Myotonia Congenita

What is Myotonia Congenita in dogs?

muscle diagramMyotonia Congenita is an inherited muscle disease with an autosomal recessive pattern of inheritance. Myotonia Congenita is also referred to as non-inflammatory myotonia to distinguish it from the inflammatory type. Myotonia Congenita arises from genetic defects in the ion channels of skeletal muscle cells in the affected dog causing reduced conductance. The reduced conductance results in a delayed response to the end of muscle activity in the body so the dog’s muscles take a lot longer than normal to return to a relaxed state. This gives way to difficulty moving normally and muscle hypertrophy (excessive growth of the muscles). Although Myotonia Congenita is thought of as a disease of the muscles, other parts of the body are also affected. There is no cure for Myotonia Congenita at this stage. There is a form of this disease that can be acquired without a genetic origin and experiment have shown that high exposure to certain herbicides can initiate the disease in laboratory animals.

Genetics of Myotonia Congenita in dogs

Myotonia Congenita has an autosomal recessive pattern of inheritance with the mutated form of the CLCN1 being responsible for the condition. The mutated form of the CLCN1 gene is recessive to the normal version of the gene, so if one of the dog’s copies of the gene is normal, it will cancel out the effects of the faulty gene. This is why dogs with one mutated copy are called carriers, dogs with two normal copies are called clear and those dogs with 2 mutated CLCN1 genes are affected dogs. The mutated form of the gene can be a simple point mutation in this case.

Severity of Myotonia Congenita in affected dogs

Myotonia Congenita is considered to have a medium to high level of severity as the condition does make life for the dog somewhat difficult, and may place the affected dog in danger when they cannot move appropriately to deal with the world around them. However, the condition is not thought to be painful for the affected dog but the reduced mobility is assumed to be frustrating. Dogs affected by Myotonia Congenita will usually have a normal lifespan for their breed.

What are the symptoms of Myotonia Congenita in affected dogs?

muscle fiber chevromistMyotonia Congenita affects the ion channels in muscle cells which are highly sensitive to other factors both in and outside the cells or body, so symptoms will naturally vary between affected individuals. The typical symptoms that have come to characterise Myotonia Congenita start when the puppy is starting to walk and include a stiff gait with slow and difficulty moving, falling over, a bunny hop gait, abnormal posture and an obvious enlargement of the muscles (particularly of the hind limbs). Other symptoms with variable severity between affected dogs include dental and jaw abnormalities as well as abnormal breathing, barking and swallowing.

Diagnosis of Myotonia Congenita in dogs

Diagnosis of Myotonia Congenita via biochemistry analysis of blood and urine can give clues as to the presence of the condition. Tapping on the tounge of a dog suspected of being affected by Myotonia Congenita and examining the amount of dimpling has been tried as a diagnosis method. The only reliable and definitive method of diagnosis of Myotonia Congenita is with a DNA Disease Screen.

Treatment of Myotonia Congenita in dogs

At the present time, there is no single course of treatment for dogs affected by Myotonia Congenita but a number of drugs to help compensate for the disrupted ion channels, muscular stiffness and regurgitation can be used to treat affected dogs. The treatment will vary between individuals depending on their symptoms and response to various drugs but so far there is no drug therapy to correct the characteristic gait of affected dogs.

References

Bhalerao DP, Rajpurohit Y, Vite CH, Giger U. (2002) Detection of a genetic mutation for myotonia congenita among Miniature Schnauzers and identification of a common carrier ancestor. Am J Vet Res. 63(10):1443-7

Gracis M, Keith D, Vite CH. (2000) Dental and craniofacial findings in eight miniature schnauzer dogs affected by myotonia congenita: preliminary results. J Vet Dent. 17(3) :119-27

Papponen, H.; Toppinen, T.; Baumann, P.; Myllylä, V.; Leisti, J.; Kuivaniemi, H.; Tromp, G.; Myllylä, R. (1999). “Founder mutations and the high prevalence of myotonia congenita in northern Finland”. Neurology 53 (2): 297–302

Rhodes TH, Vite CH, Giger U, Patterson DF, Fahlke C, George AL Jr. (1999)A missense mutation in canine C1C-1 causes recessive myotonia congenita in the dog. FEBS Lett.ers 456(1):54-8

Shores A et al (1986) Myotonia congenita in a Chow Chow pup. J Am Vet Med Assoc 188(5):532-533

Vite CH, Cozzi F, Rich M, Klide AK, Volk SW, Lombardo R. Myotonic myopathy in a miniature Schnauzer: case report and data suggesting abnormal chloride conductance across the muscle membrane. J Vet Intern Med. 1998 Sep-Oct;12(5):394-7

Vite CH, Melniczek J, Patterson D, Giger U. (1999) Congenital myotonic myopathy in the schnauzer (miniature): an autosomal recessive trait. Journal of Heredity. 90(5):578-80

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