Progress retinal atrophy (PRA) is an encompassing name for a group of canine inherited retinal degenerations that affect many different breeds of dog and is the phenotypic equivalent of human retinitis pigmentosa (RP). There is no treatment to cure P/RA and no treatment to stop its progression; dogs affected with PRA invariably go blind. Mutations causing PRA in a small number of breeds have been identified and it is now firmly established that PRAs in different breeds are often caused by mutations in different genes. We have previously identified microsatellites in nine genes known to cause PRA in dogs or RP in humans.