Primary Open Angle Glaucoma (POAG) in Basset dog breeds

Primary open angle glaucoma or POAG for short is a hereditary eye condition that has been identified to be present as a gene mutation in various breeds of dog of the Basset type. The condition leads to a gradual increase in the pressure within the eye itself, which is both painful and can ultimately cause blindness.

The condition means that inter-ocular pressure in the eye progressively rises due to a genetic defect, and the eye is unable to release the fluids that are necessary to naturally return the eyes to normal pressure. This in turn leads to death of the retinal ganglion cells, which are the nerve cells that accept visual information via the retina, in turn passing them via the optic nerve to the brain where they are interpreted into vision.

Death of the retinal ganglion cells results in blindness, which cannot be reversed or corrected.

The condition usually becomes apparent in dogs that have inherited the affective form of the condition when they are still relatively young, usually anywhere between eight and eighteen months of age. The initial symptoms of the condition can easily be confused with other problems such as allergies or conjunctivitis, as the eyes will appear red, inflamed and irritated, leading to the dog pawing at their eyes and rubbing them excessively to try to get some relief.

While the condition can sometimes be treated if it is diagnosed and intervention begins quickly, this is not always possible, and only viable for a fairly narrow window of time after the condition has begun to develop.

As a hereditary health condition, the markers of the disease can be identified by DNA analysis, and in breeds considered to be at risk of primary open angle glaucoma, finding out the dog’s status is important. This can help to ensure that dogs that can pass on the condition are not used for breeding, and also, gives dog owners a better chance of early diagnosis and so, potentially successful treatment.

In this article, we will look at primary open angle glaucoma in dogs in more detail, including what sort of dogs can inherit the condition, how the heredity of the condition works, and how to get your dog tested for the condition.

More about primary open angle glaucoma

Glaucoma is a relatively well known and well understood eye condition that can affect both dogs and a variety of other animals too, including humans. Glaucoma comes in two forms, known as primary and secondary. Primary glaucoma occurs on its own without the need for something to trigger the condition, such as another health condition or an accident, while secondary glaucoma occurs as a secondary complication such as another eye problem or an injury.

As the name indicates, primary open angle glaucoma is one of the primary forms of the condition, as it occurs due to a hereditary defect (gene mutation) rather than due to an outside cause.

What sort of dogs can be affected by the condition?

Primary open angle glaucoma has been identified in the UK within the gene pools of several pedigree dog breeds, including the Petit basset griffon vendeen, the Basset hound, and the Basset Fauvre de Bretagne. This means that any dog from one of the affected breeds may potentially carry or be affected by the condition, as can non-pedigree dogs that share ancestry with one of the affected breeds.

How does the heredity of the condition work?

Primary open angle glaucoma is an autosomal recessive hereditary condition, which means that whether or not any given dog will inherit the disorder depends on the combination of genes that they inherit from their two parent dogs. As an autosomal recessive condition, the combination of genes inherited from both sides of the breed line are what dictates the status of any given dog, rather than the status of one of the parent dogs on their own.

Dogs are notated as either clear, carrier or affected, and it is important to note that carrier dogs will not be affected by the condition themselves, and so may not be identified as a carrier and still used for breeding unknowingly. This is why testing is so important, even for ostensibly healthy dogs.

The heredity of the condition can best be outlined as follows:

• Two clear dogs will have clear puppies.
• Two affected dogs will have affected puppies.
• Two carriers will produce mixed odds for each of their puppies of 50% carrier, 25% affected and 25% clear.
• A clear dog and a carrier will produce 50% carriers and 50% clear.
• A clear dog and an affected dog will produce a litter of carriers.
• A carrier and an affected dog will produce 50% carriers and 50% affected.

How can you get your dog tested?

In order to find out your dog’s status you will need to ask your vet to take a DNA sample from your dog, which can be in the form of a blood sample, cheek swab or clipping from the dog’s dewclaw.

This is then sent off to one of The Kennel Club’s approved laboratories for testing, and they will then return the status result for your dog to you.