PRA in Siamese Cats: Signs, Gene Testing and Living With Vision Loss

If you share your home with a Siamese cat, progressive retinal atrophy (PRA) is the eye condition worth knowing about. It slowly wears away the part of the eye that senses light, and the gene change behind it is more common in Siamese cats than in most other breeds studied [1][2][4].

What is PRA in cats?

• PRA is a group of inherited diseases of the retina, the light-sensing layer at the back of the eye [3][5].
• The retina's light-sensing cells slowly break down over time [3][5].
• Night vision usually goes first; later, sight in daylight is lost too, which can lead to blindness [3][5].

In Siamese cats, the known form is caused by a change in a gene called CEP290, often shortened to rdAc [1][2][4].

Is PRA inherited or contagious?

It's inherited, not contagious. A cat can't catch it from another cat [1][2][3].

• A cat develops the disease only if it inherits two copies of the gene change, one from each parent [2][4].
• A cat with one copy is a carrier. It stays healthy but can pass the gene to its kittens [2][4].
• Carriers show no signs, so the gene can pass quietly through a family line for generations [2][4].

Which cats are at risk?

In a large study of 41 breeds, the gene change was found in 16 of them. Siamese cats had one of the highest rates, with around a third of their gene copies carrying it in North American and European cats [1].

Close Oriental relatives of the Siamese are named alongside it as a related risk group: the Balinese, Colourpoint Shorthair, Javanese and Oriental Shorthair [1][2][4]. The gene change was first found in Abyssinian and Somali cats, and it has also been recorded in other breeds, including the Maine Coon and Ragdoll [1][2].

At what age do signs appear?

Affected kittens are born with normal sight [1]. The pace varies from cat to cat, but in the study above [1]:

• Eye changes could be seen by a vet at around 1 to 2 years of age.
• Cats had serious sight loss by around 5 to 6 years of age.

What are the signs a cat is losing its sight?

Early signs are easy to miss, because cats adapt well to a familiar home [3][5]. Signs to watch for include [5]:

• Poorer vision at night or in dim light.
• Unusually wide (dilated) pupils.
• Bumping into furniture, or seeming lost.
• Trouble finding food, water or the litter tray.
• Not wanting to use the stairs.
• Being less active at night.

PRA itself isn't described as painful for the cat [5].

See a vet promptly: If your cat loses its sight suddenly, rather than slowly, have it checked quickly. Vision loss can have other causes, such as high blood pressure, and some of them are urgent [3][5][6].

Only a licensed vet can tell what's behind these signs.

Is there a gene test for PRA?

Yes. A DNA test for the rdAc gene change is available through vet genetics laboratories, usually from a blood sample or a cheek swab [4]. It shows whether a cat is clear, a carrier, or affected [4].

• Gene testing is recommended for breeds known to be at risk [5].
• Affected cats should not be used for breeding [4][5].
• Breeders avoid pairing two carriers, because that can produce affected kittens [4].

What a test result means for your own cat is a question for your vet.

How do I help a blind cat at home?

Cats usually cope very well with sight loss, especially when it comes on slowly and home stays the same. They find their way using hearing, smell and their whiskers [3][5][6]. Helpful steps [6]:

• Keep the layout the same. Don't move furniture; your cat builds a map of the home in its head.
• Fix the essentials in place. Keep food, water, litter tray and bed in the same easy-to-reach spots, away from busy walkways.
• Block off hazards. Close off balconies, high ledges and stairs where a fall could happen, and keep toilet lids down.
• Keep things calm. Cut down sudden loud noises, and ask family members, including children, to move gently around the cat.
• Stay safe outdoors. If your cat used to go outside, keep it to a secure, enclosed space.

A blind cat doesn't need another pet for company. Your attention and a safe, interesting home matter most [6].

FAQ

Is PRA contagious between cats?

No. PRA is an inherited condition, not an infection, so it can't spread from one cat to another [1][2][3].

What should I ask a Siamese breeder about PRA?

Ask whether the parents were gene-tested for rdAc (PRA), and ask to see the results [4][5].

Can a cat have PRA without me noticing?

Yes, early on. Cats adapt well at home, so early sight loss is easy to miss. Watch for signs in dim light and ask your vet if you're unsure [3][5].

Do cats adapt to being blind?

Yes, they usually adapt very well, especially when sight fades slowly and the home stays the same [3][5][6].