EEG differences in monozygotic twins discordant and concordant for schizophrenia

In an EEG study of 91 healthy subjects with repeated assessments, 40 pairs of healthy MZ twins, 27 pairs of MZ twins discordant for schizophrenia, and 13 pairs of MZ twins concordant for schizophrenia, we investigated (1) the trait quality of brain-wave patterns with respect to inter-individual differences, intra-individual stability over time, and within-pair MZ coincidence, (2) the characteristics of brain-wave patterns that allow one to discriminate reliably between affected and unaffected individuals, and (3) the characteristics of brain- wave patterns that reflect the severity of illness. Most parameters chosen to quantify brain-wave characteristics were found to possess distinct trait-like qualities, as indicated by large inter-individual differences, great stability over time, and high within-pair coincidences in healthy MZ twins.

In comparison to healthy controls, MZ twins discordant and concordant for schizophrenia exhibited a much lower within- pair coincidence, although the majority of correlation coefficients differed significantly from zero. Accordingly, abnormalities of brain-wave patterns associated with schizophrenia and differently manifested in MZ co-twins concordant for schizophrenia seem to reflect non-genetic, idiosynchratic pathologic developments of genetically identical brains. These abnormalities allowed us to discriminate reproducibly between affected and unaffected individuals by means of a multivariate discriminant function with an overall accuracy of 80%.

The severity of illness, as derived from the brain-wave discriminant function, was closely related to the severity of illness provided by psychopathology scores and overall AXIS V social funtioning. In consequence, the non- genetic, highly individual pathologic development of brain- wave patterns in schizophrenia clearly limit the usefulness of these quantities as biological markers for investigations into the genetic predisposition to this illness.

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