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→ Temporary paralysis in Quarter Horses


  • General weakness
  • Periodic tremors and paralysis
  • Respiratory noise
  • Heavily muscled

General Information:

  • Varies in severity.
  • May be life-threatening when heart or lungs are affected by paralysis.
  • Symptoms may occur more frequently after changes in diet, stress or transportation.
  • Improper signalling between brain and muscles/organs.
  • Symptoms may be reduced with potassium-deficient diet (avoid Lucerne/Alfalfa in hay)
  • Can be traced back to the sire “Impressive”.

Inheritance: autosomal dominant

→ Horses with one or two copies of the variant (n/HYPP or HYPP/HYPP) are affected.

Possible Genotypes:

Genotype The horse is:
n/n normal. The horse has no copies of the genetic variant causitive for HYPP and therefore cannot pass it on to its offspring
n/HYPP affected (heterozygous). The horse is affected.  The genetic variant will be passed on to its offspring with a probability of 50%. These foals will be affected.
HYPP/HYPP affected (homozygous). The variant will be passed on to all of its offspring. All offspring will also be affected.



  • Affected animals (n/HYPP or HYPP/HYPP) should not be used for breeding.

Testinformation: This test detects the change in the SCN4A gene.

Rudolph, J. A., Spier, S. J., Byrns, G., Rojas, C. V., Bernoco, D., & Hoffman, E. P. (1992). Periodic paralysis in quarter horses: a sodium channel mutation disseminated by selective breeding. Nature Genetics, 2(2), 144-147. doi: 10.1038/ng1092-144.

Further information is available at Online Mendelian Inheritance in Animals.

Breeds affected:

Test #: H107

Sample: Blood, Hair

Price: 35 € (net)

Time required: 10-14 days


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