Malignant Hyperthermia Susceptibility — a silent genetic trait that is completely benign until a single exposure to the wrong anesthetic triggers a potentially fatal hypermetabolic crisis in the operating room.
RYR1 and CACNA1S are on the ACMG SF v3.2 mandatory secondary findings list. Whole genome sequencing identifies malignant hyperthermia susceptibility — preventing an anesthetic crisis before surgery even begins.
Malignant Hyperthermia Susceptibility
Malignant hyperthermia susceptibility (MHS) is a pharmacogenomic disorder in which pathogenic variants in RYR1 (ryanodine receptor 1) or CACNA1S (L-type voltage-sensitive calcium channel alpha-1 subunit) cause abnormal calcium regulation in skeletal muscle sarcoplasmic reticulum. MHS is clinically silent under normal conditions but becomes life-threatening when susceptible individuals are exposed to triggering agents — volatile inhalational anesthetics (halothane, isoflurane, sevoflurane, desflurane) or succinylcholine (a depolarizing neuromuscular blocking agent). Incidence of MH crisis is estimated at 1 in 10,000 to 1 in 50,000 anesthetic exposures; susceptibility (MHS) is more common, estimated at 1 in 2,000-3,000.
During a malignant hyperthermia crisis, uncontrolled skeletal muscle calcium release causes a hypermetabolic state with rapidly rising temperature (>40°C), severe metabolic acidosis, hypercapnia, muscle rigidity, rhabdomyolysis, and cardiovascular instability. Without immediate treatment with dantrolene sodium (the specific MH antidote), mortality exceeds 70%; with prompt dantrolene administration and supportive care, mortality has fallen to approximately 1-2%. Despite this improvement, MH remains a leading cause of preventable anesthetic death — approximately 150 deaths occur annually in the United States among unrecognized susceptible patients.
RYR1 pathogenic variants account for approximately 70-80% of MH-susceptible families; CACNA1S variants account for approximately 1%. A substantial fraction of clinically MH-susceptible families (confirmed by caffeine-halothane contracture test) have no identifiable pathogenic variant, because hundreds of RYR1 variants have been described and many have not achieved sufficient evidence for ACMG pathogenic classification. Both RYR1 and CACNA1S are included on the ACMG SF v3.2 secondary findings list — variants in these genes discovered opportunistically during genome sequencing are required to be reported, reflecting the life-saving nature of preoperative identification. MH susceptibility is also associated with certain myopathies (King-Denborough syndrome, central core disease) caused by RYR1 variants.
Central core disease and multi-minicore disease — caused by the same RYR1 variants — are associated with MH susceptibility. Patients with these myopathies should be assumed susceptible to MH regardless of genetic testing results.
RYR1 is a massive 106-exon gene with hundreds of variants — many not validated by contracture testing. Whole genome sequencing detects all RYR1 and CACNA1S variants, and the ACMG SF v3.2 mandate means these results are reported in genome analysis.
Finding an MH susceptibility variant before the first surgery prevents a crisis that has no pre-anesthetic warning signs
Malignant hyperthermia susceptible individuals look and feel completely normal. They have no symptoms, no medical history, and no abnormal laboratory findings until the moment they receive a triggering anesthetic agent. The first clinical presentation of MH is often the crisis itself — in the operating room or recovery room, after anesthetic induction. Once the crisis begins, the diagnosis must be made clinically and dantrolene administered within minutes to prevent death. Pre-identification of susceptibility — through whole genome sequencing of RYR1 and CACNA1S — allows the anesthesiologist to use trigger-free anesthesia protocols before any exposure occurs, completely preventing the crisis.
RYR1 with 106 exons requires complete gene analysis — limited panels detect only the common variants
RYR1 is one of the largest genes in the human genome with 106 coding exons, and over 400 RYR1 variants associated with MH have been described. Targeted MH panels typically test for the subset of variants that have been validated by caffeine-halothane contracture test correlation — approximately 48-50 variants with strong evidence. The remaining hundreds of RYR1 variants exist in a classification gray zone. Whole genome sequencing sequences all 106 RYR1 exons and the complete CACNA1S gene, providing maximum sensitivity across the full variant spectrum. When a known pathogenic variant is identified, the result directly enables MRC precautionary anesthesia planning.
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Common questions about whole genome sequencing.
What is the difference between whole genome sequencing and a targeted genetic test?
Targeted genetic tests — including standard hereditary cancer panels — read a pre-defined list of known variants in a specific set of genes. They are designed to find what they already know to look for. Whole genome sequencing reads your entire genome: all 6 billion base pairs, every gene, every region between genes. A Mayo Clinic study published in JAMA Oncology found that standard testing guidelines missed more than half of patients with inherited cancer mutations. Genome Test does not have a fixed list.
What will I receive when my results are ready?
Your Dante Genome delivers 200+ physician-ready reports organized by clinical category — hereditary cancer, cardiac conditions, rare diseases, pharmacogenomics, carrier status, and more. Reports are delivered to your secure Genome Manager and are formatted for direct clinical use. Your genome data is permanently retained and re-analyzed automatically as science advances.
What happens if a clinically significant variant is found?
If a pathogenic or likely-pathogenic variant is identified, it will be clearly flagged in your physician-ready report with clinical context, published evidence, and recommended next steps. We recommend sharing any clinically significant finding with your physician or a genetic counselor, who can guide decisions about surveillance, risk reduction, or cascade testing for family members.
How is this different from a consumer DNA test like 23andMe or AncestryDNA?
Consumer DNA tests use genotyping chips that read less than 0.1% of your genome — a tiny pre-selected set of common variants. They are optimized for ancestry and population-level traits, not clinical genetic findings. The Dante Genome Test sequences 100% of your genome at 30X coverage, the same standard used in clinical diagnostic settings. The two tests are not comparable in scope, methodology, or clinical utility.
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Your collection kit ships within 48 hours of ordering. Once your sample arrives at our CLIA-certified laboratory, sequencing and analysis takes 6–8 weeks. Results are delivered securely to your Genome Manager, where you can access your reports, share them with your physician, and receive automatic updates as new findings are validated against your genome.
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