Test Detail

rdy-PRA is a form of hereditary retinal dystrophy of the cat with dominant inheritance and very early onset. It affects the development of the photoreceptors themselves, which do not form normally (rod and cone dysplasia) and degenerate rapidly. Affected kittens lose vision in the first months of life and become blind young. Unlike rdAc, a single copy of the allele is enough to cause the disease.

Classically associated with the Abyssinian and present in related breeds such as the Ocicat and the Somali. Thanks to genetic control and the removal of affected lines, it is now considered uncommon. Current frequencies are difficult to estimate: limited data.

- Very low vision from the first weeks of life
- Marked disorientation or clumsiness in young kittens
- Mydriasis with increased tapetal reflection
- Markedly altered or abolished ERG at an early age
- Tapetal hyperreflectivity and vascular attenuation before the first year
- Complete blindness in young animals

It was described in the 1980s in Abyssinian cats as early retinal dysplasia, distinct from the late form in the same breed background; electrophysiological studies showed a markedly altered ERG from early ages. In 2010, Menotti-Raymond and colleagues identified the molecular cause: a single-nucleotide deletion in the CRX gene (Rdy allele) that causes a frameshift. Occelli et al. (2023) demonstrated that homozygotes (Rdy/Rdy) have a more severe phenotype than heterozygotes, so the inheritance is redefined as incomplete dominant. DNA testing allows the variant to be controlled in breeding populations.

- Test breeding animals of at-risk breeds: individuals with one copy (N/rdy) are affected and should not be bred.
- Breed only with N/N individuals.
- A positive individual produces, on average, 50% affected offspring per litter.
- Kittens from at-risk crosses should be tested and placed as companion animals with early adaptation to blindness.

Differentiate from rdAc-PRA (later onset), cortical blindness and nutritional retinopathies. In kittens ophthalmoscopy may be inconclusive at first; ERG detects early photoreceptor dysfunction. Blind cats can have a good quality of life indoors with stable routines and enrichment, but the disease seriously limits visual function from youth.

1. Menotti-Raymond M et al. (2010) Mutation discovered in a feline model of human congenital retinal blinding disease. Invest Ophthalmol Vis Sci 51(6):2852-2859. PMID: 20053974
2. Occelli LM et al. (2023) Cat LCA-CRX Model, Homozygous for an Antimorphic Mutation Has a Unique Phenotype. Transl Vis Sci Technol 12(6):15. PMID: 37351895
3. OMIA:000881-9685. Retinal atrophy - Rod-cone dysplasia, CRX related in Felis catus. https://omia.org/OMIA000881/9685/