Implications of Adoption Studies on Schizophrenia

It is accepted that schizophrenia runs in families, but whether this relates to genetic or psychosocial transmission is an unanswered question. Kendler (1988) has articulated four testable hypotheses: (a) a general liability to any psychiatric illness (b) a liability to schizotypal functioning — oddness, suspiciousness etc. (c) a liability to broadly defined schizophrenic psychosis, or any functional, non-affective psychosis and (d) a specific liability to narrowly defined schizophrenia, e.g. using DSM-III-R criteria (American Psychiatric Association, 1987). Kendler suggests that neither hypothesis (a) nor (d) is correct, and that the familial predisposition is neither completely non-specific nor highly specific; available results strongly support the second hypothesis and also provide some support in favour of the third.