Mental illness in the biological and adoptive families of adopted individuals who have become schizophrenic.

In a sample of 5483 adults who had been legally adopted early in life by persons not biologically related to them, 33 were identified, from mental hospital records for whom a diagnosis of definite schizophrenia (chronic, latent, or acute) could be agreed upon by four raters. An equal number of matched controls were selected from the sample of adopted individuals who had never been admitted to a mental hospital. Ninety percent of the living parents, siblings, and half-siblings, biological and adoptive, cooperated in an extensive psychiatric interview permitting a consensus diagnosis by three blind raters. Schizophrenia and uncertain schizophrenia were found to be significantly concentrated in the population genetically related to the schizophrenic adoptees. Their adoptive relatives did not differ from the control populations in the prevalence of schizophrenic illness.