Dyslexia, handedness and syndromes of psychosis-proneness.

In an earlier study, adult dyslexia was found to be strongly associated with positive schizotypal traits, and particularly with unusual perceptual experiences. However, recent evidence suggests that the structure of psychosis-proneness in normals may involve three or four distinct yet related dimensions. Therefore a further study was conducted, using a wider range of measures, to explore associations between dyslexia and these different syndromes of psychosis-proneness. Relationships with handedness were also investigated. If three syndromes of psychosis-proneness were delineated, broadly corresponding to "Active", "Withdrawn" and "Schneiderian/Unreality" syndromes of schizophrenia, dyslexics showed elevations on both positive syndromes (Active and Unreality), but not on the negative, Withdrawn syndrome. With a four-factor model only one dimension, perceptual/cognitive anomalies, distinguished dyslexics from controls. These findings confirm an association between dyslexia and positive, but not negative, schizotypal traits. Mixed-handedness was strongly associated with dyslexia, and in controls with those measures of psychosis-proneness involving unusual perceptual experiences. This suggests that reduced lateralization may be a feature common to both dyslexia and the Unreality syndrome of schizotypy, which may help to account for the strong relationship between them.