'Cerebellar hypoplasia' is the term used to describe the condition in which the portion of the brain called the cerebellum either fails to fully develop or begins to degenerate shortly after birth. The cause may be genetic, related to an infection of the puppy while it was still in the uterus, or the cause is often unknown.
The genetic or inherited form is more common in certain breeds of dogs including Irish Setters, Airedales, and Chows.
Herpesvirus infection in dogs has been associated with the development of cerebellar hypoplasia.
Regardless of its cause, the condition is first recognized shortly after two weeks of age. The head will tremor and 'bob,' especially when the puppy attempts a function. As an example, while it reaches for a nipple to nurse upon, the head will jerk towards the nipple in an exaggerated tremoring fashion. This type of movement is referred to as 'intention tremors.' In other words, when the puppy intends to do something it tremors. While at rest it does not tremor. The tremors may progress and become severe. This makes the puppy unable to develop normal eating and walking capabilities. Some dogs with nonprogressive disease may have mild intention tremors throughout life, but still lead happy lives. There is no treatment.