Progressive retinal Atrophy (bullmastiff/mastiff type) is an inherited eye disease affecting bullmastiffs and mastiffs. Progressive retinal atrophy (bullmastiff/mastiff type) occurs as a result of degeneration of Rod type Photoreceptor Cells of the Retina, important for vision in dim light. Initial clinical 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. Affected dogs initially present by 18 months of age with vision loss in dim light (night blindness) and loss of peripheral vision. The visual deficits gradually progress to complete vision loss. Dogs that inherit two RHO mutations have a more rapid disease progression than dogs that have only inherited one Mutation. The disease follows a variable progression and severity depending on the individual, but complete degeneration of the retina can take years.
Genetic testing of the RHO gene will reliably determine whether a dog is a genetic Carrier of progressive retinal Atrophy (bullmastiff/mastiff type). Progressive retinal atrophy (bullmastiff/mastiff type) is known to be inherited in an Autosomal Dominant manner in dogs meaning that dogs only need to inherit one copy of the mutated gene to be at-risk for the disease. Dogs that inherit two copies of the genetic Mutation are at-risk of developing a more severe form of the disease. Each pup that is born to a parent carrying one copy of the mutation has a 50% chance of inheriting one copy of the RHO gene mutation and being at-risk for the disease. If both parents are affected, the chance of having affected offspring increases to 75-100% depending on whether the parents carry one or two copies of the mutation. Because symptoms may not appear until adulthood, genetic testing should be performed before breeding. Reliable genetic testing is important for determining breeding practices. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers is not recommended. Dogs that are not found to have this specific mutation have no increased risk of having affected pups for the autosomal dominant type of PRA. However, because there are multiple types of PRA caused by mutations in other genes, a normal result in RHO 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.
Kijas JW, Cideciyan AV, Aleman TS, Pianta MJ, Pearce-Kelling SE, Miller BJ, Jacobson SG, Aguirre GD, Acland GM. Naturally occurring rhodopsin mutation in the dog causes retinal dysfunction and degeneration mimicking human dominant retinitis pigmentosa. Proc Natl Acad Sci U S A. 2002 Apr 30; 99(9):6328-33.
Kijas JW, Miller BJ, Pearce-Kelling SE, Aguirre GD, Acland GM. Canine models of ocular disease: outcross breedings define a dominant disorder present in the English mastiff and bull mastiff dog breeds. J Hered. 2003 Jan-Feb; 94(1):27-30.