Clinical and Genetic Characterization of a Novel RYR1 Variant (p.Gln474His) in Malignant Hyperthermia Susceptibility

Malignant hyperthermia (MH) is a life-threatening pharmacogenetic disorder of skeletal muscle calcium regulation and commonly associated with pathogenic variants in the RYR1 gene. Interpretation of rare RYR1 variants remains challenging, particularly when classified as variants of uncertain significance (VUS). This study describes the clinical, functional, and genetic evaluation of a patient with suspected MH susceptibility carrying a rare RYR1 mutation.

We report a retrospective case evaluation of a 32-year-old female referred for MH assessment following a prior peri-operative hypermetabolic event. Clinical records were reviewed, and MH susceptibility was assessed using the caffeine-halothane contracture test (CHCT). Genetic testing was performed using a targeted MH susceptibility gene panel, including RYR1, CACNA1S, and STAC3. Variant classification was conducted following American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines.

The patient demonstrated a positive CHCT, consistent with MH susceptibility. Genetic analysis identified a rare heterozygous RYR1 missense variant. No pathogenic or likely pathogenic variants were detected in CACNA1S or STAC3. Based on ACMG/AMP criteria, the RYR1 p.Gln474His variant is currently classified as a VUS. However, its localization within the N-terminal regulatory region of RyR1 and concordance with abnormal CHCT findings provide supportive functional context.

This case underscores the importance of integrating clinical history, functional contracture testing, and genetic data in the evaluation of MH susceptibility. While functional findings may support biological plausibility, definitive pathogenic classification of rare RYR1 variants requires additional segregation data or mechanistic studies.