Acral mutilation syndrome (AMS)

Acral Mutilation Syndrome is a neurodegenerative disease in dogs that belongs to the group of disorders known as Hereditary Sensory Autonomic Neuropathies. The disorder causes insensitivity to pain and temperature and progressive self-mutilation of the distal extremities.

This syndrome is known to affect several dog breeds, including French Longhaired Spaniel, English Springer Spaniel, English Pointer and German Shorthaired Pointer.

The disease is characterized by a sensory neuropathy in the limbs. The clinical symptoms include sudden intense licking, biting and severe self-mutilation of the feet (which can lead to auto-amputation of a limp part). The wounds are a common source of infection of different origin.  Swollen reddened spots and swelling, ulcers, abscesses, painless fractures and loss of claws occur on the affected limb parts.  Age of the symptoms onset varies from 3 to 12 months of age, mainly about the 4th month. The affected puppies are smaller than their healthy littermates. The dogs suffering from AMS do not feel any pain and can walk relatively normally on their severely mutilated feet without evidence of pain, lameness or ataxia.

The Acral Mutilation Syndrome is caused by a mutation within a regulatory region of gene for GDNF. GDNF is a neurotrophic factor derived from Glial cells that potently promotes the development of new neurons, the axon growth and the survival of adult neurons.  This mutation disturbs the expression of GDNF and leads to reduction of GDNF level, causing the decreased number of sensory neurons and their death. Proprioception, motor skills and spinal reflexes are not affected; the pathological process affects only primary sensory neurons.

AMS is inherited in an autosomal recessive pattern.  It means that the disorder will develop only in dogs that inherited the mutated allel from both parents (recessive homozygous for the mutation). Heterozygote is a dog that inherited the mutated allel only from one of its parents and shows no symptoms and is clinically healthy.  However, this dog is a carrier of the mutation and can pass it to its offsprings. When mating two heterozygous dogs, 25% of the pups will be healthy, 50% will be carriers of the mutation and 25% inherit the mutated allel from both parents and will develop AMS. Because of high risk of producing affected offspring, mating of two N/P animals (carriers) can not be recommended.

The genetic tests can reveal the genotype of the animal and can help prevent the unintentional spread of this disease.

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References:

Plassais , J., Lagoutte, L., Correard, S., Paradis, M., Guaguère, E., Hédan, B., Pommier, A., Botherel, N., Cadiergues, M.-C., Pilorge, P., Silversides, D., Bizot, M., Samuels, M., Arnan, C., Johnson, R., Hitte, C., Salbert, G., Méreau, A., Quignon, P., Derrien, T., André, C. : A Point Mutation in a lincRNA Upstream of GDNF Is Associated to a Canine Insensitivity to Pain: A Spontaneous Model for Human Sensory Neuropathies PLoS Genetics 12: e1006482, 2016.