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Articles on Rex Health:Blood Types: Myopathy in Devon Rexes: White Rex & Deafness: Appeal for help: Do you have a cat allergy?: |
Devon Rex Hereditary Myopathyby Susan Little DVMDiplomate ABVP (Feline Practice). Bytown Cat Hospital, Ottawa, Ontario, Canada Ever since the mid-1970s, a neuromuscular disease was known to exist in the
Devon Rex breed. The disease first appeared in Britain, Australia and New
Zealand, then other parts of the world, including Canada and the United States.
Despite the length of time this disease has been known, there are few reports or
articles about it in the veterinary literature. The disease was christened "spasticity"
by the first breeders that encountered it, but this has proven to be an
incorrect term. Research has shown that the disease is most likely a muscular
dystrophy.
Clinical signs may seem to wax and wane. Once signs are noticed, they tend to progress at a variable rate until about six to nine months of age, when they appear to stabilize or progress only very slowly. As the affected cat matures, the signs may even seem to improve a bit, usually as the cat develops adaptive behaviours. How is it inherited? Roy Robinson conducted a detailed pedigree analysis and examined the results of 20 test matings in 1992. He concluded that the disease is inherited in an autosomal recessive fashion. However, the gene involved has not yet been identified. How is hereditary myopathy diagnosed? The diagnosis of hereditary myopathy in Devon Rex cats requires a combination of the distinctive clinical signs and the results of diagnostic tests. Since there are various other myopathies known in the cat (secondary hypokalemic polymyopathy, inherited hypokalemic polymyopathy, X-linked muscular dystrophy, nemaline myopathy, etc.), laboratory tests and clinical signs are useful to rule out these other diseases. Although rarely warranted, congenital myasthenia gravis can be ruled out if suspected by response to intravenous edrophonium (Tensilon®). Physical examination findings: Clinical signs (as outlined above) are suggestive of hereditary myopathy, and no neurological abnormalities are found. Routine blood testing: Results of routine blood cell counts and serum chemistries are typically normal. This helps to rule out the hypokalemic polymyopathies (associated with low serum potassium levels) and both X-linked muscular dystrophy and nemaline myopathy (both associated with high blood levels of creatine kinase). Muscle biopsy: Biopsy specimens should be obtained from muscle groups that appear to be most affected, such as the biceps brachii, triceps brachii, or biceps femoris. Biopsies should be obtained under general anesthesia or at necropsy. Fresh unfixed samples (i.e. not preserved in formalin) should be submitted to a laboratory and pathologist with experience in diagnosing muscular dystrophies. The laboratory should be consulted in advance about guidelines for sample submission. Muscle biopsy changes typical of hereditary myopathy include features typical of muscular dystrophies, such as increased variability in muscle fibre size, hypertrophy and atrophy of fibres, rounded and split fibres, internal nucleation, etc. Features associated with other known myopathies, such as central cores, nemaline rods and increased stores of glycogen or lipid are not found in this disease. Is there any treatment for this disease? Unfortunately, there is no known treatment. Upper airway obstruction and death by choking or by aspiration pneumonia are the most common threats to the life of affected cats. Patients that have difficulty eating should be hand-fed or fed from a raised dish. To avoid accidental choking, severely affected cats should never have free access to food. Particular attention should be paid to preventative health care, since any concurrent illness can make signs of the disease worsen. Patients with moderate to severe weakness should live in an environment where they do not have to travel far or exert themselves to reach food, water and litter box. Overexertion, such as during play, should be avoided. Exposure to cold temperatures should also be avoided, since it appears to worsen signs. What do I do about my breeding program if I identify an affected cat? Obviously, affected cats should not be bred. Since it is suspected that a recessive gene causes this disease, both parents of an affected cat are carriers. It would be wise to remove such parents from a breeding program where possible. If a screening test should become available, it would be possible to screen kittens from an affected pair and keep an unaffected kitten to replace the parents. However, no such test is available, so it is not possible at this time to detect carrier cats except through test matings. Material for this article was drawn from the following sources: Malik R, Mepstead K, Yang F, Harper C. Hereditary myopathy of Devon rex cats. Journal of Small Animal Practice 34:539-546, 1993 Robinson R. "Spasticity" in the Devon rex cat. Veterinary Record 130:302, 1992 Winand NJ. Inherited myopathy of Devon Rex cats. Feline Health Topics for Veterinarians 9(1): 1, 1994 Dr Susan Little is currently running studies on kitten health and mortality,
in both Devon Rex and Sphynx. For more information, and to register to
participate in these studies, visit:
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