Progressive retinal atrophy 4 in Lhasa Apso

Progressive retinal atrophy (PRA) is a large group of inherited diseases that are the leading cause of blindness in various dog breeds. Individuals affected by PRA show a similar sequence of clinical abnormalities during the disease progression. Symptoms begin with night blindness followed by progressive loss of daytime vision and eventual blindness in all light conditions. Routine eye examinations reveal a progressive loss of photoreceptor cells in the retina due to their degeneration or retinal atrophy, which gives the name to the disease.

In Lhasa Apso, the disease is referred to as PRA4 and is caused by a LINE-1 insertion in the gene for the IMPG2 proteoglycan, which is thought to promote the growth and maintenance of photoreceptors.

The mode of inheritance of the mutation is autosomal recessive. This means that only individuals who inherit the mutated gene from both parents will develop the disease. Carriers of the mutated gene are clinically healthy but pass the mutation on to their offspring. In the case of a mating between two heterozygous individuals, theoretically 25% of the offspring will be completely healthy, 50% of the offspring will be carriers and 25% of the offspring will inherit the mutated gene from both parents and will therefore be affected by the disease.

The genetic test can clearly reveal the genotype of the animal and is a useful tool for breeders to prevent unintentional breeding of affected puppies.

.

Reference:

Hitti-Malin, R.J., Burmeister, L.M., Ricketts, S.L., Lewis, T.W., Pettitt, L., Boursnell, M., Schofield, E.C., Sargan, D., Mellersh, C.S. : A LINE-1 insertion situated in the promoter of IMPG2 is associated with autosomal recessive progressive retinal atrophy in Lhasa Apso dogs. BMC Genet 21:100, 2020. Pubmed reference: 32894063