Genetics of fear and anxiety disorders.

From protozoa to mammals, organisms have been selectively bred for genetic differences in defensive behaviour which are accompanied by differences in brain and other biological functions. Studies of twins indicate some genetic control of normal human fear from infancy onwards, of anxiety as a symptom and as a syndrome, and of phobic and obsessive-compulsive phenomena. Anxiety disorders are more common among the relatives of affected probands than of controls, especially among female and first-degree relatives; alcoholism and secondary depression may also be over-represented. Familial influences have been found for panic disorder, agoraphobia, and obsessive-compulsive problems. Panic disorder in depressed probands increases the risk to their relatives of phobia as well as of panic disorder, major depression, and alcoholism. The strongest family history of all anxiety disorders is seen in blood-injury phobia; even though it can be successfully treated by exposure, its roots may lie in a genetically determined specific autonomic susceptibility. Some genetic effects can be modified by environmental means.