Malignant Hyperthermia (MH)Quick Summary
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Phenotype: Malignant hyperthermia (MH) is an inherited disease in which affected horses can be triggered by halogenated anesthetics, succinylcholine, stress, or excitement, which can induce a hyper-metabolic state characterized by symptoms including muscle contracture, elevated temperature, and an irregular heart rhythm.
Mode of Inheritance: Autosomal dominant
Alleles: N = Normal/Unaffected, MH = Malignant hyperthermia
Breeds appropriate for testing: Quarter Horse and related breeds
Explanation of Results:
- Horses with N/N genotype will not have malignant hyperthermia and cannot transmit this malignant hyperthermia variant to their offspring.
- Horses with N/MH genotype will be affected by malignant hyperthermia. They can transmit this malignant hyperthermia variant to their offspring. Matings with N/N genotype will result in a 50% chance of producing a malignant hyperthermia-affected foal.
- Horses with MH/MH genotype will have malignant hyperthermia.
$45 one test per animal
+ $15 each additional test from list below:
- Glycogen Branching Enzyme Deficiency (GBED)
- Hereditary Equine Regional Dermal Asthenia (HERDA)
- Hyperkalemic Periodic Paralysis (HYPP)
- Myosin-Heavy Chain Myopathy (MYHM)
- Polysaccharide Storage Myopathy (PSSM1)
$100 entire Quarter Horse & Related Breeds Disease Panel (5-panel plus) (all 6 tests)
Quarter Horse & Related Breeds Disease Panel (5-panel plus)
$100 per animal
AQHA recording fee may apply
Sample Collection
Horse DNA tests are carried out using cells from the roots of a hair sample (roughly 20-30 hairs).
1. Grab about 10 hairs at the base.
2. Wrap the hairs around your finger and give it a quick pull.
3. Check the ends to make sure the pulled hairs have roots.
4. Repeat the process until you have collected about 20-30 hairs with intact roots.
5. You can choose different places on the mane or tail. NOTE: For foals, we recommend pulling all hairs from the tail only.
6. Tape the hairs to the submission form and fold the form along the dotted line to protect the sample. Do not use ziploc bags as they can cause condensation that allows mold to grow on the hair.
7. Place the folded form containing the sample in a paper envelope and mail it to the laboratory.
Malignant hyperthermia (MH) is an inherited disease that causes a life-threatening condition in susceptible horses triggered by exposure to halogenated anesthetics or succinylcholine, and occasionally by stress or excitement. This genetic condition has been identified in Quarter Horses and American Paint Horses.
MH is inherited as an autosomal dominant trait so that only one copy of the MH allele is required to cause disease. A missense mutation (c.7360C>G) in the RyR1 gene results in an altered protein product (p.R2454G). The RYR1 gene provides instructions for making the protein called ryanodine receptor 1. Ryanodine receptors form channels that when activated release positively charged calcium ions from storage sites within skeletal muscle cells. The defective ryanodine receptor 1 of MH horses results in excessive release of calcium ions inside skeletal muscle cells, which then triggers a hyper-metabolic state that can be fatal.
Signs of MH episodes include muscle contracture (rigidity), elevated body temperature (> 40°C), elevated heart rate, irregular heart rhythm, excessive sweating, and shallow breathing. Presence of the MH mutation also results in more severe clinical tying-up phenotype in horses that have the PSSM1 mutation.
This diagnostic DNA test for MH allows identification of horses that have this mutation and are at risk of developing clinical signs of the disease, especially if subjected to anesthesia. This test is recommended for Quarter Horses, Paints and related breeds. This DNA test will also assist veterinarians to use appropriate medication for surgical procedures and make the correct diagnosis of the cause of a tying-up event.
