Progressive Retinal Atrophy 4 is one of a number of PRAs to have been discovered in many breeds of dog. Like many other PRAs, this appears to be a breed-specific disease/mutation. Symptoms are typical of other PRAs in that the dog has normal vision at birth, and then progresses to complete blindness. This condition has previously been identified in the breed using clincal eye examinations, the data from which this DNA test was developed. Discovered by the Animal Health Trust (AHT), the PRA4 mutation has so far been found to be unique to the Lhasa Apso. According to the AHT, 354 dogs tested from the UK population generated a carrier frequency of approximately 17% in their UK DNA testing cohort between 2017-18 test development. ?The frequency of the PRA4 allele is 0.09 which corresponds to the frequency of affected Lhasa Apso?s in this UK population as 0.009.?[From AHT website, Feb 2020]. Autosomal Recessive inheritance.