Progressive Retinal Atrophy, Early Onset (Spanish Water Dog Type)

Other Names: PRA-EO
Affected Genes: PDE6B
Inheritance: Autosomal Recessive
Mutation: chr3:92358235-92358240 (canFam4): 6 bp deletion (CCAGAA)

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Common Symptoms

Early-onset progressive retinal Atrophy is an inherited eye disease affecting Spanish water dogs. Early-onset progressive retinal atrophy occurs as a result of degeneration of both Rod and cone type Photoreceptor Cells of the Retina, which are important for vision in dim and bright light, respectively. Affected dogs may present with vision problems from as early as 1.5 years of age, with significant loss of vision by 4.5 years of age. The rod type cells are affected first and affected dogs will initially have vision deficits in dim light (night blindness) and loss of peripheral vision. Over time affected dogs continue to lose night vision and begin to show visual deficits in bright light. Other signs of progressive retinal atrophy involve changes in reflectivity and appearance of a structure behind the retina called the Tapetum that can be observed on a veterinary eye exam. Genetic testing may help clarify if a dog is affected with progressive retinal atrophy early onset or another inherited condition of the eye.

Breed-Specific Information for the Spanish Water Dog

The Mutation of the PDE6B gene associated with early-onset progressive retinal Atrophy has been identified in the Spanish water dog. Though the exact frequency in the overall Spanish water dog population is unknown.

Testing Tips

Genetic testing of the PDE6B gene in Spanish water dogs will reliably determine whether a dog is a genetic Carrier of early-onset progressive retinal Atrophy. Early-onset progressive retinal atrophy is inherited in an Autosomal Recessive manner in dogs. This means that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the PDE6B gene mutation. Reliable genetic testing is important for determining breeding practices. To eliminate this mutation from breeding lines and avoid the potential of producing affected pups, breeding known carriers to each other is not recommended. Spanish water dogs that are not carriers of the mutation have no increased risk of having affected pups. However, because there are multiple types of progressive retinal atrophy (PRA) caused by mutations in other genes, a normal result in PDE6B does not exclude PRA in a pedigree.

There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.


  • Winkler PA, Ramsey HD, Petersen-Jones SM. A novel mutation in PDE6B in Spanish Water Dogs with early-onset progressive retinal atrophy. Vet Ophthalmol. 2020;00:1–5. [PubMed: 32639685]