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X-Linked Progressive Retinal Atrophy 1 (RPGR gene, Samoyed and Siberian Husky)

X-Linked Progressive Retinal Atrophy 1 (RPGR gene, Samoyed and Siberian Husky)

X-linked progressive retinal atrophy 1 is an eye disease caused by degeneration of the rods and cones, which are the photoreceptor cells of the retina. These cells are essential for vision in dim and bright light, respectively. This hereditary pathology is caused by mutations in the RPGR gene located on the X sex chromosome.

Symptoms

The first signs of disease may be seen at 1 year of age on an ophthalmologic examination, called an electroretinogram. However, visual deficits may not become evident until dogs are at least 2 years of age. The first cells to degenerate are the rods, so dogs first experience vision deficits in dim light, known as night blindness. As the disease progresses, the next cells to degenerate are the cones that respond to bright light, eventually producing total blindness.

Disease Management

There is no treatment for progressive vision loss. Thanks to their acute senses of smell and hearing, dogs can compensate for this loss, especially in familiar environments. You can help your dog by establishing regular exercise routes and gradually introducing the necessary changes.

Genetic basis

This disease follows an X-linked recessive mode of inheritance. Recessive X-linked inheritance means that female dogs must receive two copies of the mutation or pathogenic variant (one from each parent) to develop the disease, whereas males need only one copy of the mutated gene or variant from the dam to develop the disease. Male dogs usually show symptoms of the disease. Each male puppy born to a mother carrying the mutation has a 50% chance of inheriting the mutation and thus the risk of developing the disease. Bitches that do not carry the mutation are not at increased risk of having affected puppies. Breeding between dogs carrying genetic variants that can cause disease, even if they do not show symptoms, is not recommended.

Technical report

The RPGR gene codes for a protein called "regulatory retinitis pigmentosa GTPase". Mutations in this gene are primarily responsible for X-linked retinitis pigmentosa in humans and also in dogs, a disease that causes retinal degeneration and vision loss. The RPGR gene is expressed in the retina and is thought to produce a protein that interacts with other molecules to form complexes and is essential for the formation of the cilia of photoreceptor cells (cones and rods) as well as their maintenance and function. Zhang et al. were the first to identify the mutation responsible for X-linked progressive retinal atrophy in Samoyed and Siberian Husky dogs. The variant c.3416_3420del, in particular, causes a 5-nucleotide deletion (GAGAA) in the RPGR gene sequence.

Most affected breeds

Samoyed
Siberian Husky
Weimaraner

Bibliography

Appelbaum T, Santana E, Aguirre GD. Critical Decrease in the Level of Axon Guidance Receptor ROBO1 in Rod Synaptic Terminals Is Followed by Axon Retraction. Invest Ophthalmol Vis Sci. 2020 Mar 9;61(3):11.

Zhang Q, Acland GM, Wu WX,et al. Different RPGR exon ORF15 mutations in Canids provide insights into photoreceptor cell degeneration. Hum Mol Genet. 2002 May 1;11(9):993-1003.