Myotonia congenita

From Dog
Physical appearance of a dog with myotonia congenita, showing characteristic skeletal muscle hypertrophy[1]

Myotonia congenita is an autosomal-recessive genetic disease of dogs characterized by skeletal muscular hypertrophy.

Myotonia is caused by delayed skeletal muscle relaxation following activity as a result of poor skeletal muscle voltage-dependent chloride channel conductance. This electrochemical disorder originates from a missense mutation in the canine C1C-1 allele[2].

This disease has been reported in the Miniature Schnauzer, Chow Chow[3] and Jack Russell Terrier[4] and is characterized by a delay of relaxation of the muscles following a stimulus or after cessation of voluntary activity.

Affected dogs usually present with non-painful muscle spasms, stridor, dyspnea, dysphonia, stiff-stilted gait, bunny-hopping and collapse associated with exercise and activity.

In Schnauzers, there is also delayed dental eruption of both deciduous and permanent dentition, crowding and rotation of premolar and or incisor teeth and missing teeth[5]. A long narrow skull with a flattened zygomatic arch and greater mandibular body curvature were also consistent findings in the affected dogs.

Neurological examination, blood tests, muscle biopsy and histopathology are often unrewarding.

Diagnosis usually requires PCR-based DNA testing, which usually shows a mutation in the CIC-1 allele[6].

A differential diagnosis would include cerebellar abiotrophy.

References

  1. IVIS
  2. Rhodes TH et al (1999) A missense mutation in canine C1C-1 causes recessive myotonia congenita in the dog. FEBS Lett 456(1):54-58
  3. Shores A et al (1986) Myotonia congenita in a Chow Chow pup. J Am Vet Med Assoc 188(5):532-533
  4. Lobetti RG (2009) Myotonia congenita in a Jack Russell terrier. J S Afr Vet Assoc 80(2):106-107
  5. Gracis M et al (2000) Dental and craniofacial findings in eight miniature schnauzer dogs affected by myotonia congenita: preliminary results. J Vet Dent 17(3):119-127
  6. Bhalerao DP et al (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):1443-1447