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 histidine at codon 2454 of the RYR1 protein, p.(Arg2454His). The maximum allele frequency for this variant among the six major gnomAD populations is AFR: 0.000062, a frequency consistent with pathogenicity for MHS. This variant has been reported in 34 unrelated individuals who have a personal or family history of a malignant hyperthermia reaction, all of these individuals had a positive in vitro contracture test (IVCT) or caffeine halothane contracture test (CHCT) result (if the proband was unavailable for testing, a positive diagnostic test result in a mutation-positive relative was counted, PS4 (PMID: 30236257, 12059893, 16163667, 24433488, 11575529, 10051009, 10823104, 17081152, 20618998, 21455645, 23460944, 23558838, 25960145). This variant has been identified in an individual with a negative IVCT/CHCT result, BS2_Moderate (PMID: 30236257). Functional studies in HEK293 cells show an increased sensitivity to RYR1 agonists, PS3_Moderate (PMID: 27586648). An ex vivo assay in patient derived immortalized lymphoblastoid cells also shows an increased sensitivity to RYR1 agonists (PMID: 19191333). This variant resides in a region of RYR1 considered to be a hotspot for pathogenic variants that contribute to MHS, PM1 (PMID: 21118704). This variant segregates with MHS in at least 11 individuals/families PP1_Strong (PMID: 12059893, 10051009). A REVEL score >0.85 (0.923) supports a pathogenic status for this variant, PP3_Moderate. Based on using Bayes to combine criteria this variant is assessed as Pathogenic, (PMID: 29300386). Criteria implemented: PS3_Moderate, PS4, PM1, PP1_Strong, PP3_Moderate, BS2_Moderate.