Searching for major genes for psychiatric disorders.

Many of the major psychiatric disorders show sufficient familial clustering to raise the suspicion that genetic factors are important in determining who is and who is not affected. There is reasonable evidence from many sources to support a major genetic component to these common disorders. However, no simple mode of inheritance can be convincingly demonstrated. A genetic linkage study seems to be the most promising approach towards identifying aetiological factors in these disorders. The neurochemical complexity of the relevant parts of the brain and the absence of any biochemical abnormalities that appear to be aetiologically relevant also give strong impetus for a molecular genetic approach that uses genetic linkage. 'Large-scale' genetic linkage studies using restriction fragment length polymorphisms are under way for manic depressive illness (among other disorders) and are providing evidence against the involvement of some candidate genes. Some strongly positive evidence has also begun to emerge.