Psychosis risk factors have limited predictive power

Jan 24 2014

By Eleanor McDermid, Senior medwireNews Reporter

Factors known to be linked to schizophrenia risk have little predictive power at either the individual or population level, report researchers.

Also, variables with the largest impact at the population level had only a very small impact on individual risk, and vice versa, their study findings suggest.

For the study, which involved more than 2 million Danish residents identified from national registers, Holger Sørensen (University Hospital of Copenhagen, Denmark) and co-workers examined the impact of five psychosis risk factors: parental history of psychiatric illness, being born in an urban area, advanced parental age at birth, loss of a parent, and being a second-generation immigrant.

The highest incidence of schizophrenia occurred among people whose parents were both schizophrenic, at an incidence rate ratio (IRR) of 20.96, after accounting for age, gender, and their interaction, calendar year, and all other studied psychosis risk factors. But the population-attributable risk (PAR) was just 0.12%.

“[O]ur findings illustrate that the predictive power on the individual level is far from any level that would be clinically useful,” the researchers write in Schizophrenia Research. “Thus, the variables with the highest predictive power (both parents diagnosed with schizophrenia) have very limited impact on the total population morbidity.”

The factor with the largest PAR was urban birth, specifically being born in the capital city, with a PAR of 11.73%. But the individual risk associated with this factor was small, with an IRR of just 1.80. Being born in the suburbs of the capital city, or a provincial city or town, had smaller but still significant effects on both PAR and individual risk.

“We were not able to identify an environmental (non-genetic) risk factor that can compete in magnitude with genetic factors, as far as individual predictive power is concerned,” report the researchers.

IRRs associated with a parental history of mental illness ranged from 2.07 for having one parent with a history of psychiatric services contact to 6.60 for one parent and 20.96 for both parents being schizophrenic. But all other studied factors, although statistically significant, had IRRs of less than 2.0.

“Obviously our study did by no means cover all potentially relevant risk factors,” says the team. “Hence, one could also hope that for example genetic data or other biomarkers would enhance the ability to predict disease.

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