There is a hereditary eye disease historically described in the Berger de Brie, or Briard, and particularly well-documented in this breed: congenital stationary night blindness, or CSNB.

It has been described in scientific literature since the 1980s, its molecular mechanism has been identified, and a genetic test is available.

In breeding, its prevention relies on rigorous screening of breeding dogs.

What is CSNB?

CSNB is a hereditary retinal disorder with autosomal recessive inheritance.

It impairs vision in low light from the first months of life.

In its initial form, affected dogs can behave almost normally in bright light, but become significantly distressed as the light dims.

Progressive retinal degeneration can occur with age in some cases.

In dogs, the Briard is the breed in which this condition was first described. This particularity makes it a particularly important disease to be aware of for this breed, both in breeding and at the time of adoption.

The RPE65 mutation:

The molecular cause identified in the Briard concerns the RPE65 gene, which codes for a protein essential to the visual cycle in the retinal pigment epithelium.

The described mutation is a four-nucleotide deletion in exon 5, causing a frameshift and the appearance of a premature stop codon.

The result is a non-functional protein, unable to properly perform its role in visual physiology.

This same mutation has been found in Briards from several countries, including the United States, Canada, Sweden, and France. This supports a founder effect: it is likely an ancient mutation, transmitted from a common ancestor, and then spread throughout the global population of the breed.

This point is important, as it shows that we are not dealing with isolated cases that appeared independently in different breeding lines, but with a well-identified genetic anomaly specific to the history of the breed.

The RPE65 mutation in the Briard has also served as a model in research on certain ocular gene therapies.

Clinical signs

An affected puppy may appear hesitant, clumsy, or anxious as soon as the light diminishes. They may bump into things, refuse to move forward in dim light, and lose their bearings in poorly lit environments. In contrast, in bright light, their behavior may be almost normal, which sometimes delays the detection of the problem.

In the early years, the fundus may remain normal.

The reference examination to objectively assess functional impairment is the electroretinogram (ERG), which highlights a marked impairment of scotopic responses.

With age, signs of retinal degeneration may appear.

Genetic testing and responsible breeding

An DNA test to identify the RPE65 mutation is available in specialized laboratories.

It allows distinguishing between healthy dogs, healthy carriers, and affected dogs.

This test is a central tool for selection in responsible breeding.

The objective is not only to avoid the birth of affected puppies but also to manage reproduction with enough rigor to limit the spread of the mutated allele without unnecessarily depleting the genetic diversity of the breed.

Before acquiring a Briard puppy, requesting the genetic test results of both parents is a basic precaution.

In summary

Disease: hereditary retinal disorder with autosomal recessive inheritance

Gene involved: RPE65

Main signs: difficulty seeing in low light from the first months

Diagnosis: ERG + genetic test

Prevention: rigorous genetic screening of breeding dogs

Sources

1. Narfström K, Wrigstad A, Nilsson SE. The Briard dog: a new animal model of congenital stationary night blindness. Br J Ophthalmol, 1989. PubMed 2804031

2. Aguirre GD et al. Congenital stationary night blindness in the dog: common mutation in the RPE65 gene indicates founder effect. Mol Vis, 1998. PubMed 9808841

3. Bechynóvá R et al. Mutation in the RPE65 gene causing hereditary retinal dystrophy in the Briard dogs. Czech J Anim Sci, 2008. DOI: 10.17221/372-CJAS