Risk of malignant hyperthermia in patients carrying a variant in the skeletal muscle ryanodine receptor 1 gene

Malignant hyperthermia is a life-threatening disorder, which can be prevented by avoiding certain anesthetic agents. Pathogenic variants in the skeletal muscle ryanodine receptor 1-gene are linked to malignant hyperthermia. We retrospectively studied 15 patients who presented to our clinic with symptoms of muscle dysfunction (weakness, myalgia or cramps) and were later found to have a variant in the skeletal muscle ryanodine receptor 1-gene. Symptoms, creatine kinase levels, electromyography, muscle biopsy and in vitro contracture test results were reviewed. Six out of the eleven patients, with a variant of unknown significance in the skeletal muscle ryanodine receptor 1-gene, had a positive in vitro contracture test, indicating malignant hyperthermia susceptibility. In one patient, with two variants of unknown significance, both variants were required to express the malignant hyperthermia-susceptibility trait. Neurologists should consider screening the skeletal muscle ryanodine receptor 1-gene in patients with myalgia or cramps, even when few to no abnormalities on ancillary testing.