Hyperkalemic Periodic Paralysis, HYPP

 

Gene: SNC4A

Transmission: Autosomal dominant, variable expression

For an autosomal dominant genetic disease, an animal must have at least one copy of the mutation in question to be at risk of developing the disease.  Animals with two copies of the mutation generally have more severe symptoms and an earlier onset of the disease than animals with just one copy of the mutation.  One or both of the parents of an animal with the mutation has one or two copies of the mutation.  Animals that have one or two copies of the mutation can pass the mutation on to future generations.

Mutation: Substitution, SCN4A gene; c.4206, C>G, p.(F1416L), exon 25

Medical system: Muscular

Breed: Quarter Horse, American Paint

Age of onset of symptoms: Heat, cold, exercise, general anesthesia

Hyperkalemic Periodic Paralysis (HYPP) is a genetic disorder affecting the Quarter Horse.  HYPP is caused by an increase in potassium in the blood (hyperkalemia) due to a malfunction of the transmembrane channel of Na⁺ in the muscles.  Horses with HYPP show symptoms such as muscle tremors followed by paralysis, prolapse of the third eyelid, general weakness and abnormal neighing. There is no fever or pain.  In extreme cases, muscle paralysis can lead to death.  After an episode of HYPP, the horse appears normal.  The episodes are precipitated by heat, cold, exercise, a diet with excess potassium, general anesthesia and they can occur spontaneously.  The severity of attacks varies between horses and also between attacks for the same animal.  Horses with HYPP can usually be treated to reduce symptoms, depending on the stage of the disease.  Most horses affected by HYPP are heterozygous, with one good copy and one mutated copy of the gene that is involved.

 

References:

Labgenvet blog

OMIA link: [0785-9796]

Aleman M, Scalco, R, Malvick J, et al. (2022) Prevalence of genetic mutations in horses with muscle disease from a neuromuscular disease laboratory. J Equine Vet Sci 118:104129.  [pubmed/36150530]

Brooks SA. (2021) Genomics in the horse industry: Discovering new questions at every turn. J Equine Vet Sci 100:103456. [pubmed/34030792]

Tryon RC, Penedo MC, McCue ME, et al. (2009) Evaluation of allele frequencies of inherited disease genes in subgroups of American Quarter Horses. J Am Vet Med Assoc. 1;234(1):120-125. [pubmed/19119976]

Meyer TS, Fedde MR, Cox JH, Erickson HH. (1999) Hyperkalaemic periodic paralysis in horses: a review [Review] Equine Veterinary Journal 31:362-367. [pubmed/10505950]

Naylor JM, Nickel DD, Trimino G, et al. (1999) Hyperkalaemic periodic paralysis in homozygous and heterozygous horses: a co-dominant genetic condition Equine Veterinary Journal 31:153-159. [pubmed/10213428]

Rudolph JA, Spier SJ, Byrns G, et al. (1992) Periodic paralysis in quarter horses: a sodium channel mutation disseminated by selective breeding. Nat Genet. 2(2) : 144-147. [pubmed/1338908]