Primary myotubes as an alternative to the calcium induced calcium release test in diagnosing malignant hyperthermia susceptibility

Malignant hyperthermia (MH) is caused by the dysregulation of calcium (Ca 2+ ) in skeletal muscle cells. In this study, we evaluated the accuracy of a method for diagnosing susceptibility to MH using myotubes as an alternative to Ca 2+ -induced Ca 2+ release rate (CICR) test. In this retrospective study, we retrospectively analyzed Ca 2 ⁺ kinetics data obtained using fura-2/AM from myotubes that had been cultured from remnant muscle fibers of 98 patients who had previously undergone CICR testing for MH susceptibility in Japan. The 50% effective concentrations (EC 50 ) of caffeine and 4-chloro-m-cresol (4-CmC) were calculated from the concentration response curves. The previously calculated cut-off values (caffeine: 3.62 mM, 4-CmC: 197 μM) were used to diagnose susceptibility to MH. The diagnostic accuracy of myotubes was compared with that of the CICR test. Statistical significance was tested using the Mann–Whitney U test. The CICR test identified 76 patients as CICR-Positive and 22 patients as CICR-Negative. The EC 50 for caffeine was 2.9 (2.4–3.3) and 5.0 (4.5–5.5) mM in the CICR-Positive and CICR-Negative groups, respectively ( p < 0.0001). The EC 50 of 4-CmC was 130 (116–148) and 249 (226–289) μM in the CICR-Positive and CICR-Negative groups, respectively ( p < 0.0001). The sensitivity for caffeine for myotubes was 98.7% (95%CI 92.9–99.9). The specificity for caffeine was 100% (95%CI 85.1–100.0). The sensitivity and specificity for 4-CmC were 100% (95%CI 95.2–100.0) and 100% (84.5–100.0), respectively. Myotubes responses to caffeine and 4-CmC can be regarded as a viable alternative to the conventional CICR test; however, further validation is needed before this test supersedes the CICR.