Spongiform Leukoencephalomyelopathy (SLEM) is a hereditary disease of Border Terriers, previously known as shaking puppy syndrome. When puppies begin to stand and attempt to walk, they show an uncontrollable shaking of their hind limbs. As the puppies grow, the shaking affects the entire body and their coordination is poor. Most pups are euthanized due to a poor quality of life, but there are reports of dogs improving with intensive nursing care.
Shaking puppy syndrome has been observed in a number of different breeds. However, SLEM in the Border terrier is genetically distinct and, as far as we know, not found in any other breed.
Research into the genetic basic of this disease is in the final stages at the Kennel Club Genetic Centre. Therefore the underlying variant that form the basis of our test has not yet been published. All evidence to date, including research and previous testing results, suggests that the variant we test is associated with SLEM.
The variant that we think causes SLEM in the Border terrier is recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop SLEM during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop SLEM as a result of the mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop SLEM 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 SLEM 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 SLEM, 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.