Macular corneal dystrophy is an inherited, progressive eye disease affecting dogs. Affected dogs frequently present around 4 to 6 years of age with clouding of their corneas accompanied by pinpoint white to gray spots made up of an accumulation of a carbohydrate known as glycosaminoglycan. Some affected dogs will also display growth of new blood vessels across the surface of their corneas. The disease will typically progress to compromise vision.
Genetic testing of the CHST6 gene will reliably determine whether a dog is a genetic Carrier of macular corneal dystrophy. Macular corneal dystrophy is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the CHST6 gene mutation. Reliable genetic testing is important for determining breeding practices. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Dogs that are not carriers of the mutation have no increased risk of having affected pups.
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
Tetas Pont R, Downs L, Pettitt L, Busse C, Mellersh CS. A Carbohydrate Sulfotransferase-6 (CHST6) gene mutation is associated with Macular Corneal Dystrophy in Labrador Retrievers. Vet Ophthalmol. 2016 Nov;19(6):488-492.