RYR1 and Malignant hyperthermia: In addition, RyR1 mutations in muscle cause diseases such as multi-mini core disease (MMD), hypokalemic periodic paralysis, and malignant hyperthermia (MH), although the phenotype/genotype relationship is unclear (Fujii et al., 1991; Marchant et al., 2004; Treves et al., 2008; Wilmshurst et al., 2010).