The genetic relationship of personality to major depression and schizophrenia

Since ancient times, dimensions of personality have been linked with the liability to psychiatric illness. In modern times, several research approaches suggest that personality and the liability to psychiatric illness such as schizophrenia and major depression (MD) are influenced by many of the same genes. If this is true, it could shed light on the genetic architecture of psychiatric illness. It could also validate the use of personality measures in unaffected relatives in linkage and association studies of psychiatric illness. This approach could potentially increase statistical power to detect genetic effects. The personality trait neuroticism (N) may be genetically related to MD, while schizotypal traits may be genetically related to schizophrenia. Twin studies have reported that most of the covariation between N and MD is due to shared additive genetic factors. Adoption studies have demonstrated that the biological offspring of schizophrenic mothers are more likely to have schizotypal personality disorder than are children of control mothers. At the current time, only one genome wide scan of N has been published, which does show some overlap in linkage results with genome scans of MD. However, this should be replicated and more rigorously studied. At the present time, there are no established susceptibility genes for MD. When these are established, it will be necessary to assess their relationship with N. Currently, no genome scans of schizotypy have been published. Furthermore, although several putative susceptibility genes for schizophrenia have been reported and replicated, only one--catechol-O-methyltransferase (COMT)--has been tested in schizotypy.