Epidemiology

The strongest risk factor for developing a psychotic disorder (including schizophrenia) is family history. Having a parent with schizophrenia leads to a relative risk (RR) of 7.5.

Risk of developing schizophrenia

• monozygotic twin has schizophrenia = 50%
• parent has schizophrenia = 10-15%
• sibling has schizophrenia = 10%
• no relatives with schizophrenia = 1%

Other selected risk factors for psychotic disorders include:

• Black Caribbean ethnicity - RR 5.4
• Migration - RR 2.9
• Urban environment- RR 2.4
• Cannabis use - RR 1.4

Factors associated with poor prognosis

• strong family history
• gradual onset
• younger age of onset (especially in males)
• male sex
• low IQ