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 underly the disease in the US population and research at the Animal Health Trust has confirmed that the same defect causes CSNB in UK Briards.
Possible results for a Briard following the CSNB test:-
N = Normal Can be bred to any Briard Will never develop CSNB
C = Carrier Carrier of CSNB Will never develop CSNB can be bred to a
Briard that is clear of CSNB without any of the off spring ever being affected by CSNB.
A = Affected Homozygous for CSNB Will develop CSNB
A Briard that is genetically clear of CSNB at the present time does not need to be tested, I.e if both parents eye status is normal..