German researchers suggest that environmental factors have a major impact on the onset of schizophrenia. They found that individuals exposed to four or more environmental risk factors, such as perinatal brain insults, cannabis use, neurotrauma, psychotrauma, urbanicity and migration, developed schizophrenia approximately 8 years sooner than those not exposed to risk factors.
In addition, it was found that polygenic risk scores had no effects on schizophrenia phenotypes, such as age at disease and prodrome onset, symptom severity, cognitive function, employment and hospital admissions. The researchers said, “This indicates that ‘schizophrenia risk score-based analyses might not be optimized for study of association with disease-relevant phenotypes.’”
For the study, Hannelore Ehrenreich and colleagues from the Max Planck Institute of Experimental Medicine in Göttingen, looked at 750 men with schizophrenia or schizoaffective disorder. They analyzed whether exposure to individual environmental risk factors was associated with disease severity and socioeconomic functioning. Researchers found perinatal complications, neurotrauma and cannabis use were all significantly associated with disease onset at a younger age and prodrome start.
However, what researchers found most striking was the when comparing patients without risk factor exposure to those with one or more environmental risks, they found that each additional risk increased the outcome. Having four or more risk factors was associated with schizophrenia onset 8 years earlier, 3 years less time spent in education, 39.5% more unemployment and 1.2 more hospital admissions, on average. Particularly cannabis use explained 10.2% of the variance in age at disease onset.
“This result calls for public education that targets prevention,” says the researchers, particularly as “age at onset of schizophrenia is a crucial determinant of an affected individual’s fate and the total socioeconomic cost of the illness.”