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 research at the Animal Health Trust has confirmed that the same defect causes csnb in UK Briards. The Animal Health Trust is 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 cannot only diagnose 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. It is important to eliminate such carriers from a breeding population since they represent a hidden reservoir of the disease that can produce affected dogs at any time.
Samples for testing (mouth swabs) should be sent, together with a completed DNA Testing form and payment of £54 inc VAT (cheque or credit card) for each sample to Genetic Services, Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk CB8 7UU.
DNA testing forms can also be downloaded by clicking here.
Enquiries should be made to Symone Ingram telephone +44 (0) 8700 509144 or fax +44 (0) 8700 502461 or via e-mail to dnatesting@aht.org.uk.
