Investigators at Guy’s & St Thomas’ Hospital, London, UK, and other centers sequenced RYR1 in 39 unrelated families with rhabdomyolysis and/or exertional myalgia and identified 9 heterozygous RYR1 mutations in 14 families, 5 of them previously associated with malignant hyperthermia (MH). Index cases presented from 3 to 45 years with rhabdomyolysis, with or without exertional myalgia (n=12), but no or little associated weakness; CK levels were markedly increased during episodes. Rhabdomyolysis was triggered by exercise and heat, viral infection and drugs. Familial RYR1 mutations were confirmed in relatives. 
COMMENT. Patients presenting with unexplained rhabdomyolysis and/or exertional myalgia and other family members should be tested for RYR1 mutations.
Malignant hyperthermia susceptibility of core myopathies. Due to their genetic linkage to mutations in the ryanodine receptor gene (RYR1), core myopathies (in particular, central core disease) carry a high risk of malignant hyperthermia susceptibility during anesthesia.