Why are predictions about malignant hyperthermia not reliably based on family history?

• A. Anesthesia is always safe for MH patients.
• B. Only succinylcholine triggers MH.
• C. Predictions are inconsistent and cannot be relied upon.
• D. Genetic testing is always required before surgery.

Answer: (C)

Malignant hyperthermia susceptibility is a pharmacogenetic condition with variable expression. A family history isn’t a reliable predictor because the underlying mutations show incomplete penetrance and genetic heterogeneity—so a carrier may never exhibit a crisis, a person with no family history can still be susceptible due to a de novo mutation or unrecognized reactions in relatives, and multiple genes can be involved. Because a crisis requires exposure to triggering anesthetics, relying on whether relatives were affected misses cases and overestimates safety in others. For these reasons, predictions based solely on family history are inconsistent and cannot be trusted.