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 If three syndromes of psychosis-proneness were delineated, broadly corresponding to "Active", "Withdrawn" and "Schneiderian/Unreality" syndromes of schizophrenia, dyslexics showed elevations on both positive syndromes (Active and Unreality), but not on the negative, Withdrawn syndrome.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.