Congenital myasthenic syndrome (CMS)
Congenital myasthenic syndrome (CMS) causes muscle weakness in Devon Rex and Sphynx cats. Affected cats show ventroflexion of the head and neck, head bobbing, scapulae protrusion and generalized muscle weakness and fatigability. Signs become evident at 3 to 23 weeks of age and usually progress slowly or remain static. Moderately to severely affected cats show evidence of more generalized muscle weakness, particularly following exertion, stress or excitement. Typically they have a high-stepping forelimb gait, head bobbing and progressive dorsal protrusion of the scapulae. Affected cats tire easily with exercise, with progressive shortening of the stride and superimposed tremor. Eventually they collapse in sternal recumbency, typically with the head coming to rest on, or to one side of, their front paws. Affected cats frequently adopt a characteristic 'chipmunk' position, usually with their front legs resting on a convenient object.
This illness requires a lot of care from the owner. Due to the inability to keep the head upright, feeding has to be supervised to make sure the cat can eat, but also to help prevent “inhalation” of the food (in the airways). The latter situation can be the main cause of pneumonia, often resulting in death or the need to euthanize the cat.
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 on to their offspring.
History
Soon after the Devon Rex was established, affected cats were found in all the countries where Devon Rex were bred. Before the arrival of the dna-test, the only way to pinpoint carriers, was through test-breeding. A lot of carriers were taken out of breeding plans, but as the disease is inherited in a recessive fashion, the gene remained afloat in the Devon Rex gene pool. Sphynx cats run a similar risk of getting the disease, because Devon Rex cats were used as outcross partners from the start of that breed. The gene responsible for the Drx curls, is recessive to the gene that causes hairlessness in the Sphynx, resulting in hairless kittens when mating a Devon Rex to a Sphynx. An outcross of the Sphynx with any other breed of cat, will bring forth coated kittens.
The mutation responsible for CMS has been discovered in 2015 by Marie Abitbol, Alfort School of Veterinary Medicine in Maisons-Alfort, France. A dna test followed soon after. Consequently the Universities of Missouri, California - Davis, California - San Diego, Sydney and Milan also developed a dna test.
Unfortunately, a lot of newer breeders of both the Devon Rex and the Sphynx are not aware of the risks of passing on CMS. Since the genes is inherited in a recessive mode, the genes can still be afloat in the gene pool of both breeds. In recent years some cases of DRX myopathy have surfaced in France. Breeders that have tested their breeding animals have come across carriers of the gene.
With GCCF In the United Kingdom, the test was made compulsory for breeding with Devon Rex and Sphynx soon after its discovery. More info on the history of the dna-test can be found here:
http://www.devonrex-ownersclub.co.uk/uploads/1/0/2/5/10250122/genetic_testing_for_spasticity.pdf
The Devon Rex owners club has kindly given permission to us to use the majority of the CMS-texts used on their website. Many thanks to Jen Pinches for correcting and editing the Pawpeds texts on CMS.