Congenital Stationary Night Blindness in BriardS
Congenital Stationary Night Blindness (csnb) in Briards, also called hereditary retinal dystrophy, is an inherited disease caused by a defect in the gene RPE65. The symptoms include night blindness and a loss of vision in daylight that can vary between individual dogs. The disease shows an autosomal recessive mode of inheritance; therefore two copies of the defective gene, one inherited from each parent, have to be present for a dog to be affected by the disease. Individuals with one copy of the defective gene and one copy of the normal gene - called carriers - show no symptoms but can pass the defective gene onto their offspring. When two apparently healthy carriers are crossed, 25% (on average) of the offspring will be affected by the disease with a further 50% themselves being carriers.
The genetic defect underlying this condition was first identified in the Swedish population of Briards as a deletion of a small segment of the DNA within the gene for RPE65, a protein involved in the biochemistry of vision. The same defect was subsequently shown to underlie the disease in the US population and our research has confirmed that the same defect causes csnb in UK Briards. We are now offering a DNA test for this disease distinguishing affected, carrier and normal individuals. The test probes directly the DNA of the RPE65 gene and provides definitive information on the genetic status of this disease, giving breeders the information to eradicate the disease from their lines.
The test diagnoses Briards affected with this disease but can also detect those dogs which are carriers, showing no symptoms of the disease but able to produce affected pups if mated to another carrier. It is important that carrier dogs are still bred with clear dogs, especially in the first few generations of a new DNA test being launched for a condition. Through this, breeders can capture the desired traits of the breeding dogs, and then, at a point in the future, if two dogs are genuinely comparable, can choose the clear dogs over the carriers.
Breeders will be sent results identifying their dog as belonging to one of three categories:
CLEAR: The dog has two copies of the normal gene and will neither develop csnb, nor pass a csnb gene to its offspring.
CARRIER: The dog has one copy of the normal gene and one copy of the mutant gene that causes csnb. It will not develop csnb but will, if bred from, pass on the mutant gene to, on average, 50% of its offspring.
AFFECTED: The dog has two copies of the mutant gene that causes csnb and will develop the disease.
Tests can be ordered through our Webshop.