Macular Corneal Dystrophy (MCD) in Labrador Retrievers

Macular Corneal Dystrophy (MCD)

Many different types of hereditary eye conditions have been described in the Labrador Retriever. During the ECVO eye examination, the dog’s eyes are checked for the presence of a large number of these inherited eye disorders, one of which is Macular Corneal Dystrophy (MCD). In this article, we explain what MCD is, how it is inherited, and what breeders can do to prevent this condition.

Macular Corneal Dystrophy (MCD) is a form of corneal dystrophy, a disorder of the cornea. The cornea is the outer, transparent part of the eye and plays an important role in focusing images. It is about half a millimeter thick and consists of three layers. In corneal dystrophy, substances such as fats and cholesterol accumulate in one of these layers. Depending on the exact location in the cornea, the disorder is referred to as macular, epithelial, or stromal.

Symptoms

In MCD, small accumulations of glycosaminoglycans (a specific type of carbohydrate) form in the middle layer of the cornea, the stroma. These deposits result in small whitish-grey spots and clouding of the cornea. In some cases, blood vessels can grow toward these spots. Fortunately, the condition itself is not painful, but vision is impaired. Over time, more whitish-grey spots may appear, or existing spots may merge. This further worsens vision, although it seems that the dogs do not become completely blind—at least, this has not been clearly described in scientific publications. Dogs with MCD may become insecure due to their deteriorating vision.

The condition often comes to light (without an ECVO eye exam) when the dog is between 4,5 and 6 years old. With an ECVO examination, it can become visible somewhat earlier. Although MCD in the Labrador Retriever strongly resembles the human version, Labradors fortunately do not develop blisters on the cornea, and the outer layer of the cornea remains healthy.

How does Macular Corneal Dystrophy develop?

Macular Corneal Dystrophy is caused by an autosomal recessive mutation in the CHST6 gene. This gene is also sometimes referred to as LOC489707. An autosomal recessive mutation means that only affected dogs (with two mutated genes) show symptoms. Carriers (with one mutated gene and one normal gene) do not develop symptoms but can pass on the mutated gene to their offspring.

Currently, it appears that only one mutation is responsible for the development of MCD in the Labrador Retriever, and that there are no other variants. This mutation is also found in dogs that descend from the Labrador, such as the (Australian) Labradoodle.

My Labrador is affected by or a carrier of MCD, what to do?

With the help of a DNA test, it is possible to determine whether your Labrador Retriever is clear, a carrier, or affected by MCD. Fortunately, almost all Labrador Retrievers in the Western Europe are free from this mutation, but carriers and affected individuals are still occasionally found, this is less than 1% of the Labrador Retriever population (2025). If a carrier is used for breeding it is important that it is only crossed with a dog that is proven to be free of MCD. This prevents the birth of affected puppies.

If your dog is affected by Macular Corneal Dystrophy, the appearance of spots on the cornea cannot be prevented. At present, there is also no effective treatment available that can (permanently) reduce corneal clouding or prevent your dog’s vision from worsening over time. Creating favorable breeding combinations using a DNA test is therefore especially important in preventing Macular Corneal Dystrophy.

Relevant tests

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