Patients with MmD secondary to mutations in the RYR1 gene may be at risk of malignant hyperthermia reactions, an abnormal response to muscle relaxants such as succinylcholine and volatile anaesthetics [27,81], as has been reported in few cases [28,29]; minicores on muscle biopsy have also been noticed in few patients with RYR1-related MH susceptibility but no other clinical features of a congenital myopathy [30,31]. This evidence concerns the gene RYR1 and congenital myopathy.