Congenital myasthenic syndrome (CMS) causes muscle weakness in Devon Rex and Sphynx cats. Clinical signs become evident at three to 23 weeks of age and usually progress slowly or remain static. Moderately to severely affected cats show evidence of more generalised muscle weakness, particularly following exertion, stress or excitement. Affected cats frequently adopt a characteristic 'chipmunk' position, usually with their front legs resting on a convenient object.
The mutation responsible for CMS has recently been discovered by researchers from the Universities of Missouri, California - Davis, California - San Diego, Sydney and Milan. The genetic disease is recessive, meaning that affected cats have two copies of the mutation. Cats with one copy of the mutation (carriers) are not affected, but can pass the mutation to their offspring.