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A nationwide Finnish sample of schizophrenic mothers' offspring given up for adoption was compared blindly with matched controls (i.e., adopted-away offspring of nonschizophrenic biological parents). The offspring were born 1927-79. To date, a total of 247 adoptive families (112 index and 135 controls) have been investigated and rated. Of the 10 psychotic cases, 8 are offspring of schizophrenics and 2 are control offspring. However, no seriously disturbed offspring is found in a healthy or mildly disturbed adoptive family, and of those offspring who were psychotic or seriously disturbed, nearly all were reared in disturbed adoptive families. This supports the hypothesis that a possible genetic vulnerability has interacted with the adoptive rearing environment.
Tienari et al. (Thu,) studied this question.