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Canine Mendelian disease record

Early-onset PRA (Discovered in the Portuguese Water Dog; EOPRA)

Early-onset PRA (Discovered in the Portuguese Water Dog; EOPRA). Autosomal recessive. Observed in 1 of 266 breeds tested in the Sniff Atlas, with measured carrier frequencies drawn from 242,665 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:001521-9615
Autosomal recessive
Source dataset
Sniff Atlas v1.0.1 / DOI
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

This disorder was named 'Generalized PRA' in the review by Miyadera et al. (2012)

Clinical features

Lippman et al. (2007): "gPRA in Schapendoes is characterized by late onset and slow progression ... . Affected Schapendoes dogs appear normal when young, but develop gPRA at an age of onset between 2-5 years. Early in the disease, affected dogs are night-blind, lacking the ability to adjust their vision to dim light; later, their daytime vision also fails. This process of complete photoreceptor degeneration takes up to 2 years." Murgiano et al. (2020) describe the clinical signs in Portugese water dogs: "...visual deficits, including difficulty following moving objects and walking into still objects, which were reportedly worse under dim light, consistent with nyctalopia. These signs became progressively worse, compromising the animals’ vision under both dim and well-lit conditions. The age of onset was determined by the time point at which the visual deficits became noticeable to the owners or when ophthalmoscopic abnormalities were first noted. The male proband and the two affected females had decreased vision per the owner at initial presentation and were diagnosed ophthalmoscopically as EOPRA with an age of onset at 2 years. A second male dog had no obvious visual deficit per the owner at initial presentation at age 2 years and had unremarkable fundus when examined ophthalmoscopically. However, peripapillar changes suggestive of PRA developed by 3 years of age at which time electroretinography (ERG) was recommended but declined. This dog was re-examined at 6 years of age when visual impairment was evident, ERGs were undetectable ..., and ophthalmoscopic changes were consistent with mid-stage disease. The ophthalmoscopic changes observed were common in all affected dogs, characterized by generalized tapetal hyper-reflectivity, diffuse vascular attenuation, optic disc pallor, and multifocal depigmenta-tion of the non-tapetal fundus. .... A feature that was unique to this disease in all affected dogs was a distinct peripapillary ring of hyper-reflectivity or peripapillary conus ..., which progressed into a broader zone of hyper-reflectivity around the optic disc in advanced disease ... ."

Molecular genetics

Dekomien et al. (2010): "Mutation screening of the CCDC66 gene revealed a 1-bp insertion in exon 6 leading to a stop codon as the underlying cause of disease" for generalized progressive retinal atrophy on in the Schapendoes breed. Murgiano et al. (2020): "Whole‑genome sequencing in one affected [Portugese water] dog and its obligatory carrier parents identified a 1 bp insertion (CFA20:g.33,717,704_33,717,705insT (CanFam3.1); c.2262_c.2263insA) in CCDC66 predicted to cause a frameshift and truncation (p.Val747SerfsTer8). Screening of an extended PWD population confirmed perfect co‑segregation of this genetic variant with the disease. Western blot analysis of COS‑1 cells transfected with recombinant mutant CCDC66 expression constructs showed the mutant transcript translated into a truncated protein."

Pathology

Lippman et al. (2007): "Compared to a normal retina ..., the gPRA-affected eyes of a five year old Schapendoes displayed typical degeneration signs in peripheral and central areas ... . The outer retina with the photoreceptor layer and the outer nuclear layer was missing in all retinal parts investigated. The inner retina showed reduced inner nuclear and inner plexiform layers, whereas the ganglion cell layer appeared comparatively preserved."

History

Lippman et al. (2007) mapped generalized progressive retinal atrophy (gPRA) in the Schapendoes dogs to chromosome 20 and Dekomien et al. (2010) identified a 1-bp insertion in exon 6 leading to a stop codon as the likely cause of disease in this breed. Murgiano et al. (2020) investigated early‑onset progressive retinal atrophy (EOPRA) in Portugese water dogs, mapped EOPRA to chromosome 20 and identified a different 1 bp insertion in the CCDC66 gene associated with EOPRA.

Source: OMIA (Nicholas, Tammen & the Sydney Informatics Hub), entry OMIA:001521-9615, 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. Showing 6 of 7.

  3. 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 Early-onset PRA (Discovered in the Portuguese Water Dog; EOPRA) 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 Early-onset PRA (Discovered in the Portuguese Water Dog; EOPRA) looks like in your dog's breed.
Carrier frequency by breed

Top 1 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%1%2%
Portuguese Water Dog<0.1% · n 664
n = 664 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 Early-onset PRA (Discovered in the Portuguese Water Dog; EOPRA) is measured; phenotype outcome depends on penetrance and modifiers.
▸ Full table with Wilson 95% confidence intervals
Breed Carrier frequency n tested
Portuguese Water Dog <0.1% 664

265 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:001521-9615.

  • 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:001521-9615 · Donner et al. 2023