Genetic tests in dogs: what CEA, TNS, MDR1 and PRA are and how to read the result

What is a genetic test in dogs?

It is a DNA analysis that looks for the mutation responsible for one specific inherited disease. It is done once in a lifetime, usually with a swab rubbed on the inside of the cheek, and the laboratory issues a certificate with the result. There is no general “genetic health” test: each one answers a single question.

Its value lies in breeding. Many of these diseases cannot be seen in the parents, because a dog can carry the mutation and be healthy. The test brings it to light before the mating. That is why it is done on the parent dogs and not on the puppy: the puppy inherits what its parents had.

What do clear, carrier and affected mean?

They are the three possible results for a recessive disease, which is the most common case. Clear: the dog does not have the mutation. Carrier: it has one copy, is healthy and can pass it on. Affected: it has two copies, one from each parent, and is the dog that develops or may develop the disease.

From there comes the rule summarized by Britain’s Royal Kennel Club:

A carrier, then, is neither a sick dog nor a poor parent. The FCI (Fédération Cynologique Internationale) breeding strategy, which the regulations of the ACCC (Asociación Club Canino Colombiano, Colombia’s FCI member kennel club) incorporate in their preamble, puts it this way: DNA tests should serve to avoid producing sick dogs, not necessarily to eradicate the disease, and a carrier should only be mated to a dog that is not one. Ruling out every carrier would reduce the breed’s diversity.

Which genetic tests apply to a Border Collie?

Five come up most often: CEA, TNS, CL, IGS and MDR1. The first four are recessive diseases that a test makes it possible to avoid entirely; the fifth is a drug sensitivity. All of them appear, along with a few more, on the list the Royal Kennel Club publishes for the breed.

MDR1 deserves a separate note. It is very common in the Collie and uncommon in the Border Collie: Washington State University, which runs the test, finds it in fewer than 5% of the Border Collies it tests. The problem drugs it lists include several commonly used antiparasitic medications. If your dog has had this test, whatever the result, your veterinarian needs to know it before prescribing.

Merle color is another genetic matter in the breed, with its own guide: merle Border Collie, colors and health.

Which tests apply to an Australian Cattle Dog?

Two DNA tests, both for the eyes: PRA-prcd and PLL. They are the ones the breed’s club in the United States recommends, according to the American Kennel Club, together with hip and elbow evaluation, an exam by an ophthalmologist and the BAER hearing test. Both diseases are recessive.

• PRA-prcd, progressive retinal atrophy. The cells of the retina degenerate: the dog first loses its night vision and ends up blind. It usually starts at around three years of age or later, by which time a dog may already have been bred.
• PLL, primary lens luxation. The fibers that hold the lens in place break and the lens shifts. It is painful and can lead to glaucoma and loss of vision. Complete luxation usually happens between three and eight years of age.

What DNA does not cover in this breed, congenital deafness, is explained in eye exams and the BAER test.

Which tests exist for the Bernese Mountain Dog and the Cavalier?

In the Bernese Mountain Dog, the test for degenerative myelopathy (DM), in its two variants. In the Cavalier King Charles Spaniel, the tests for episodic falling (EF) and for dry eye curly coat syndrome (CC/DE). In both breeds, however, the health problems people know most are not settled by a DNA test.

DM is a progressive deterioration of the spinal cord that starts in the hind legs, generally between 7 and 14 years of age. The Royal Kennel Club calls it a risk test: having two copies raises the likelihood but does not guarantee the dog will become ill. The Bernese club in the United States includes it among its minimum tests, together with hips, elbows, eyes and heart, and leaves a risk test for histiocytic sarcoma as optional.

In the Cavalier, a 2012 study identified the two mutations, both recessive. Episodic falling consists of episodes of muscle stiffness after exercise or excitement, which begin between three and seven months of age. Dry eye curly coat syndrome is noticeable from birth. The heart and syringomyelia are a different matter: see the Cavalier health guide.

Which tests do the parents of a Maltipoo or a Cockapoo need?

Those of their parent breeds. A cross has no tests of its own: it inherits those of the Poodle and those of the Maltese or the Cocker Spaniel. The one that comes up most is PRA-prcd, which US breed clubs recommend for the Toy and Miniature Poodle and for the English Cocker Spaniel.

Crossing two breeds does not cancel out a recessive disease that both share. If a Poodle that carries PRA-prcd is mated to a Cocker that carries it, an affected Cockapoo can be born, just as in a pure breed. What protects the puppies is testing the parents, not the cross.

What does a DNA test not tell you?

It does not tell you the dog is healthy: it tells you the dog does not have the mutations that were looked for. Many inherited diseases do not depend on a single known mutation, and for those no swab will do. The FCI strategy asks breeders to give them the same weight as the diseases that do have a test.

• Hip and elbow dysplasia is assessed with X-rays: we explain it in hip and elbow dysplasia in dogs.
• Congenital deafness is detected with the BAER test.
• Heart disease and many eye diseases need an exam by a specialist, repeated over time.