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 alanine with threonine at codon 140 of the RYR1 protein, p.(Ala140Thr). The maximum allele frequency for this variant among the six major gnomAD populations is NFE: 0.0002, 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 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), this does not meet the requirement for PS4 (PMID:21455645). This variant has been identified in one individual with a negative IVCT/CHCT results, BS2_Moderate (PMID:21455645). 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, PM1 (PMID: 21118704). A REVEL score >0.85 (0.261) supports a benign status for this variant, BP4. Based on using Bayes to combine criteria this variant is classified as Likely Benign (PMID: 29300386). Criteria implemented: BS2_Moderate, PM1, BP4.