The Finnish adoptive family study of schizophrenia.

A nationwide Finnish sample of schizophrenic mothers' offspring given up for adoption has been compared blindly with matched controls; i.e., adopted-away offspring of non-schizophrenic biologic parents. The families have been investigated thoroughly by joint and individual interviews and psychological tests. In the 91 pairs where both the index and control families have already been investigated and rated, the total number of severe diagnoses (psychosis, borderline, character disorder) is 28.6 percent (26/91) in the index group and 16.5 percent (15/91) in the matched control group. Of the seven psychotic cases, six are offspring of schizophrenics and only one is a control offspring. However, no seriously disturbed offspring has been found in a healthy or mildly disturbed adoptive family, and those offspring who were psychotic and seriously disturbed were nearly all reared in disturbed adoptive families. This combination of findings supports the hypothesis that a possible genetic vulnerability has interacted with the adoptive rearing environment.