Because of the large number of cell divisions during spermatogenesis, the mutation 
rate for base substitutions is much higher in men than in women, and increases with 
paternal age. This association has been investigated, and findings have offered 
a de novo mutations explanation for schizophrenia. 

Advanced Paternal Age

- Prolonged delay between pregnancies may also be associated with an increased 
risk of schizophrenia.
- Using a population-based study to examine the relationship, longer 
spring conception times (>12 months) were associated with a modest increase in risk of 
schizophrenia. 

Prolonged Delay Between Pregnancies

- Socioeconomic factors too may play a role in the development of schizophrenia. Living in an urban environment as compared to a rural one is associated with greater exposure to pollution and stress, and increased health risk behaviors (e.g., 
smoking, drinking, and substance abuse). 
- These factors may increase an individual’s susceptibility to developing psychosis by affecting cognitive and neural development. 

Socioeconomic Factors

We have classified “preconception” environmental risk factors as those involving demographic or other parental features potentially identifiable prior to conception.

Arizona State University

- Every major review for the past half-century, including those authored by members 
of our group, has described schizophrenia as a disease of “unknown etiology,” one 
“suspected” of having developmental origins. While this is a valid characterization 
of an enigmatic disease, its consistent application belies the advances made in the 
field of schizophrenia research.
- For example, multiple risk factors for the disease have now been elucidated. 
Some meet the standard of reproducibility, and several findings have been replicated in population-based studies. Additionally, risk and vulnerability at key points 
throughout the lifespan have been investigated, and outcomes in this area have 
strengthened the plausibility and consistency of possible developmental origins. 


- Preconceptual
- Prenatal
- Perinatal

Environmental Risk Factors of Schizophrenia

Opler, M., Charap, J., Greig, A., Stein, V., Polito, S., & Malaspina, D. (2013). Environmental risk factors and schizophrenia. International Journal of Mental Health, 42(1), 23-32. https://doi.org/10.2753/IMH0020-7411420102

Environmental Risk Factors and Schizophrenia

Preconceptual Risk Factors for Schizophrenia

Studies have found that individual for schizophrenia is 2x higher in fraternal twins than in siblings. Fraternal twins are genetically the same as siblings in that they are two separate eggs and two separate sperms that just happen to fertilize at the same time. So the fact that risk of schizophrenia is so much higher in fraternal twins than siblings suggests that the shared environment of the womb while they are fetuses is a key contributor to the development of schizophrenia. 

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