Sub-clinical psychosis symptoms in young adults are risk factors for subsequent common mental disorders.

BACKGROUND: Not all persons identified in the early stages to be at risk for psychosis eventually cross the threshold for a psychotic illness. However, sub-clinical symptoms may not only indicate a specific risk but also suggest a more general, underlying psychopathology that predisposes one to various common mental disorders.
METHODS: Analyzing data from the prospective Zurich Cohort Study, we used two psychosis subscales - "schizotypal signs" and "schizophrenia nuclear symptoms" - derived from the SCL-90-R checklist that measured sub-clinical psychosis symptoms in 1979. We also assessed 10 different diagnoses of common mental disorders through seven interview waves between 1979 and 2008. This 30-year span, covering participant ages of 19/20 to 49/50, encompasses the period of highest risk for the occurrence of such disorders.
RESULTS: Both psychosis scales from 1979, but especially "schizotypal signs", were significantly correlated with most mental disorders over the subsequent test period. Higher values on both subscales were associated with an increasing number of co-occurring disorders.
CONCLUSIONS: Our data demonstrate that sub-clinical psychosis generally represents a risk factor for the development of common mental disorders and a liability for co-occurring disorders. This refers in particular to dysthymia, bipolar disorder, social phobia, and obsessive-compulsive disorder. Proneness to psychosis could signal a fundamental tendency toward common mental disorders.