . . . The recently estimated mutant allele frequency of 0.1, generated from the 911 DNA tested LA during 2 years of use of a DNA test based on this work, indicates that 1 in 100 dogs are likely to be affected with this form of PRA, and an 18% carrier frequency within the LA population."

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 613581 Disease · OMIM 616152 Gene · OMIM 607056

Source: OMIA (Nicholas, Tammen & the Sydney Informatics Hub), entry OMIA:002289-9615, doi:10.25910/2AMR-PV70 (CC-BY 4.0).

The evidence

Published references

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

  2. The Blue Book: Ocular disorders presumed to be inherited in purebred dogs. 13th Edition · https://ofa.org/wp-content/uploads/2022/10/ACVO-Blue-Book-2021.pdf · 2021

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.

Predict a litter

Set each parent's status for Progressive Retinal Atrophy (Discovered in the Lhasa Apso; IMPG2-related PRA4) and see the odds for their puppies. Single recessive variant, exact Mendelian math.

Parent A
Parent B
NNClear
NmCarrier
NmCarrier
mmAffected
Clear25%
Carrier50%
Affected25%

These are the genetic odds for one known variant, not a promise: a real litter varies around them, and penetrance or other genes can change whether the condition ever appears. Use it to avoid pairing two carriers and to keep a line healthy, not to engineer a dog. Inheritance mode per OMIA.
Your breed

See what Progressive Retinal Atrophy (Discovered in the Lhasa Apso; IMPG2-related PRA4) looks like in your dog's breed.
Carrier frequency by breed

Top 3 well-sampled breeds (n ≥ 50)

Maximum 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.

0%3%5%
Lhasa Apso0.64% · n 233
Shih Tzu<0.1% · n 7,525
Yorkshire Terrier<0.1% · n 8,367
n = 16,125 dogs · Donner et al. 2023 carrier-screening cohort · Sniff Atlas
Each bar is one well-sampled breed; the whisker is its Wilson 95% CI, and fainter bars have wider intervals. Frequencies are population-level, not per-litter. Carrier status for Progressive Retinal Atrophy (Discovered in the Lhasa Apso; IMPG2-related PRA4) is measured; phenotype outcome depends on penetrance and modifiers.
▸ Full table with Wilson 95% confidence intervals
Breed Carrier frequency n tested
Lhasa Apso 0.64% 233
Shih Tzu <0.1% 7,525
Yorkshire Terrier <0.1% 8,367

263 additional breeds in the Donner 2023 cohort were tested but showed no carriers.

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 carrier 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:002289-9615.

  • 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:002289-9615 · Donner et al. 2023