Self-reported schizotypy and bipolar disorder: demonstration of a lack of specificity of the Kings Schizotypy Questionnaire

Previous studies have demonstrated that schizophrenia patients score highly on self-reported measures of schizotypy such as the Kings Schizotypy Questionnaire (KSQ), but relatively little is known about the specificity of these self-reported features to schizophrenia. We aimed to explore the specificity of schizotypal features to schizophrenia by measuring their prevalence in subjects with bipolar disorder. The Kings Schizotypy Questionnaire (KSQ) was administered to participants (n=92) in a sibling-pair genetic linkage study of bipolar disorder. Scores were compared with those of participants in a similarly designed, concurrent family study of schizophrenia (n=135) and psychiatrically well controls (n=263). The bipolar group had significantly more schizotypal features than controls but significantly less than schizophrenia patients. Whether a bipolar subject had experienced positive psychosis had no effect on his/her schizotypy score. We conclude that elevated self-reported schizotypy as measured by the KSQ is not specific to schizophrenia, and may be associated with functional psychosis in general. (C) 2003 Elsevier Science B.V. All rights reserved.