A mutation (rdAc) in the CEP290 gene produces a defective protein that is associated with progressive retinal atrophy (PRA) in Abyssinian and related cats. The disease is characterized by progressive degeneration of the photoreceptors (rods and cones) in the retina. Affected cats typically develop late onset blindness; having normal vision at birth but developing clincal signs at 1 to 2 years of age (detectable by eye examination) and blindness by 3 to 5 years. However, age of disease onset and progression can be variable and some affected cats may not devolop clinical signs, and eventually blindness, until later in life (6+ years).
At the Molecular Diagnostic Unit, we have developed a PCR-based pyrosequencing assay to quickly and accurately identify the rdAc mutation known to cause PRA in Abyssinian and related breeds.
This assay will allow owners and breeders to identify affected and carrier cats and will enable them to inform breeding programs to reduce PRA (rdAc) in their kittens.
|Abyssinian||American Curl||American Wirehair||Balinese|
|Bengal*||Colourpoint Shorthair||Cornish Rex||Javanese|
* see below for more details about Bengal PRA
It is possible that Bengals may have the rdAc mutation since Abyssinians were used in the foundation of the breed, but if present this is likely to be at a low prevalence. Very recently a specific PRA mutation (PRA-b) was found in the Bengal breed and this mutation likely accounts for the majority of Bengal PRA cases. More information about Bengal PRA-b can be found here.
PRA is inherited as an autosomal recessive trait, meaning that two copies of the defective gene are required in a cat to produce the disease.
Carrier cats (those with a single copy of the defective gene; heterozygous) are not affected and have normal vision. However, breeding from two carrier cats has a 25% chance of producing affected kittens and a 50% chance of producing more carrier cats.
Therefore, it is NOT recommended to breed two carrier cats together, since this can produce affected kittens.
It is possible to continue to use carrier cats in breeding programmes to retain important breeding lines and to avoid reducing the size of the gene pool.
As long as carrier cats are mated to normal cats no affected kittens will be produced. This mating is likely to produce kittens that are carriers, which can be identified by genetic testing and, if necessary, future matings arranged with normal cats.
A Normal result on the PRA (rdAc) genetic assay means that the cat does not have the rdAc genetic mutation. It is possible that some cats may go on to develop retinal atrophy due to other, as yet unidentified, genetic mutations.
A Heterozygous result on the PRA (rdAc) genetic assay means that the cat carries one copy of the rdAc genetic mutation. This cat is a carrier of PRA.
A Homozygous result on the PRA (rdAc) genetic assay means that the cat carries two copies of the rdAc genetic mutation and will be affected by PRA.
Each certificate we issue will specify whether the cat is Normal, Heterozygous or Homozygous for the PRA (rdAc) mutation.
The gene test will help breeders decide whether or not to use cats for breeding. Generally homozygous affected cats should not be used for breeding because they are certain to pass on the genetic mutation. There is a 25% probability of two carrier (heterozygous) cats producing affected (homozygous) kittens. Breeding carrier and normal cats will produce around 50% normal and 50% carrier kittens.
This strategy can be used as part of a breeding programme to gradually eliminate the defective gene from the affected populations.