MYH1 Myopathy / Immune-mediated Myositis (IMM)

MYH1 Myopathy is a hereditary disease with incomplete/semi-dominant inheritance, caused by a mutation (chr11:52993878T>C; E321G) in the MYH1 Myosin Heavy Chain 1 gene. This mutation is a major risk factor horse horses to develop Immune mediated myopathy (IMM) and non-exertional rhabdomyolysis. IMM affected animals can exhibit muscle extreme loss (especially in the hind quarters), muscle stiffness, and overall weakness. Horses with episodes of non-exertional rhabdomyolysis exhibit muscle damage (with or without atrophy) causing muscle stiffness and cramping, dark urine, and high muscle enzyme levels in the blood.