Normal personality characteristics in identical twins discordant for schizophrenia.

The authors examined normal personality characteristics of monozygotic (MZ) twins discordant for schizophrenia. Twenty pairs of discordant twins were analyzed; 11 pairs of MZ twins concordant for schizophrenia served as a comparison group. Personality was assessed using the Multidimensional Personality Questionnaire (MPQ; A. Tellegen, 1995). Among discordant twin pairs, twins with schizophrenia were more deviant than normal co-twins on all but 4 of the MPQ's scales. Analysis of MZ twin correlations among the discordant twin pairs revealed substantial erosion of personality similarity as compared to normal individuals, although a cluster of scales related to Constraint/Psychoticism showed significant correlations. The results highlight striking personality divergence related to nonshared environmental influences. It is not possible to determine the point at which the twins diverged, although previous findings from this sample suggest that the observed personality differences may reflect effects of schizophrenia on normal personality.