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
Severe Combined Immunodeficiency
Severe Combined Immunodeficiency Disease (SCID) is a condition in which affected foals are unable to mount an effective immune response after infection and are unable to recover from infections that unaffected foals would easily resist. The disease is universally fatal in horses, usually within 4-6 months of life.
West Nile Virus Symptom Susceptibility / Risk
West Nile Virus (WNV) is a mosquito-borne virus that can infect multiple types of mammals, including horses. Infection can lead to a series of severe symptoms, most commonly encephalitis – acute inflammation of the brain. Severe neurological symptoms develop in ~8% of exposed horses, and once symptoms manifest, the fatality rate ranges from 20-40% and is higher in older horses.