rdAc progressive retinal atrophy is an inherited ocular disease of the cat that causes gradual and irreversible degeneration of the photoreceptors, first the rods and then the cones. It affects the visual system and progresses to complete blindness. Because the loss is slow, many cats adapt for years, but they fail in low light and progressively lose their independence. It is the form of feline PRA present in the most breeds and one of the most frequent in genetic panels.

Breed of origin: Abyssinian, with the closely related Somali. The variant has been detected in other breeds included in the panels (for example Bengal, Siamese, Oriental, Tonkinese, Singapura, Peterbald), generally with low but detectable carrier frequencies. The figures vary greatly between breeds, countries and years, and in breeds outside the Abyssinian group the published data are limited; a specific frequency should not be assumed without a population study.

- Initial night blindness (clumsiness in dim light)\n- Dilated pupils (mydriasis) with increased tapetal brightness\n- Progressive hyperreflectivity of the tapetum\n- Narrowing of the retinal vessels\n- Loss of daytime vision in advanced stages\n- Complete blindness at the end, without ocular pain

rdAc-PRA was clinically characterized in the Abyssinian cat in the 1980s, with ophthalmological and electrophysiological studies that defined it as a relatively late-onset progressive retinal degeneration. Molecular genetics identified the cause in the CEP290 gene: Menotti-Raymond et al. (2007) described in intron 50 the variant IVS50+9T>G (c.7584+9T>G), which creates a splice donor site and causes a 4-bp insertion with a frameshift and protein truncation. The earlier attribution to CRYBA1 was erroneous and was ruled out. The DNA test made it possible to detect the variant in many breeds outside the Abyssinian setting, probably due to common ancestry and the spread of carrier breeding animals.

- Perform the DNA test before the first mating: it distinguishes clear (N/N), carriers (N/rdAc) and affected (rdAc/rdAc).\n- A carrier can be mated to a clear animal without risk of affected cats; never to another carrier.\n- Keep at most one carrier of value per generation, always with a clear mate, and test the offspring intended for breeding.\n- Record the results in the pedigree to prevent the silent spread of the allele.

Differential diagnosis with taurine-deficiency retinopathy (bilateral lesions in the central area of the retina, reversible in early stages), other feline PRAs (rdy, pd), inflammatory chorioretinopathies and hypertensive retinopathy. Ophthalmoscopy and ERG help confirm and stage it. As there is no treatment, management is supportive: a stable environment, indoor life and annual ophthalmological follow-up.

1. Menotti-Raymond M et al. 2007. Mutation in CEP290 discovered for cat model of human retinal degeneration. Journal of Heredity. PMID: 17507457
2. Lyons LA. 2015. DNA mutations of the cat: the good, the bad and the ugly. Journal of Feline Medicine and Surgery. PMID: 25701860
3. OMIA:001244-9685. Retinal degeneration II (Felis catus). Online Mendelian Inheritance in Animals.