Non-genetic pathologic developments of brain-wave patterns in MZ twins

Evidence from previous studies has suggested that the inter-individual differences of human brain-wave patterns (EEG) are predominantly determined by genetic factors, and that the EEG maturation is under strict genetic control. Yet investigations into monozygotic (MZ) twins discordant and concordant for schizophrenia yielded a reduced within-pair EEG concordance as compared to healthy control twins, and the severity of illness, as derived from EEG-differences between affected and unaffected individuals, was closely related to the severity of illness as provided by psychopathology scores and axis-V overall social functioning. Consequently, EEG abnormalities associated with schizophrenia and manifested differently in the co-twins concordant for schizophrenia were hypothesized to reflect nongenetic, pathologic developments of genetically identical brains. Little is known about the "normal" range of EEG variation throughout the process of brain maturation. Our study of 337 healthy, adolescent twin pairs with repeated assessments at 3-year intervals, together with EEG recordings of their parents, aimed to determine normative data with respect to EEG maturation and the developmental synchronies in MZ and DZ (dizygotic) twins during adolescence. It turned out that the within-pair EEG similarity in MZ/DZ twins was, at each stage of development, identical in magnitude to that of adult MZ/DZ twins, while the parent-offspring EEG similarity during adolescence was significantly lower than that seen with adult offspring.