Schizophrenia is linked to over 100 genetic tags. However, having a genetic predisposition, or having a relative with schizophrenia, doesn't necessarily mean that you will develop schizophrenia. Late adolescence and early adulthood is the time where it most commonly manifests.
Psychological and social pressures can precipitate the illness or make it worse. It is important to look at schizophrenia as being an interaction between the person and his/her environment. Many genetic epidemiological studies have shown, for more than 50 years, that genetic factors contribute substantially, but not exclusively, to the underlying cause of schizophrenia.