Greyhound Polyneuropathy (GHPN) is a disorder that belongs to a wider group of disorders knows as polyneuropathies. Inherited neuropathies until now have been recognized in 22 dog breeds, including Great Dane, Rottweiler, Dalmatian, Alaskan Malamute, Leonberger, German Shepherd, Italian Spinoni, Bouvier der Flandres, Border Collie etc. Canine polyneuropathies share many similarities with the Charcot-Marie-Tooth (CMT) group of diseases in humans. Charcot-Marie-Tooth is clinically characterized by muscle weakness and sensory loss. Polyneuropathy in literal translation means “many abnormalities of the nervous system”. The Greyhound breed before was primarily used as a racing dog, until 1960’s, when the breed was separated into show dogs and racing dogs. Researchers confirmed high inbreeding rate between Greyhound show dogs and revealed that all polyneuropathy affected dogs (GHPN) were related to a single popular sire born in 1968.
Greyhound Polyneuropathy (GHPN) is a neurodegenerative disorder with juvenile age of onset. Clinical signs appear between three to nine months of age. Owners of affected dogs already in early stages notice exercise intolerance and difficulties during walking, such as high stepping gait and bunny hopping. The gait appears as moderately to markedly ataxic, depending on the stage of disease, and appeared short-strided. After exercise shaking and collapse appears. As the disorder progresses, severe muscle atrophy, ataxia and dysphonia (voice disorders) develop. Reduction in muscle tone varies from moderately to severely, and lack of resistance to passive joint movement in either direction is present. Myotatic reflexes are reduced or absent. In terminal stages of the disorder cranial nerve function becomes affected. No behavioral changes have been reported, and affected dogs appear as alert, bright, and responsive. Neurological symptoms are delayed reactions, hyporeflexia, distal limb muscle atrophy, and inspiratory stridor. Motor and sensory nerve conductions become reduced.
Pathological findings show mild to marked reduction in myelinated nerve fiber density as well as hyperplasia of the axon-Schwann cell-network in about 10% of large myelinated fibers. Neurogenic atrophy was present within skeletal muscles, which varied in its severity between affected dogs.
After appearance of the clinical signs, affected dogs usually do not survive longer than ten months and commonly euthanasia is required due to humane reasons.
Greyhound Polyneuropathy (GHPN) is caused by a deletion in the NDRG1 gene. The prevalence of the mutation is high among show dog population of greyhounds, where 25% of the tested dogs revealed as carriers.
GHPN is inherited in an autosomal recessive pattern. Healthy parents of an affected puppy are obligate heterozygotes, and therefore carry one mutant allele. Heterozygotes have no symptoms. Dogs homozygous for the mutation will display the symptoms of the polyneuropathy. At conception, each cub has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.