Part of the official UK Kennel Club testing scheme in Leonberger
Canine leukoencephalomyelopathy (LEMP) is a juvenile-onset neurodegenerative disorder of the central nervous system white matter. Clinical signs first appear in young dogs, between one and three years of age. These signs include the inability to control bodily movements, inability to judge distance, generalized muscle weakness, hypermetria, and exaggerated spinal reflexes. Neuronal examination revealed myelin breakdown, followed by swelling of the axons. Due to the progressive derogative nature of the disorder, affected dogs are usually euthanized.
The single nucleotide substitution in the gene called NAPEPLD that causes Leukoencephalomyelopathy in Leonberger is Autosomal recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop Leukoencephalomyelopathy during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop Leukoencephalomyelopathy as a result of the NAPEPLD mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop Leukoencephalomyelopathy 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 NAPEPLD 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 Leukoencephalomyelopathy, 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.