One obvious gene-environment link concerns the season in which birth took place. An excess of winter-spring births in bipolar disorder and schizophrenia has been observed [186]. A similar tendency has been found in schizoaffective disorder (December-March), major depression (March-May) and autism (March) [reviewed in 187]. Besides the season of birth, also the place of birth is thought to be associated. Urban–born (and brought-up) subjects are more susceptible to neurodevelopmental disorders than rural-born (and brought-up) subjects [188]. Furthermore, risk factors like immigration and adoption may contribute to the development of psychiatric disorders [189, 190].
