Dominant Progressive Retinal Atrophy (RHO gene)

Progressive retinal dominant atrophy (APRD) is a disease that causes degeneration of the photoreceptor cells and consequently, loss of vision. APRD is caused by a mutation in the rhodopsin (RHO) gene.

Symptoms

Loss of night vision is one of the earliest clinical signs of APRD, and begins to become evident from 12-18 months of age. Dogs also experience a slow recovery of rod photoreceptor function after exposure to light. Over time, disease progression may lead to blindness.

Disease Management

There is currently no cure or treatment for progressive dominant retinal atrophy, but there are some options to help slow the progression of the disease as much as possible. One of the most effective tools is to adapt the dog's environment and routines to the vision loss, such as using gates to block stairs or avoiding moving furniture around. The use of antioxidants seems to have a beneficial effect on slowing down the disease, but more research is still needed to obtain a conclusive result.

Genetic basis

This disease follows an autosomal dominant mode of inheritance. Autosomal dominant inheritance means that dogs only have to inherit one copy of the mutation or pathogenic variant to be at risk of developing the disease. Each puppy born to a parent carrying one copy of the mutation has a 50% chance of inheriting one copy of the mutation and being at risk for the disease. Breeding between dogs carrying genetic variants that can cause disease is not recommended, even if they do not show symptoms.

Technical report

The RHO gene encodes rhodopsin, a light-activated receptor involved in rod-mediated night vision. In the study by Kijas et al. (2002), they identified English Mastiffs suffering from APRD caused by a mutation in the RHO gene (c.11C>G). The variant consists of a C to G transversion, a nonsense mutation, leading to the change of threonine to arginine in the extracellular domain of the protein. Subsequent to this study, 16 different breeds were tested that also had APRD, however, none carried the described c.11C>G mutation. Consequently, it is possible that the variant is present only in the English Mastiff breed, but a study involving a larger population of breeds is required to make this claim evident.

Most affected breeds

Bull Mastiff
English Mastiff

Bibliography

Kijas JW, Cideciyan AV, Aleman TS,et al. Naturally occurring rhodopsin mutation in the dog causes retinal dysfunction and degeneration mimicking human dominant retinitis pigmentosa. Proc Natl Acad Sci U S A. 2002 Apr 30;99(9):6328-33.

Kijas JW, Miller BJ, Pearce-Kelling SE,et al. Canine models of ocular disease: outcross breedings define a dominant disorder present in the English mastiff and bull mastiff dog breeds. J Hered. 2003 Jan-Feb;94(1):27-30.