Another sign of the structurally altered signal processing in the central nervous system in this group of people is the conspicuously common Paradoxical reaction (c. 10–20% of patients). These are unexpected reactions in the opposite direction as with a normal effect, or otherwise significant different reactions. These are reactions to neuroactive substances such as local anesthetic at the dentist, sedative, caffeine, antihistamine, weak neuroleptics and central and peripheral painkillers. Since the causes of paradoxical reactions are at least partly genetic, it may be useful in critical situations, for example before operations, to ask whether such abnormalities may also exist in family members