The inheritance of schizophrenia spectrum disorders: a reanalysis of the Danish adoptee study data

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Abstract
The frequency of schizophrenia spectrum disorders in 2 groups of persons adopted in infancy or early childhood, those with a psychotic parent (index group) and those whose biological parents had never had a psychiatric diagnosis or treatment (control group), were compared. They found significantly more disorder in the index group. Reanalysis of the original material using DSM-III [Diagnostic and Statistical Manual of Mental Disorders, III] and stricter exclusionary criteria applied to the parents yielded 3 times as many schizophrenia spectrum disorders in the index as in the control groups. This difference remained statistically significant, supporting the operation of genetic factors in the transmission of the traits comprising the schizophrenic spectrum of disorders.