The idea of gene-environment interaction is becoming increasingly influential. It can be defined as the genetic control of sensitivity to environmental factors or as the environmental control of the way genes work. One such interaction between nature and nurture is that between childhood trauma which has been associated with psychosis not only in schizophrenia but also in bipolar disorder. A study of 138 first-degree relatives (siblings or parents) of people with schizophrenia or bipolar disorder looked at the links between childhood trauma scores and schizotypy (unusual thought patterns that can be the precursor of either schizophrenia or bipolar disorder). They found that there was a link between childhood trauma and schizotypy in the relatives of the schizophrenia sufferers but not in the relatives of the bipolar sufferers suggesting that an interaction between a gene predisposing people to schizophrenia, and childhood trauma was behind the increase in schizotypy.
Schurhoff, F. ... [et al] Self -reported childhood trauma correlates with schizotypal measures in schizophrenia but not bipolar pedigrees Psychological Medicine 39(3) March 2009, 365-370