The EEGs of twenty-five pairs of twins, one or both of whom were mentally retarded, were studied. The concordance rate for mental retardation in monozygotic twins was higher than that in dizygotic twins. The vast majority of cases of mental retardation were considered to be caused by genotype but some exogenous causes were observed in discordant monozygotic twins.
Paroxysmal discharges in the EEG especially those of centrencephalic type were suspected to be bio-electrical expressions of a transmissible cerebral susceptibility which may easily lead to intellectual deterioration by brain damage or epilepsy.
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