Late Onset Ataxia (LOA) testing for the Jack Russell and Parson Russell terrier

Late onset ataxia or LOA for short is a hereditary health condition that can be found in some dogs of the Jack Russell and Parson Russell terrier breeds, which occurs due to a gene mutation that causes an uncoordinated gait when walking and moving around, and a general clumsiness and poor balance.

The condition is progressive, with the earliest symptoms usually becoming apparent when the affected dog is aged between six months and one year old. During the early stages of the condition’s development, the dog may just appear to be slightly stiff in their back legs, and have problems going up and down stairs, which can be confused with being just a normal part of the puppy learning process. Soon afterwards, the gait stiffness becomes more acute and the dog is apt to have problems jumping, as well as showing a distinctive “dancing” movement when standing in one place at times.

Progressing through the later stages of late onset ataxia, the condition can have a significant impact on the dog’s ability to walk and get up and down, as their incoordination and poor balance get worse. In some dogs, the condition will stabilise and not progress any further from the early stages, in which case it can be managed-but for other dogs, the condition will progress to its full extent, in which case euthanasia of the affected dog is usually indicated.

The condition occurs due to a malfunction of the spino-cerebellar region, which in turn, affects the muscle and nerves.

Late onset ataxia is not contagious and can only pass from dog to dog by means of heredity, which means that breeds that have been identified as at risk of the condition should be tested for the markers of the condition prior to breeding, to ensure the health of future generations.

The Kennel Club oversees a screening scheme for the condition in the Jack Russell and Parson Russell terrier breeds, and in this article, we will look at late onset ataxia in these breeds in more detail, including how the heredity of the condition works and how to get your dog tested. Read on to learn more.

More about late onset ataxia

As mentioned above, late onset ataxia progresses at different rates and to different extents in affected dogs, and for some dogs, the condition’s progression stalls at the early stages and will not have a significant negative impact on the dog’s quality of life.

However, for other dogs their quality of life, movement and ability to live a full and happy life become severely compromised, to the point that the only kind decision is euthanasia for the affected dog, to prevent further suffering. Generally, this occurs before the dog reaches the age of two.

Late onset ataxia is characterised by worsening incoordination and loss of balance, which can make everyday tasks and moving difficult. There is no treatment for this condition and affected dogs are often put to sleep around 2 years after onset.

What sort of dogs are at risk of the condition?

Late onset ataxia has been identified as present to a noticeable degree in the Jack Russell and Parson Russell dog breeds in the UK, to the extent that pre-breeding health screening is advisable in order to protect the health of future generations of dogs.

Cross breed dogs with one Jack Russell or Parson Russell parent may inherit the faulty gene that forms the marker for the condition from that side of their blood line, but unless they inherit a copy of the gene from both sides of their ancestry, they will not be affected (but may become a carrier).

However, crossing a Jack Russell with a Parson Russell terrier comes accompanied by the same risks of heredity from both sides as breeding a pedigree of either breed with one of the same breed does.

How does the heredity of the condition work?

The CAP1 gene is the gene responsible for late onset ataxia when the gene mutates, and this mutated gene passes from dog to dog by means of autosomal recessive heredity. Dogs may be either clear of the condition, affected by it, or a carrier for it without being affected themselves.

The mode of inheritance of late onset ataxia in dogs is as follows:

• Two clear dogs will have clear puppies.
• Two affected dogs will have affected puppies.
• Two carriers will produce a mixture of 50% carriers, 25% affected and 25% clear.
• A clear dog and a carrier will have 50% clear and 50% carriers.
• A clear dog and an affected dog will have a litter of carriers.
• A carrier and an affected dog will have 50% carriers and 50% affected.

How can you get your dog tested?

To find out your dog’s status and so, make an informed decision about breeding from them, you just need to ask your vet to take a DNA sample from your dog, and then send it off to one of The Kennel Club’s approved laboratories for testing.