hereditaryspinalmuscularatrophy

Canine Hereditary Spinal Muscular Atrophy

This disease manifest as weakness and atrophy of skeletal muscles. Some forms of this disease are inherited. The disease is inherited as an autosomal dominant characteristic and shows striking clinical and pathological features in common with human motor neuron disease but it is molecularly distinct from the human version of spinal muscular atrophy.

Hereditary Canine Spinal Muscular Atrophy (HCSMA) is a motor neuron disease that cause degeneration of motor neurons in the anterior (near the head) section of the spinal cord. Motor neurons are the nerve cells that convey impulses to the muscles to produce movement. This condition results in significant progressive muscularweakness and atrophy resulting in difficulty in supporting weight, reduced reflexes, abnormal gait, muscle tremors, and loss of muscle tone/mass (muscle atrophy). A subcategory of the condition called German Shepherd Focal Spinal Muscular Atrophy often seen in dogs of German Shepherd heritage is thought to involve a smaller area of motor neuron damage.

Once initial muscle weakness is observed, the condition generally becomes rapidly progressive. The condition is considered “accelerated” if initial weakness is noted prior to 1 month of age and progresses rapidly, “ intermediate” if initial weakness noted at 4‑6 months of age and progresses rapidly, and “chronic” if the initial weakness is noted in an older puppy and progresses slowly. Accelerated motor neuron disease generally results in paralysis before the age of six months, and intermediate motor neuron disease by 2-3 years of age. Dogs with the “chronic” form of motor neuron disease may live well into their adult lives. Similarly, the effects of focal spinal muscular atrophy often seen in breeds of German Shepherd heritage can be relatively mild and slow to progress. Additionally, unlike some other forms of motor neuron disease, the weakness or paralysis may be limited to the tail, hind end, or even just one limb.

Diagnosis is based on a thorough neurologic examination, the absence of abnormalities on routine diagnostic tests, and the progressive nature of the condition. Specific diagnostic tests might include testing the dogs reflexes, muscle biopsy, and electronic nerve conduction studies.

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Canine Hereditary Spinal Muscular Atrophy

related terms: inherited motor neuron diseases
http://www.upei.ca/cidd

<>What is spinal muscular atrophy?
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

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AD (autosomal dominant) Only 1 copy of the gene, which may be inherited from either parent, is required to produce the trait. The parent with the dominant trait will pass the affected gene to approximately half its offspring, and the trait will be apparent in both the parent and the affected progeny. These conditions are uncommon because, as long as it is of early onset (ie becomes apparent before breeding age is reached), the disorder can be readily eliminated by avoiding the breeding of affected individuals.

In many instances however, there is incomplete dominance. The trait may be dominant with variable expressivity, which means that if either parent is affected, all puppies have a susceptibility to the disorder but not all will be affected equally. Alternately, a dominant trait may have incomplete penetrance. If penetrance is 75% for example, only about 3 quarters of the pups who inherit the trait will express it.
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.

AR (Autosomal recessive) This is the most common mode of inheritance for genetic conditions in dogs. Progressive retinal atrophy (PRA), which causes blindness in many breeds, is such a trait. To be affected, the animal must inherit 2 copies of the gene (genotype pp), 1 from each parent. Dogs with the genotype PP (normal) or Pp (carrier) will be clinically normal but the carrier will pass the affected gene to approximately half the offspring. As long as carriers (Pp) are mated to normal animals (PP), the offspring will be unaffected but some will remain carriers. If 2 carriers are mated, some of the offspring (approximately 25%) will be affected.

How is spinal muscular atrophy 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.

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.

How is spinal muscular atrophy 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.

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.

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources
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.

This database is a joint initiative of the Sir James Dunn Animal Welfare Centre at the Atlantic Veterinary College, University of Prince Edward Island, and the Canadian Veterinary Medical Association.
Permission to reprint is granted by
Alice Crook, DVM Coordinator, Sir James Dunn Animal Welfare Centre
Atlantic Veterinary College University of Prince Edward Island

Lower Motor Neuron Disease in the Griffon Briquet Vend&en Dog