What Causes Schizophrenia
Schizophrenia is caused by a complex interaction between strong genetic factors (approximately 80% heritability) and environmental triggers, with no single gene or environmental factor being solely responsible. 1
Genetic Factors
Genetics represent the most important etiological component of schizophrenia, accounting for approximately 80% of the disease liability. 1 However, this is not a simple inheritance pattern:
- Multiple genes with small individual effects contribute to risk rather than a single causative gene. 1
- The 40-50% concordance rate in identical twins definitively proves that genetics alone cannot explain the disorder—if it were purely genetic, identical twins would show 100% concordance. 1
- Increased family history of schizophrenia and schizophrenia spectrum disorders (schizotypal or paranoid personality disorders) is consistently found in patients with the condition. 1
Environmental Risk Factors
Environmental factors interact with genetic vulnerability to trigger disease manifestation. Key environmental contributors include: 1
- Pregnancy and birth complications (including intrauterine fetal hypoxia) 1
- Childhood trauma 1
- Migration status 1
- Social isolation and urbanicity 1
- Substance abuse, particularly cannabis use 1
Neurobiological Mechanisms
The disorder ultimately converges on disturbances in specific neurotransmitter systems, regardless of the diverse initial triggers:
- Dopamine and glutamate systems are most consistently implicated in the pathophysiology. 1
- Neurobiological abnormalities include deficits in smooth-pursuit eye movements, autonomic responsivity, and progressive increases in ventricular size. 1
- Progressive decrease in cortical gray matter volume occurs during adolescence (4-fold greater than normal controls), with greatest differences in frontal and temporal regions. 1
What Does NOT Cause Schizophrenia
There is no evidence that psychological or social factors cause schizophrenia. 1 This is a critical distinction:
- Psychosocial stressors and family dynamics (including expressed emotion) influence the timing of onset, course, and severity—but do not cause the underlying disorder. 1
- Communication deficits found in families of patients are likely genetic traits rather than etiological agents. 1
- The relationship to socioeconomic status remains unclear and may reflect selection bias rather than causation. 1
Clinical Implications
Schizophrenia is best understood as a neurodevelopmental disorder where genetic vulnerability creates a substrate that environmental factors can trigger. 1 The multifactorial nature means: