Progressive Retinal Atrophy, PRA4 (Lhasa Apso Type) is an inherited eye disease affecting dogs. Progressive Retinal Atrophy, PRA4 (Lhasa Apso Type) occurs as a result of degeneration of both Rod and cone type Photoreceptor Cells of the Retina, which are important for vision in dim and bright light, respectively. Age of onset is difficult to determine as the disease is progressive and owners may remain unaware of a clinically affected dog. The rod type cells are often first to degenerate and affected dogs will have vision deficits in dim light (night blindness) and loss of peripheral vision. Over time affected dogs continue to lose night vision and begin to show visual deficits in bright light. Other signs of progressive retinal atrophy involve changes in reflectivity and appearance of a structure behind the retina called the Tapetum that can be observed on a veterinary eye exam. Genetic testing may help clarify if a dog is affected with progressive retinal atrophy or another inherited condition of the eye.
Genetic testing of the IMPG2 gene will reliably determine whether a dog is a genetic Carrier of Progressive Retinal Atrophy, PRA4 (Lhasa Apso Type). Progressive Retinal Atrophy, PRA4 (Lhasa Apso Type) is inherited in an Autosomal Recessive manner in dogs. This means that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the IMPG2 gene mutation. Reliable genetic testing is important for determining breeding practices. To eliminate this mutation from breeding lines and avoid the potential of producing affected pups, breeding known carriers to each other is not recommended. Dogs that are not carriers of the mutation have no increased risk of having affected pups. However, because there are multiple types of progressive retinal atrophy (PRA) caused by mutations in other genes, a normal result in IMPG2 does not exclude PRA in a pedigree.
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
Hitti-Malin RJ, Burmeister LM, Ricketts SL, Lewis TW, Pettitt L, Boursnell M, Schofield EC, Sargan D, Mellersh CS. A LINE-1 insertion situated in the promoter of IMPG2 is associated with autosomal recessive progressive retinal atrophy in Lhasa Apso dogs. BMC Genet. 2020 Sep 7;21(1):100.