related terms: hypo-/dysmyelination, "shaking pup"
What is hypo-/dysmyelinogenesis?
Myelin is a fatty substance that coats nerve cells. It serves as an electrical insulator and speeds the conduction of nerve impulses. The formation of myelin begins mid-way through pregnancy and continues for a short period after birth.
In this disorder, there is a lack of ("hypo"), or abnormal ("dys") myelination, primarily in the spinal cord but also in parts of the brain. Most affected is the general proprioceptive system, which is important for the coordination of body movements and positioning.
The condition is most severe in the springer spaniel and samoyed. In other breeds, puppies often gradually improve, perhaps because of continued slow myelination of cells after birth.
How is hypo-/dysmyelinogenesis inherited?
The condition is an x-linked trait in the springer spaniel ("shaking pup") and possibly the samoyed. In other breeds it is believed to be autosomal recessive.
What breeds are affected by hypo-/dysmyelinogenesis?
This uncommon disorder occurs in the springer spaniel ("shaking pup"), chow chow, Weimaraner, Bernese mountain dog ("trembler"), and samoyed.
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. We have listed breeds for which there is a consensus among those investigating in this field and among veterinary practitioners, that the condition is significant in this breed.
What does hypo-/dysmyelinogenesis mean to your dog & you?
Because the proprioceptive system is most affected, pups with this condition have problems with balance, coordination, and positioning. They have a wide-based stance, and appear clumsy (but without weakness). Pups may have what is described as a rocking horse gait. There are pronounced tremors of the head and legs, which are stronger when the pup is excited or moves, and subside at rest or during sleep. Affected pups are normally alert and responsive to their surroundings.
Signs are first noticed after birth or when the pups first walks. With the exception of the springer spaniel and samoyed, these signs do not worsen but instead improve gradually over several weeks or months, often to normalcy by 1 year.
Because the trait is sex-linked in the springer spaniel, males are most severely affected. By about 2 weeks of age, male pups develop a severe tremor of body, head and legs that decreases during rest and worsens with excitement. They are unable to stand, walk, or eat and generally do not survive unless intensively hand-reared. Females will be carriers of the trait and may show mild signs as puppies that disappear by 4 to 6 weeks of age.
How is hypo-/dysmyelinogenesis diagnosed?
There are other conditions, primarily affecting the cerebellum, that cause similar signs in newborn puppies. Your veterinarian will do tests to rule out other possible causes.
For the veterinarian: Primarily proprioceptive fibers are affected, so clinical signs resemble cerebellar disease. In neonates this condition is easily confused with cerebellar hypoplasia. Diagnosis is based on the clinical signs, gradual improvement (except in the springer spaniel and samoyed), and lack of significant findings on other diagnostic tests.
How is hypo-/dysmyelinogenesis treated?
There is no treatment, but affected puppies tend to improve over time, often to complete recovery by 1 year of age. Samoyeds and male springer spaniels show little if any improvement.
The mother of any affected springer spaniel pup is a carrier and should not be used again for breeding. Breeding of his sisters should also be avoided as they have a 1 in 2 chance of being a carrier, and passing this severe disorder to any male offspring.
In other breeds, affected animals (even if recovered to normalcy), their parents (carriers of the trait) and siblings (suspect carriers) should not be bred.
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.
Cuddon, P.A., Duncan, I.D. 1992. The canine myelin mutants - clinical, electrophysiological, MRI, and pathological studies. ACVIM- Proceedings of the 10th Annual Vet. Med. Forum. pp 757-759.
Ackerman, L. 1999. The Genetic Condition: A Guide to Health Problems in Purebred Dogs. pp 134-135. AAHA Press. Lakewood, Colorado.
Copyright © 1998 Canine Inherited Disorders Database. All rights reserved.
Revised: October 30, 2001.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.