This pathogenicity assessment is relevant only for malignant hyperthermia susceptibility (MHS) inherited in an autosomal dominant pattern. Variants in RYR1 can also cause other myopathies inherited in an autosomal dominant pattern or in an autosomal recessive pattern. Some of these disorders may predispose individuals to malignant hyperthermia. RYR1 variants may also contribute to a malignant hyperthermia reaction in combination with other genetic and non-genetic factors and the clinician needs to consider such factors in making management decisions. This sequence variant predicts a substitution of arginine with glycine at codon 401 of the RYR1 protein, p.(Arg401Gly). The maximum allele frequency for this variant among the six major gnomAD populations is NFE: 0.000009, a frequency consistent with pathogenicity for MHS. This variant has been reported in an individual with a personal or family history of an MH episode without in vitro contracture test (IVCT) or caffeine halothane contracture test (CHCT) results, this does not meet the criteria for PS4 to be implemented (PMID:16917943). No functional studies were identified for this variant. This variant resides in a region of RYR1 considered to be a hotspot for pathogenic variants that contribute to MHS, use PM1_Supporting to avoid overweighting with PM5 (PMID: 21118704). Another variant has been assessed as pathogenic occurs at this codon, p.(Arg401His), PM5. A REVEL score >0.85 (0.865) supports a pathogenic status for this variant, PP3_Moderate. Based on using Bayes to combine criteria this variant is assessed as a Variant of Uncertain Significance, (PMID: 29300386). Criteria implemented: PM1_Supporting, PM5, PP3_Moderate.