Functional analysis of<i>RYR1</i>variants linked to malignant hyperthermia

Abstract

Malignant hyperthermia manifests as a rapid and sustained rise in temperature in response to pharmacological triggering agents, e.g. inhalational anesthetics and the muscle relaxant suxamethonium. Other clinical signs include an increase in end-tidal CO₂, increased O₂ consumption, as well as tachycardia, and if untreated a malignant hyperthermia episode can result in death. The metabolic changes are caused by dysregulation of skeletal muscle Ca²⁺ homeostasis, resulting from a defective ryanodine receptor Ca²⁺ channel, which resides in the sarcoplasmic reticulum and controls the flux of Ca²⁺ ions from intracellular stores to the cytoplasm. Most genetic variants associated with susceptibility to malignant hyperthermia occur in the <i>RYR1</i> gene encoding the ryanodine receptor type 1. While malignant hyperthermia susceptibility can be diagnosed by <i>in vitro</i> contracture testing of skeletal muscle biopsy tissue, it is advantageous to use DNA testing. Currently only 35 of over 400 potential variants in <i>RYR1</i> have been classed as functionally causative of malignant hyperthermia and thus can be used for DNA diagnostic tests. Here we describe functional analysis of 2 <i>RYR1</i> variants (c. 7042_7044delCAG, p.ΔGlu2348 and c.641C>T, p.Thr214Met) that occur in the same malignant hyperthermia susceptible family. The p.Glu2348 deletion, causes hypersensitivity to ryanodine receptor agonists using <i>in vitro</i> analysis of cloned human <i>RYR1</i> cDNA expressed in HEK293T cells, while the Thr214Met substitution, does not appear to significantly alter sensitivity to agonist in the same system. We suggest that the c. 7042_7044delCAG, p.ΔGlu2348 <i>RYR1</i> variant could be added to the list of diagnostic mutations for susceptibility to malignant hyperthermia.