Progressive Retinal Atrophy (SAG gene, Basenji)

Progressive retinal atrophy is an eye condition in which a gradual loss of vision is experienced due to degeneration of the photoreceptor cells (cones and rods) in the retina.

Symptoms

One of the first clinical symptoms seen in progressive retinal atrophy is loss of night vision, as daytime vision degeneration usually takes longer to manifest and leads to complete blindness. In addition, this eye disorder has other distinctive signs, such as changes in the appearance of the eyes, which may include clouding, grayish hue and a slight abnormal sheen. Affected dogs tend to bump into objects more easily and may experience retinal cataracts as a result of disease progression.

Disease Management

The management of progressive retinal atrophy in dogs aims to improve the quality of life of the affected dog, even though there is no curative treatment for this disease. However, measures can be taken to ensure a suitable environment, such as keeping furniture and objects in place, which facilitates the dog's adaptation to the disease.

Genetic basis

This disease follows an autosomal recessive mode of inheritance. Autosomal recessive inheritance means that the dog, regardless of sex, must receive two copies of the mutation or pathogenic variant to be at risk of developing the disease. Both parents of an affected dog must carry at least one copy of the mutation. Animals with only one copy of the mutation are not at increased risk of developing the disease, but may pass the mutation on to future generations. Breeding between dogs carrying genetic variants that can cause disease, even if they do not show symptoms, is not recommended.

Technical report

Progressive retinal atrophy is an inherited disorder belonging to a group of retinal diseases characterized by the gradual degeneration of the rods, leading to night blindness and loss of peripheral vision. Subsequently, degeneration of the cones occurs, resulting in loss of central vision and, ultimately, total blindness. A correlation has been established between the SAG gene and the development of this ocular condition. The SAG gene encodes a protein known as arrestin that plays a crucial role in the phototransduction cascade of retinal photoreceptors. A mutation (c.1216T>C) has been identified as the likely cause of progressive retinal atrophy in the Basenji breed. The substitution involves the replacement of a normal stop codon by the amino acid arginine, which involves the addition of 25 amino acids to the normal protein. It is important to note that there are several forms of progressive retinal atrophy and different genes have been identified in dogs that could be related to this condition. At the moment, not all variations described to date are included in our test.

Most affected breeds

Basenji

Bibliography

Goldstein O, Jordan JA, Aguirre GD,et al. A non-stop S-antigen gene mutation is associated with late onset hereditary retinal degeneration in dogs. Mol Vis. 2013 Aug 27;19:1871-84. PMID: 24019744; PMCID: PMC3762564.