Neuronal ceroid lipofuscinosis (NCL) is a progressive neurodegenerative disease found in dogs, humans, and other animals. It is characterised by the widespread accumulation of lipopigment in neurovisceral tissue and clinical signs of neurological disease. Onset of clinical signs of this form of NCL in Border collies can be from 15 months, but the age of onset of the disease is variable. Affected dogs develop ataxia and psychological abnormalities, including agitations, aggression, hallucinations, and hyperactivity. The disease is progressive and most dogs will lose the ability to coordinate functions such as house training, walking and eating. There is no treatment or cure, and as a result, affected dogs seldom live beyond 28 months of age.
The single nucleotide substitution in the gene called CLN5 that causes Neuronal Ceroid Lipofuscinosis in Border Collie is autosomal recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop Neuronal Ceroid Lipofuscinosis during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop Neuronal Ceroid Lipofuscinosis as a result of the CLN5 mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop Neuronal Ceroid Lipofuscinosis 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 CLN5 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 Neuronal Ceroid Lipofuscinosis, 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.