C116 - Congenital Stationary Night Blindness

The Briard dog is affected with an inherited retinal disorder characterized by congenital night blindness with various degrees of visual impairment under photopic illumination. Vision in affected dogs ranges from normal day vision to profound day blindness. The disease was initially described in Swedish (Briard) dogs as a stationary disorder analogous to human congenital night blindness. Congenital Stationary Night Blindness (CSNB) in Briard breed is caused by a mutation in the gene RPE65. RPE65 encodes a 65-kDA protein expressed exclusively in retinal pigment epithelium and is involved in the biochemistry of vision.

Since the disease shows an autosomal recessive mode of inheritance, two copies of the defective gene, one inherited from each parent, have to be present for a dog to be affected by the disease. Dogs 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.

A DNA-based test is now available for the detection of Congenital Stationary Night Blindness in Briards. This test utilizes molecular probes that are 100% specific for the detection of the gene (RPE65) associated with CSNB. Using the PCR, RPE65 is detected, amplified, and the results are interpreted to determine whether the mutation for CSNB is present in two copies (homozygous recessive), or whether the dog is a carrier of the mutation (heterozygous). Dogs that are diagnosed as having two copies of the mutation show clinical symptoms of the disease in as early as 5-6 weeks of age. Dogs that are diagnosed as carriers show no signs of the disease but are still 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, depending on the genetic standing of their mate. This test provides definitive information on the genetic status of this disease, giving breeders the information to eradicate the disease from their lines.