Progressive retinal atrophy is the term used to describe a group of genetic disorders that result in degeneration and atrophy (loss or wasting) of the retina – the light-sensitive layer of cells at the back of the eye. This can lead to a progressive decline in the quality of vision and in some cases can lead to blindness. The human equivalent of this disease is known as ‘retinitis pigmentosa’.
Owners may become aware of this condition when vision becomes significantly impaired and, for example, the cat may start to become disorientated or bump into objects.
Cats affected by PRA
An autosomal dominant form of PRA characterised by rod-cone dysplasia (disease affecting both the rod and cone photoreceptor cells) and causing loss of vision by the time a cat reaches 12-16 months of age. The disease has been designated PRA-Rdy. The earliest signs of vision impairment may be seen in kittens as young as 4 weeks old with this disease. This is a rare condition and appears to be restricted to Abyssinians and Somalis. The gene has been identified (CRX) and tests are available
An autosomal recessive rod-cone degeneration. This is a later onset condition, with earliest signs being seen at around 1.5-2 years of age. After this there is progressive loss of vision, and complete blindness will occur around 3-4 years later. The disease has been designated PRA-rdAc. This form of disease is more prevalent than the autosomal dominant form and is present in Abyssinian and Somali cats. The responsible gene has been identified and is designated CEP290 – DNA tests for cats are available. This defect now appears to be present in a wide range of different breeds, including:
- American Curl
- American wirehair
- Cornish Rex
- Oriental shorthair
An autosomal recessive form of PRA has been identified in Persian cats with clinical signs being seen as early as 2-3 weeks of age and almost complete retinal degeneration by 4 months of age. The causative gene for this form of PRA has not yet been identified, but there is evidence that this may be relatively common in some populations of Persians. There was a belief that this was linked to certain coat colours in Persians, but studies have shown no evidence of this.
An early-onset form of PRA has also been described in mixed-bred (non-pedigree) cats, but this is thought to be rare.