Genetic and functional analysis of the RYR1 mutation p.Thr84Met revealed a susceptibility to malignant hyperthermia

Purpose The aim of this study was to analyze the genetic and functional role of a novel RYR1 variant c.251 C > T (p.Thr84Met) identified in a patient with muscle weakness demonstrating MH susceptibility. Methods DNA testing of family members was conducted for assessment of pathogenicity of the genetic variant. For functional analysis, Ca.sup.2+ measurement using patient-derived myotubes and p.Thr84Met RYR1-transfected human embryonic kidney (HEK)-293 cells was performed to evaluate reactivity to RYR1 activators. The half-maximal effective concentration (EC.sub.50) values of two RYR1 activators, caffeine and 4-chloro-m-cresol (4CmC), were calculated from the acquired dose-response curves. The EC.sub.50 was compared between two groups: for myotubes, the control group and the patient, and for HEK-293 cells, WT and p.Thr84Met. Results Dose-response curves for caffeine and 4CmC were shifted to the left in both myotubes and HEK-293 cells compared to controls. The 50% effective concentration values for caffeine and 4CmC were significantly lower in both myotubes and HEK-293 cells compared to controls (P < 0.001 for all comparisons). Conclusions Our results of functional testing indicated RYR1 hypersensitivity to caffeine and 4CmC. We conclude that the genetic variant was associated with MH susceptibility.
Author(s): Takashi Kondo [sup.1] , Toshimichi Yasuda [sup.2] , Keiko Mukaida [sup.3] , Sachiko Otsuki [sup.1] , Rieko Kanzaki [sup.1] , Hirotsugu Miyoshi [sup.1] , Hiroshi Hamada [sup.2] , Ichizo [...]