Background: Previous studies examining the relationship between psychopathological syndromes of the psychotic illness and familial liability to schizophrenia and mood disorders have obtained inconclusive results. The aim of this study is to further examine this issue by analyzing a large sample of psychotic probands and their first-degree relatives.
Methods: The sample was composed of 660 psychotic inpatients and their 2987 first-degree relatives. Probands were assessed for index episode and lifetime symptoms, while relatives were assessed for lifetime diagnosis of schizophrenia and major mood disorders. Associations between factor-analysis derived syndromes in probands and familial loading for schizophrenia and major mood disorders were tested.
Results: Familial morbid risk of schizophrenia was predicted by the negative syndrome in probands and familial morbid risk of mood disorders was predicted by mania, depression and catatonia syndromes in probands. This association pattern was relatively independent of type of symptom rating (index episode or lifetime) and probands' diagnosis of schizophrenia or major mood disorder. Familial loading for schizophrenia and mood disorders cut-across the DSM-IV categories of psychotic disorders in probands.
Conclusion: From a dimensional perspective, the negative syndrome is related to familial liability to develop schizophrenia. Mania, depression and catatonia syndromes are related to the familial liability to develop major mood disorders. Categories of psychotic disorders are on a continuum of familial liability to schizophrenia and major mood disorders.