Accumulated environmental risks have substantial impact on schizophrenia

By Laura Cowen, medwireNews Reporter

Accumulation of environmental risk factors has a “huge” effect on age at schizophrenia onset, German researchers report.

They found that individuals with four or more environmental risk factors develop the disease approximately 8 years earlier than those not exposed to well-studied schizophrenia risk factors, such as perinatal brain insults, cannabis use, neurotrauma, psychotrauma, urbanicity and migration.

By contrast, polygenic risk scores generated using comprehensive genome-wide association study data had no detectable effects on important schizophrenia phenotypes, namely age at disease and prodrome onset, symptom severity, cognitive function, employment and hospital admissions.

This indicates that “schizophrenia risk score-based analyses might not be optimised for study of association with disease-relevant phenotypes”, say the researchers.

The study included 750 men with schizophrenia or schizoaffective disorder from the Göttingen Research Association for Schizophrenia dataset.

Hannelore Ehrenreich and colleagues, from the Max Planck Institute of Experimental Medicine in Göttingen, first looked at whether exposure to individual environmental risk factors up to the age of 18 years, which they consider to be the most vulnerable time of brain development, was associated with measures of disease severity and socioeconomic functioning.

They report in The Lancet Psychiatry that perinatal complications, neurotrauma and cannabis use (ranging from any consumption up to regular use) were all significantly associated with younger age at disease onset and prodrome start.

Perinatal complications and cannabis use were associated with increased hospital admissions, while psychotrauma, cannabis use and migration were linked to fewer years of education. There was also a tendency for neurotrauma, urbanicity and cannabis use to be associated with fewer years in education.

However, the most striking findings were observed when the team compared patients without risk factor exposure to those with one to four or more environmental risks, with each additional risk factor worsening the outcome.

Schizophrenia symptoms appeared 8 years earlier in patients with four or more risk factors than in those with none, while prodrome appeared 9 years earlier. And having four or more risk factors was associated with 3 years less time spent in education, 39.5% more unemployment and 1.2 more hospital admissions, on average, when compared with having no risk factors.

Notably, cannabis use alone explained 10.2% of the variance in age at disease onset, compared with 4.7% explained by all other environmental risks together.

Since cannabis use is a preventable risk factor, “[t]his result calls for public education that targets prevention”, say they 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”.

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