Spinal muscular atrophy/motor neuron diseases

What is ... ?: 

  The term spinal muscular atrophy is applied to most of the inherited motor neuron diseases in humans that affect mainly (although not exclusively) motor neurons. Motor neurons are the nerve cells that convey impulses to the muscles to produce movement. The syndromes vary between breeds (see below) but in general, degeneration of these neurons causes progressive weakness with difficulty in supporting weight, reduced reflexes, abnormal gait, and a loss of muscle mass (muscle atrophy).


The disorder in the Brittany spaniel is uncommon and the rest of these disorders are very rare.

Abnormality Breeds affected (RARE) Inheritance Clinical features
Spinal muscular atrophy Brittany spaniel AD signs appear by 3 to 4 months (homozygotes), and are rapidly progressive; or not until 2 to 3 years (heterozygotes); initial weakness in hind end progresses to involve all 4 limbs
Focal spinal muscular atrophy German shepherd unknown signs by 1 to 2 months; weakness in the front legs
Hereditary progressive spinal muscular atrophy English pointer AR weakness in hind limbs by 6 months; progresses to forelimbs
Motor neuron disease Rottweiler unknown signs by 1 to 2 months; weakness in all limbs +/- abnormalities in swallowing causing regurgitation (megaesophagus)
Multisystemic chromatolytic neuronal degeneration Cairn terrier unknown signs by 4 to 7 months; generalized weakness, poor coordination, head tremor

For many breeds and many disorders, the studies to determine the mode of inheritance or the frequency in the breed have not been carried out, or are inconclusive.

How is ... diagnosed?: 

 Diagnosis is based on a thorough neurologic examination, the absence of abnormalities on routine diagnostic tests, and the progressive nature of these conditions. Specific diagnostic tests include muscle biopsy and electronic testing of nerve conduction potentials (an electromyogram) of affected muscles.

How is ... treated?: 

 There is no treatment. These conditions are slowly or rapidly progressive, with the exception of German shepherd focal spinal muscular atrophy where the effects may be relatively mild.

For the veterinarian: 

The lower motor neuron signs with these disorders may be confused with canine protozoan radiculomyelitis. Electromyography typically shows spontaneous denervation potentials. Muscle atrophy is evident on muscle biopsy.

Breeding advice: 

 Affected dogs should not be bred. Breeding of parents and siblings (suspect carriers) should be avoided as well, so as not to perpetuate these serious and fortunately rare disorders. In family lines of Brittany spaniels where this disorder has occurred, dogs should not be bred until at least 3 years of age to ensure that any carriers are recognized.



 Ackerman, L. 1999. The Genetic Condition: A Guide to Health Problems in Purebred Dogs. pp 145-146. AAHA Press. Lakewood, Colorado.

 Cummings, J.F., deLahunta, A. 1995. Canine neurodegenerative diseases involving motor neurons. In J.D. Bonaguara and R.W. Kirk (eds.) Kirk's Current Veterinary Therapy XII Small Animal Practice. pp. 1132-1136. W.B.Saunders Co., Toronto.

Cork, L.A. 1992. Canine ventral horn cell disease. In J.D. Bonaguara and R.W. Kirk (eds.) Kirk's Current Veterinary Therapy XI Small Animal Practice. pp. 1031-1034. W.B. Saunders Co., Toronto. - This reference contains information on hereditary canine spinal muscular atrophy in Brittany spaniels.

What breeds are affected by ... ?