A rare dominantly inherited genetic disorder that becomes apparent only when the person concerned has a general anaesthetic with a combination of an inhalation anaesthetic and a muscle-relaxant drug. A life-endangering rise in temperature occurs, with muscular rigidity, TACHYCARDIA, ACIDOSIS and SHOCK. About 1:20,000 patients having general anaesthesia suffer from this disorder, which progresses rapidly and can even be fatal. Surgery and anaesthesia must be stopped immediately and appropriate corrective measures taken, including the intravenous administration of DANTROLENE. It is important that when a case is identified, relatives are screened to ascertain if they have the condition.