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A nationwide Finnish sample of schizophrenics' offspring given up for adoption was compared blindly with matched controls, that is, adopted-away offspring of nonschizophrenic biologic parents. The adoptive families were investigated thoroughly by joint and individual interviews and psychologic tests. Biologic parents were also interviewed and tested. Among the 144 index and 178 control offspring, the percentage of both psychoses and other severe diagnoses (borderline syndrome and severe personality disorder) was significantly higher in the index adoptees than in the matched control adoptees. Of the 15 psychotic adoptees in the total sample to date, 13 are offspring of schizophrenics and 2 are control offspring. Both global clinical ratings and test data for the adoptive, rearing parents also correlate with the symptomatic status of the adoptees. A prospective, longitudinal study of adoptees at risk is being undertaken to explore the direction of effects between adoptees and adoptive parents.
Pekka Tienari (1991) studied this question.