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Immune Mediated Myositis (IMM)

Regular Price: 35,00  Special Price: 30,00 

 → Immune-mediated muscle wasting often triggered by infections or vaccination.

Instructions for ordering:

  1. Enter the information of the first horse for which you want to order the test
  2. Add to cart
  3. Go to cart to check out, or
  4. Enter the information for a second horse
  5. For sample collection follow the instructions here.
  6. You can use this template to send in hair samples.
  7. Please also send the completed order form together with the samples.

For a breeder or veterinarian discount please contact us before ordering.

Any information you include here is optional, but will be included on the certificate of results (except “Additional Info”).

Enter the name of your animal
Enter your animal's date/year of birth
Enter the breed name
Enter the registration number if known
Enter the microchip number
Is there anything else you would like to tell us about your horse? Reason for testing, symptoms etc.?

General Information

  • IMM is often triggered by environmental factors. In about 39% of reported IMM cases, horses had a history of recent infection or vaccination.
  • Mainly found in Quarter Horses and related breeds.
  • Affected horses usually show symptoms either before the age of 8 years or after the age of 17 years.
  • Muscle wasting may progress very quickly and last for several months.

→ Here you’ll find the IMM information for downloading and printing:


  • Muscle wasting (especially hindquarters)
  • Muscle stiffness
  • Weakness
  • Lymphocytes in muscular fibers

Inheritance and Genotypes

→ IMM is an incomplete autosomal dominant/semidominant hereditary disease. That means that horses with one or two copies of the genetic variant (n/IMM or IMM/IMM) are at risk-affected but animals with two copies are at higher risk to develop symptoms.

Genotype: The horse is: Effects:
n/n normal. The horse does not have any copies of the genetic variant causative for IMM and therefore cannot pass it on to any offspring.
n/IMM at risk-affected (heterozygous). The genetic variant causative for IMM will be passed on to its offspring with a probability of 50%. These 50% will also be at risk-affected (n/IMM).
IMM/IMM at high risk-affected (homozygous). The genetic variant causative for IMM will be passed on to all offspring. All offspring will be at risk-affected (n/IMM).


  • This test is best used to confirm a diagnosis of IMM. Because of the variable penetrance of this mutation (not all horses with the mutation will become sick), it is not yet clear how or if this test should be used for making breeding decisions. If a horse has become sick, it should not be used for breeding.


Gianino et al., (2019). Prevalence of the E321G MYH1 variant for immune-mediated myositis and nonexertional rhabdomyolysis in performance subgroups of American Quarter Horses. J Vet Intern Med. 33:897-901.

Valberg, S.J. et al. (2018). An E321G MYH1 mutation is strongly associated with nonexertional rhabdomyolysis in Quarter Horses. J Vet Intern Med.1-8.

Durward-Akhurst, S.A., Valberg, S.J. : Immune-Mediated Muscle Diseases of the Horse. Vet Pathol 55:68-75, 2018. Pubmed reference: 28129093. DOI: 10.1177/0300985816688755.

Finno et al. (2018). A missense mutation in MYH1 is associated with susceptibility to Immune-mediated myositis in Quarter Horses. Skelet Muscle 8(1):7.

Further information is available at Online Mendelian Inheritance in Animals.

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