Myotonia (MYT)
Gene or Region: CLCN1
Reference Variant: A
Mutant Variant: C
Affected Breeds: New Forest Pony
Research Confidence: Moderate - Mutation was not found in 56 control horse of 13 different breeds, and mutations in the same gene result in myotonia in other species
Explanation of Results: MYT/MYT = homozygous for Myotonia, trait expressed MYT/n = heterozygous for Myotonia, carrier n/n = no variant detected
General Description for Myotonia
Myotonia is a rare disorder involving a slowed relaxation of muscles after contraction. The most well-known example of myotonia is “fainting goats,” a breed that is characterized by sudden rigidy and/or falling over when startled. In the single documented horse, this resulted in a protruding third eyelid when excited, as well as problems with muscle stiffness (and thus difficulty in rising and movement). This mutation is believed to be a more recent occurrence within the New Forest Pony breed.
Gene Information
_CLCN1 _is a voltage-dependent chloride channel involved in signaling in muscles. Mutations in this gene have been associated with myotonia is humans, dogs, and goats. This specific mutation described in the horse results in an amino acid change, which likely alters the function of the encoded protein.
References
Wijnberg ID et al., “A missense mutation in the skeletal muscle chloride channel 1 (CLCN1) as candidate causal mutation for congenital myotonia in a New Forest pony.” (2012) Neuromuscul Disord. 22: 361-7. PMID: 22197188
More Horse Health
Occipitoatlantoaxial Malformation 1
Occipitoatlantoaxial Malformation 1 (OAAM1) is an inherited developmental condition predominantly found in Arabian horses, characterized by abnormal development of the cervical vertebrae leading to compression of the upper cervical cord and subsequent neurological damage.
Polysaccharide Storage Myopathy
Polysaccharide Storage Myopathy (PSSM) is a glycogen storage disorder in which affected horses have chronic episodes of exertional rhabdomyolysis (“tying-up”). Acute symptoms are an unwillingness to move and muscle damage following exercise. Moderate symptoms can usually be managed through a low-sugar/starch diet and exercise.
Recurrent Laryngeal Neuropathy
Recurrent Laryngeal Neuropathy (RLN) is a disease that results in loss of the neurons that open the larynx, significantly affecting performance in Thoroughbreds and other sport horses. It is an important issue for horses in competitive events because the resultant paralysis of the larynx leads to obstruction of air flow during intense exercise, creating the abnormal inspiratory noise that gives RLN its common name: “roaring”.