Prevalence of clinical signs and factors impacting expression of myosin heavy chain myopathy in Quarter Horse-related breeds with the MYH1E321G mutation

Abstract

Background: The prevalence of clinical signs and factors triggering muscle atrophy and rhabdomyolysis associated with an MYH1E321G mutation in Quarter Horses and related breeds (QH) remain poorly understood. Hypothesis/Objectives: Determine the prevalence and potential triggers of atrophy and stiffness in horses homozygous reference (N/N), heterozygous (My/N), and homozygous (My/My) for the MYH1E321G mutation. Animals: Two-hundred seventy-five N/N, 100 My/N, and 10 My/My QH. Methods: A retrospective case-control study using a closed-ended questionnaire completed by clients of the Veterinary Genetics Laboratory at the University of California, Davis. History of clinical signs, disease, vaccination and performance were analyzed by genotype using contingency testing. Results: Atrophy occurred in proportionately more horses with MYH1E321G (My) than N/N QH and more frequently in My/My than My/N QH (P