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 tryptophan at codon 328 of the RYR1 protein p.(Arg328Trp). The maximum allele frequency for this variant among the six major gnomAD populations is SAS: 0.00006 maf, a frequency consistent with pathogenicity for MHS. This variant has been reported in one proband with a personal or family history of a malignant hyperthermia reaction and a positive in vitro contracture test (IVCT) or caffeine halothane contracture test (CHCT) result (when the proband was unavailable for testing a positive diagnostic test result in a mutation positive relative was counted), PS4_Supporting (PMID:12883402). Functional studies in HEK293 cells show an increased sensitivity to RYR1 agonists, PS3_Moderate (PMID:12883402). This variant resides in a region of RYR1 considered to be a hotspot for pathogenic variants that contribute to MHS, ( PM1, PM1_Sup) (PMID: 21118704). This variant segregates with MHS in four individuals, PP1 (PMID:12883402). For these reasons, this variant has been classified as Likely Pathogenic. Criteria implemented: PS4_Supporting, PS3_Moderate, PM1, PP1.