This is an uncommon condition that causes gait abnormalities (e.

g.

bunny hopping) in puppies.

Muscles become enlarged (hypertrophied), and this is especially noticeable in the shoulder and thigh areas.

The tongue is enlarged and may protrude from the mouth.

There may be a stiff gait, especially in the hindlimbs, and affected animals may have difficulty getting to their feet and balancing.

Signs are usually evident at a young age.

This condition occurs in several breeds, most commonly in the chow chow and miniature Schnauzer.

In the miniature Schnauzer the condition is autosomal recessive and the mutation has been characterised, with a DNA test available.

In people recessive and dominant forms are seen.

The condition occurs due to a mutation in a gene that controls the muscle membrane ion channels (i.

e.

the gates that control flow of sodium and chloride across the muscle cell wall).

This abnormality delays the relaxation of the muscle fibre so that in effect the muscles are overly tensed, leading to the increase in their size and decreased muscle control that is seen.

Diagnosis is made by electromyography (studies of the passage of electrical impulses through the muscle tissue) and muscle biopsy.

The condition can be treated (not always successfully) with membrane stabilising drugs (that act to block the sodium or chloride channels) but cannot be cured.