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Hyperkalemic Periodic Paralysis (HYPP)
| Acronym: | HYPP |
| Gene: | SCN4A |
| Mutation: | c.4248C>G |
| Inheritance: | Autosomal Incompletely Dominant |
| Sample type: | WBE (Whole Blood EDTA), HA (Hairs - with roots) |
Genetics and characteristics
Hyperkalemic periodic paralysis (HYPP) is a disease characterized by muscle tremors. HYPP occurs in Quarter Horses and its crossbreeds, American Paint Horses and Appaloosas. Symptoms of HYPP vary between horses; some of them will experience only a few episodes of collapse or muscle tremors in their lifetime while some will present symptoms more often than not. HYYP can also cause lethal sudden paralysis followed by cardiac or respiratory failure. HYYP in horses is caused by a genetic mutation in the SCN4A gene which encodes a subunit of a sodium channel. This mutation produces abberant sodium channel proteins which release more sodium in the muscle tissue and cause involuntary muscle contractions.
HYYP is inherited as an autosomal co-dominant trait. This means that only one mutated gene is required for the disease to develop, but having two mutated genes leads to more severe symptoms. Early genetic testing is thus important to help the decision of selecting mating pairs.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (i.e. two pairs of healthy alleles). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
AFFECTED HETEROZYGOTE |
Tested mutation was detected in animal with „affected heterozygote“ result. Animal tested as affected heterozygote has one wild-type and one mutation allele, it is in heterozygous state. It is likely to develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has two copies of mutation alleles affecting the gene. It is likely the animal will experience a genetic disorder due to this mutation.** It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
**Penetrance of tested mutation, and potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
Pickar JG, Spier SJ, Harrold D, Carlsen RC. [3H]Ouabain binding in skeletal muscle from horses with hyperkalemic periodic paralysis. Am J Vet Res. 1993;54(5):783-787.
Naylor JM. Equine hyperkalemic periodic paralysis: Review and implications. Can Vet J. 1994;35(5):279-285.