1984; Kety, 1987; Kendler et al., 1994; Kety et al., 1994; Tienari et al., 2000, 2003). However, adoption studies have also demonstrated that the adopted-away children of mothers with schizophrenia only have a higher risk of developing the disorder when other psychological abnormalities are present in the adoptive family (Tienari et al., 2000, 2003; Wynne et al., 2006). Children of healthy biological parents who are adopted by a family with parents affected by schizophrenia do not themselves have an increased risk of developing the disorder. These studies demonstrate the influence of genetic factors on the vulnerability to schizophrenia, but they also clearly demonstrate that environmental factors contribute substantially to the manifestation of the disorder. Individuals with schizophrenia often suffer from other co-morbid psychiatric conditions. Epidemiological studies have revealed an increased prevalence of depression, anxiety disorders, and substance abuse disorders in schizophrenia patients compared to the general population (for review see Buckley et al., 2009). There is also substantial evidence for an overlap between schizophrenia and bipolar disorder. For example, relatives of patients with bipolar disorder have an increased risk of developing schizophrenia and vice versa (Valles et al., 2000; Cardno et al., 2002; Maier et al., 2002; Laursen et al.,
