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 2508 of the RYR1 protein, p.(Arg2508His). This variant is not present in the six major gnomAD populations at the time this variant was interpreted. This variant has been reported in nine unrelated individuals who have a personal or family history of a malignant hyperthermia reaction, six 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, PMID:23460944, PMID:25960145). This variant was determined to be de novo without confirmed parentage in one individual, PS2/PM6_Supporting (PMID:17483490). Functional studies in HEK293 cells show an increased sensitivity to RYR1 agonists, PS3_Moderate (PMID:26381711, PMID:27586648). This variant does not reside in a hotspot for pathogenic variants that contribute to MHS. A REVEL score >0.85 (0.898) supports a pathogenic status for this variant, PP3_Moderate. This variant has been classified as Likely Pathogenic. Criteria implemented: PS2/PM6_Supporting, PS3_Moderate, PS4, PP3_Moderate.