Myosin Heavy Chain 1 (MYH1 or IMM)

This abbreviation stands for Immune Mediated Myositis and is linked to the presence of the gene mutation MYH1 (Myosin Heavy Chain 1). It can cause sudden muscle wasting resulting in severe atrophy across the horse’s topline within two to three days, leaving the horse’s spine very visible. This form of muscle wasting can occur in Quarter Horses and related breeds, with reiners and reined cow horses being the most at risk. Dr Valberg’s research suggests that disease or inflammation are the triggers in affected horses. Testing for the MYH1 gene can be done at most of the major laboratories, such as Animal Genetics, Etalon and UC David in the US and at Generation/CAG, Laboklin or Animal Genetics, among others.