Since in general complex neurodevelopmental disorders have an estimated heritability lower than 100% (Table 2), their aetiology includes another component that is thought to be primarily the environment (e.g. stressful life events). Numerous factors acting during early development of a foetus may contribute to the genesis of a neurodevelopmental disorder, including insufficient maternal nutrition, daily smoking, viral infection and repeated psychological stress [182]. Most environmental vulnerability factors are however difficult to assign and quantify.
