Myasthenic syndromes are hereditary diseases caused by defective signal transmission in the neuromuscular junction. In the Sphynx and Devon Rex breeds, the disease is caused by the deficiency of alpha-dystroglycan expression in the neuromuscular synapses which results in reduced activity of acetylcholinesterase. Affected cats present with progressive muscular signs such as fatigue, reduced activity, generalized skeletal muscle weakness, and muscle tremors after exercise. Functional deficiency in the limb-girdle and axial musculature can lead to gait abnormalities, protrusion of the scapulae, and ventroflexion of the head and neck. Affected cats may also present with megaesophagus and can have difficulty swallowing which may lead to asphyxiation or aspiration pneumonia. Clinical signs are typically visible in kittens before five months of age and may be evident in some individuals as young as three weeks of age. Severity of clinical signs can vary and, while the disorder is slowly progressive, occasional cases do become static.

Upon initial observation of clinical signs, affected cats should be closely monitored to assess welfare and devise a supportive care treatment plan. Difficulty swallowing is a significant concern and elevation of food and water bowls may help to reduce the risk of asphyxiation or aspiration pneumonia. Affected cats experiencing progressive difficulties with swallowing are often euthanized for welfare reasons.

There are many responsibilities to consider when breeding cats. Regardless of test results it is important that your cat is in good general health and that you are in a position to care for the kittens if new responsible owners are not found. For first time or novice breeders, advice can be found at most cat registry websites.

This disease is autosomal recessive meaning that two copies of the mutation are needed for disease signs to be shown. A carrier cat with one copy of the CMS mutation can be safely bred with a clear cat with no copies of the CMS mutation. About half of the kittens will have one copy (carriers) and half will have no copies of the CMS mutation. Kittens in a litter which is expected to contain carriers should be tested prior to breeding. Carrier to carrier matings are not advised as the resulting litter may contain affected kittens. Please note: It is possible that disease signs similar to the ones caused by the CMS mutation could develop due to a different genetic or clinical cause.