Ryanodine Receptor Isoform 1 (RYR1)

RYR1 is a protein channel that releases calcium in the muscle, causing the muscle to contract. Certain variations in the RYR1 gene cause the muscles to be very sensitive to some medications. This can lead to a serious side effect called malignant hyperthermia which may occur after exposure to certain medicines. Clinical features of malignant hyperthermia include prolonged muscle contraction which can lead to a fast or irregular heartbeat, fever, and possibly severe muscle breakdown if untreated.  Genetic testing of the RYR1 gene and the related CACNA1S gene can assist in identifying patients at high risk of developing malignant hyperthermia (MH).

Priority phenotype

• Increased risk of developing malignant hyperthermia – Patients who have inherited a known malignant hyperthermia-causative variant (also called pathogenic variant) in the RYR1 gene are susceptible to developing malignant hyperthermia when exposed to the depolarizing neuromuscular blocker succinylcholine and/or the volatile inhaled anesthetics (enflurane, methoxyflurane, desflurane, halothane, isoflurane, sevoflurane). Less than 0.07% of people have a known malignant hyperthermia -causative variant in RYR1 or CACNA1S.
• Drugs we recommend to avoid due to a high risk of developing malignant hyperthermia:
  • Halogenated volatile anesthetics: Enflurane, methoxyflurane, desflurane, halothane, isoflurane, sevoflurane. Use alternative anesthetic medications such as propofol supplemented by benzodiazepines, opioids, nitrous oxide, and regional anesthetic techniques if needed. Amide and ester local anesthetic agents can be used in these patients.
  • Depolarizing neuromuscular blocker: Succinylcholine. Use non-depolarizing neuromuscular blockers such as mivacurium, atracurium, rocuronium, pancuronium, cisatracurium, and vecuronium.

Routine phenotype

Normal risk of developing malignant hyperthermiaUncertain malignant hyperthermia susceptibility – In patients with this genotype, the risk of developing malignant hyperthermia after exposure to succinylcholine or halogenated volatile anesthetics is the same as the general population. cannot be determined by genotype alone.  It should be noted that these medicines might still cause malignant hyperthermia even for people in this category. Family history, clinical findings, and other laboratory tests should be considered in making clinical decisions regarding anesthetic agent selection.