Environment plays primary role in psychosis transition

By Lucy Piper, Senior medwireNews Reporter

Research suggests that exposure to environmental risk factors may be necessary for individuals at genetically high risk for psychosis to transition from good health to the psychiatric disorder.

The study authors found that most transitions in individuals with a higher than average genetic risk for psychosis could be attributed to “powerful” environmental effects.

“The findings suggest that the rate of exposure to any environmental risk in the population is very high, or semi-ubiquitous, and transition from health to psychotic disorder is strongly dependent on such exposure,” say lead researcher Jim van Os (Maastricht University Medical Centre, the Netherlands) and colleagues.

Indeed, they found that the majority (68%) of 810 individuals at high genetic risk for psychosis (due to having a sibling with non-affective psychotic disorder) had been exposed to at least one of four environmental risk factors: childhood trauma, cannabis use, being in an ethnic minority group, or urban birth.

The rate of exposure was similarly high, at 60%, among 462 individuals at average risk for psychosis.

High-risk individuals were 2.2 times more likely to transition to psychosis than those of average risk, at a rate of 1.1% versus 0.4%.

But all transitions were associated with environmental exposure, irrespective of whether they occurred in those at high or average risk.

By contrast, 65% of patients who did not transition to psychosis were exposed to environmental risk factors, reflecting a significant difference.

Childhood trauma had the greatest effect on transition to psychosis, increasing the risk 34.4-fold, followed by cannabis use, minority ethnic group, and urban birth, which increased the risk 3.7- to 4.1-fold.

The proportion of transitions in the participants attributable to environmental risk ranged from 28% for minority ethnic group to 86% for childhood trauma, while 50% were attributed to genetic risk.

Nine of the 11 patients who transitioned to psychosis were exposed to both genetic and environmental risk, giving a rate of 82%, compared with 43% of patients who did not transition to psychosis.

“This finding suggests that exposure to both genetic and environmental risk factors is necessary for transition, which is compatible with underlying gene-environment interaction,” van Os and colleagues comment.

They note that exposure to environmental risk was not altered by genetic high risk status and there was no gene–environment correlation.

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