Sensory Neuropathy (SN)

Description

Sensory Neuropathy (SN) is a progressive neurological disorder in Border Collies. It is caused primarily by the degeneration of sensory nerve cells, although some motor nerve cells can also be affected.  Symptoms of the disorder generally appear between 2 and 7 months of age.

Clinical signs include difficulty walking due to abnormal extended limbs. Hind limbs are generally more affected than the front limbs.  Additional symptoms include the knuckling of paws, muscle degradation, urinary incontinence, and regurgitation. These signs are typically seen in later stages of the disease.  Affected animals often develop a tingling or numbing sensation, which drives them to lick or chew on their limbs and feet excessively. This results in large wounds caused by self-mutilating behavior.  The prognosis is poor. Due to the severely poor quality of life, dogs that are diagnosed with SN are often euthanized within 18 months.

It has been discovered in Border Collies that an inversion in the FAM134B gene (a gene that codes for proteins that protect nerve cells) is the genetic cause for a genetically recessive form of the disease. Genetically recessive diseases are diseases that can be passed from either parent and require two copies of the gene to show symptoms. This means that a dog must have 2 copies of the mutated FAM134B gene (one coming from each parent) in order for the dog to experience symptoms. 

Dogs with one copy of the mutated gene are considered carriers and will not be affected. If breeding to another carrier, however, there is a 25% chance per puppy that they will develop SN symptoms and will have to be euthanized.