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Horse Malignant Hyperthermia (MH)
| Acronym: | MH |
| Gene: | RYR1 |
| Mutation: | c.7360C>G |
| Inheritance: | Autosomal Dominant |
| Sample type: | WBE (Whole Blood EDTA), HA (Hairs - with roots) |
Genetics and characteristics
Malignant hyperthermia (MH) is a disease characterized by elevated body temperature, irregular heartbeats and muscle contraction. This condition is triggered when a horse is exposed to certain anesthetic drugs and during high stress or excitement. So far, MH has been reported in Quarter horses, Arabians, Thoroughbreds and ponies. It is caused by a genetic mutation in the RyR1 gene which encodes the protein called ryanodine receptor 1. These receptors form ion channels in the cell membrane responsible for calcium release in skeletal and cardiac muscles. The mutation leads to excessive calcium release, which induces a hyper-metabolic state. This hyper-metabolic state can be fatal due to rhabdomyolysis, respiratory and metabolic acidosis.
MH is inherited as an autosomal dominant trait. This means that only one mutated gene is required for the disease to develop. Early genetic testing is thus important to inform the decision when 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:
Lanner JT, Georgiou DK, Joshi AD, Hamilton SL. Ryanodine receptors: structure,expression, molecular details, and function in calcium release. Cold Spring Harb Perspect Biol. 2010;2(11). doi:10.1101/cshperspect.a003996