Myelin is a mixture of proteins and phospholipids forming a whitish insulating sheath around many nerve fibers that protect nerve from outside influence and aid in increasing the speed at which impulses are conducted. The myelin sheath is a layer of fatty cells that covers each nerve in the body, including those in the brain and central nervous system.
Hypomyelination is a condition which is characterized by insufficient production of myelin. It is a congenital condition that affects the central nervous system (CNS), with related tremors that are most apparent when a dog is active.
CNS hypomyelination is prevalent in some breeds including Welsh springer spaniels, Samoyeds, chow chows, weimaraners, Bernese mountain dogs, and dalmatians. Male puppies in Samoyeds and springer spaniels are at a higher risk, showing symptoms within days of the birth while female dogs mostly remain asymptomatic carriers of the disease. There are no gender specific differences in other breeds.
Common signs and symptoms associated with this condition include
Central nervous system:
Clinical signs appear within days of birth
Body tremors that worsen with activity and decline during rest
Symptoms generally improve by one year of age in most breeds, with the exception of springer spaniels and Samoyeds, which are affected for life
Peripheral Nervous System:
Clinical signs appear at 5–7 weeks of age
Incoordination of the rear limbs (ataxia)
Hyporeflexia (below normal or absent reflexes)
Symptoms do not resolve with age