Macular Corneal Dystrophy (MCD) in Labrador Retrievers

Macular Corneal Dystrophy (MCD) is an inherited eye disease in which glycosaminoglycans accumulate in the cornea. This affects its transparency, and the disease gradually leads to vison impairment. Clinical signs appear in middle-aged dogs (between 4.5 and 6 years old) and include a cloudy or hazy corneal opacity, small white-grey or yellowish-brown spots on the cornea and a gradual deterioration of vision.

The disease is caused by a missense mutation c.814C>A in the CHST6 gene (also known as LOC489707), which is involved in the metabolism of proteoglycans and ensures the correct structure of the cornea.

The mutation is inherited in an autosomal recessive manner. This means that the disease only develops in individuals who inherit the mutated gene from both of their parents. Carriers of the mutated gene are clinically healthy, but they pass the mutation to their offspring. In case of mating two heterozygous individuals, theoretically 25% of the offspring will be clear (without the mutation), 50% of the offspring will be carriers, and 25% of the offspring will inherit the mutated gene from both parents and will therefore be affected by this disease.

A genetic test can clearly reveal the genotype of the animal and is a suitable tool for breeders to prevent the unintentional reproduction of affected puppies.

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References:

Tetas Pont, R., Downs, L., Pettitt, L., Busse, C., Mellersh, C.S. : A carbohydrate sulfotransferase-6 (CHST6) gene mutation is associated with macular corneal dystrophy in Labrador Retrievers. Vet Ophthalmol 19:488-492, 2016. Pubmed reference: 26585178