Malignant hyperthermia (MH) is a hereditary metabolic myopathy triggered by certain anaesthetics (so-called volatile anaesthetics and succinylcholine). Typical clinical symptoms are rigid muscles of the jaw (masseter spasm), generalized muscle rigidity, release of muscle protein into the urine (myoglobinuria), an abnormally rapid or irregular heartbeat (cardiac arrhythmia), rapid breathing, electrolyte disturbances and, mostly at a later stage, rapidly increasing body temperature.
Effective treatment of an MH crisis is based on the administration of the drug dantrolene. If untreated, an MH crisis can be fatal. The estimated frequency of MH crises lies between 1:3.000 and 1:50.000 anaesthesias, the estimated frequency of genetic MH predisposition may even range between 1:2.000 and 1:3.000. MH predisposition is autosomal dominantly inherited, i.e. each carrier of the predisposition is clinically at risk and transmits the predisposition to 50 percent of his offspring Thus, the genetic diagnosis is meaningful for other family members, too. Up to now, two genes have been identified whose mutations can be causative for MH predisposition: In 70-80 percent of cases, MH is caused by a defect of the ryanodine receptor type 1 (RYR1), about 1 percent of cases are due to a defect of the dihydropyridine receptor (CACNA1S).
The diagnosis in patients with suspected MH can be made in (non human genetic) special laboratories by an extensive and invasive method, the so-called in vitro contracture test, on a muscle biopsy exposed to halothane and caffeine. In contrast, molecular genetic testing for causal mutations of the RYR1 and CACNA1S genes enables an accurate diagnosis with just a blood sample. Furthermore, the identification of a causative mutation in a family allows predictive genetic testing of at-risk asymptomatic family members.
After diagnosis, the patients receive a medical alert card or the like (e.g. bracelet) to inform the attending physicians about the MH predisposition particularly in emergency situations.
Familial clustering of cancers may indicate that hereditary factors play an important role for cancer development in such families. Genetic counselling and molecular genetic diagnostics may enable targeted preventive screening measures and might be important for individual treatment in some tumour entities.