Rod-Cone dysplasia 1a (PDE6B gene)

Cone and rod dysplasia type 1a (CRD1a) is an eye disease caused by a mutation in the PDE6B gene, which is crucial for the normal function of photoreceptor cells (cones and rods) in the retina.

Symptoms

Dogs with CRD1a usually show signs of vision loss around 2 to 3 years of age. Progression of the disease is usually slow. At first, dogs may have difficulty seeing in low light conditions, known as night blindness, but as the disease progresses, daytime vision loss occurs.

Disease Management

Unfortunately, there is no cure for cone and rod dysplasia. Management of the disease focuses on helping dogs adapt to their vision loss, which may include teaching them to respond to auditory cues and modifying their environment to make it safe. If your dog shows any symptoms, you should see your veterinarian for an evaluation.

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

Cones and rods are the cells in the retina that detect external light and transmit the information to the brain, where it is interpreted into vision. Cones are responsible for color vision and fine detail in bright light, while rods are involved in vision in low light conditions. In cone and rod dysplasia, both cells are affected, resulting in a progressive loss of vision that evolves rapidly over the first few months of life. Retinal dysplasia can be genetic in origin, but it can also be acquired and due to other factors such as viral infection. CRD1a is caused by mutations in the PDE6B gene, which codes for the beta subunit of phosphodiesterase, an enzyme of the photoreceptor cell membrane that is crucial for its participation in the phototransduction cascade. Here, we analyzed a variant in the PDE6B gene identified in the Sloughi race. This variant involves an insertion (c.2448_2449insTGAAGTCC) that causes the introduction of a stop codon, resulting in the formation of a protein truncated at 40 amino acid residues. A variant in the PDE6B gene associated with the development of CRD1 has also been described in the Irish Setter breed.

Most affected breeds

Sloughi

Bibliography

Dekomien G, Runte M, Gödde R, Epplen JT. Generalized progressive retinal atrophy of Sloughi dogs is due to an 8-bp insertion in exon 21 of the PDE6B gene. Cytogenet Cell Genet. 2000;90(3-4):261-7.