An increased sensitivity to 4-CmC has been linked to patients with malignant hyperthermia (Herrmann-Frank et al., 1996a; Baur et al., 2000) and ratiometric calcium imaging has been used to show hypersensitivity of 4-CmC in muscle cells from a patient with a mutation in RyR1 associated with malignant hyperthermia susceptibility (Roesl et al., 2014). The gene discussed is RYR1; the disease is cancer.