Critique of the Danish-American studies of the adopted-away offspring of schizophrenic parents.

Studies of the adopted-away children of schizophrenic parents that have claimed to have shown a strong genetic factor in the etiology of schizophrenia have had a great impact on psychiatry, including effects on the direction and support of research. An examination of these studies, however, controverts these conclusions. The authors demonstrate that without the inclusion of parents with manic-depressive and indefinite diagnoses in the index group, there is no statistically significant difference between the number of offspring with schizophrenic spectrum diagnoses in the index and control groups.