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Due to the large number of factors that can lead to Exertional Myopathy, it is important to investigate if there are genetic predispositions or defects when beginning the diagnostic process and when clarifying differential diagnoses.

With the knowledge of the genetic make-up of an animal, existing environmental or medical co-factors can be assessed on a case-specific basis to inform initial therapies and appropriate adjustments in the future.

Understanding the MIM 6 variant (previously “PSSM2”) Test

1. n/n: none of the tested genetic mutations is present

All tested variants are normal (wild-type).

If symptoms are present, the cause lies in other factors or in genetic mutations which have not yet been identified.


2. n/P*: the tested genetic mutation is present in heterozygosity

The presence of one or more genetic defects affects the structure and/or function of the muscle. Younger animals are generally more able to compensate for environmental stressors that trigger symptoms in adults, at least with correct management. If younger animals show symptoms of exertional myopathy and have only a small number of the six tested genetic variants, other factors from the categories of “Management” and/or “Metabolism” are likely to be involved.

A comprehensive investigation of all co-factors (environmental and hereditary) is necessary to appropriately assess a specific animal’s risk of developing symptoms.

Details on the individual variants can be found at MIM-Variants ("PSSM2") and associated genes.



3. P*/P*: the tested genetic mutation is present in homozygosity

When both copies of a gene are mutated, both of the encoded proteins are affected, and there is no normal version to compensate for the defect. Increasing the number of individual risk factors generally increases the potential severity of symptoms.

In such “high risk” genetic profiles, optimized management is essential. Even small deviations from a stabilizing management protocol, or increased demands on the “metabolism” of the muscle is sufficient to trigger symptoms.

Differential Diagnosis


  • Clostridium sp., Influenza, Streptococcus equi, Sarcocystis, Borreliose

  • New Equine Virus (NEV)


Internal Disorders

  • Colic

  • Pleuropneumonia

  • Aortic arch Thrombosis

  • Neurological Disorders

  • Intravascular hemolysis and bilirubinuria

  • Rhabdomyolysis through physical exertion

  • Nutrition-related Myodegeneration (Vitamin E deficiency, Selenium deficiency)

  • Poisoning (eg. Toxic plants)ergiftungen


Musculoskeletal Disorders

  • Lameness due to skeletal or tendon/ligament disorders

  • Laminitis

  • Fractures

  • Spinal abnormalities (eg. Equine Cervical Vertebral Malformation, ECVM)