Part of the official UK Kennel Club testing scheme in Border Collie
Trapped Neutrophil Syndrome is an immune defect known as neutropenia (abnormally low levels of white blood cells). White blood cells are produced by the bone marrow, but they are not released into the bloodstream. Affected dogs are therefore susceptible to illness and repeated infections.
Some affected puppies are smaller than their littermates and suffer from chronic infections and failure to thrive from as early as 6 weeks. For others the first signs of TNS may only be an adverse reaction to immunisation. There is no cure for TNS.
The 4 bp deletion in the gene called VPS13B that causes Trapped Neutrophil Syndrome in Border Collie is Autosomal recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop Trapped Neutrophil Syndrome during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop Trapped Neutrophil Syndrome as a result of the VPS13B mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop Trapped Neutrophil Syndrome 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 VPS13B 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 Trapped Neutrophil Syndrome, 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.