Exercise induced paroxysmal movement disorder affects young Weimaraner puppies (younger than 8 months of age). Affected dogs display episodic gait abnormalities characterised by increased muscle tone (spasticity), ataxia (poor coordination) and hypermetria (over reaching movements). The episodes, which can lead to collapse, last 5-15 minutes and are triggered by excitement and/or exercise. In between the episodes the dogs appear normal.
The frameshift in the gene called TNR that causes Exercise induced paroxysmal movement disorder in Weimaraner is autosomal recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop Paroxysmal movement disorder during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop Paroxysmal movement disorder as a result of the TNR mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop Paroxysmal movement disorder should be the breeder’s priority, with a reduction in mutation frequency within the whole breed being the secondary, longer-term target.
Carriers can be bred from safely, provided they are mated to a dog that has also been tested and is clear of the TNR mutation (i.e. carry no copies of the mutation). If a carrier is mated to a clear dog approximately half of the resulting puppies will also be carriers, so should be tested themselves prior to breeding. Breeding carriers to tested, clear dogs is safe, in terms of avoiding dogs affected with Exercise induced paroxysmal movement disorder, and will help to maintain the genetic diversity of a breed. It is therefore encouraged, particularly in the first few generations following the availability of a new genetic test, so that other desirable characteristics and traits can be preserved before the frequency of the disease mutation within the breed is gradually reduced.