SINGLE INDICATOR OF RISK FOR SCHIZOPHRENIA - PROBABLE FACT OR LIKELY MYTH

The longitudinal followup strategy in high-risk research is being incr easingly complemented by the use of psychosis-proneness scales to sele ct subjects for study who might be vulnerable to schizophrenia and who show differences on laboratory measures that could act as endophenoty pic markers for use in genetic investigations. Three types of experime ntal paradigm have been adopted, drawn from cognitive psychology, psyc hophysiology, and the neuropsychology of hemisphere function. Results adopting each of these approaches are examined, alongside recent facto r-analytic evidence that psychosis-proneness scales currently in use t ap up to four different components that map onto the clinical heteroge neity of schizophrenia (and possibly other forms of psychosis). No one of these components clearly emerges as, or points to, a single indica tor of risk, though some aspect of neurocognitive functioning seems a likely candidate. Even so, it is argued, the clinical expression of vu lnerability must be due to a convergence in an individual of several c omponents of risk since individually (and notably so for ''susceptibil ity to positive symptoms'') they are very common in the healthy popula tion. In evaluating the evidence, attention is drawn to two crucially different ways that investigators in schizophrenia research have const rued the notion of continuity (1) as subclinical defect (or forme frus te of disease) having varying expression or (2) as biologically based personality dimensions that simultaneously describe the dispositions t o aberrations of function leading to degree of illness. It is noted th at the model of continuity chosen can significantly shape the way the results of risk research are interpreted and the theories of psychosis to which they give rise.