When the proband had bipolar disorder, there was a markedly increased risk for a diagnosis of schizophrenia among their first degree relatives. The risk was 2.4 (2.1–2.6) for parent-offspring and 3.9 (3.4–4.4) for full sibling relationships. Half-siblings also had an increased risk. When adoptive parents had a diagnosis of bipolar disease, the relative risk for the adoptees to have a diagnosis of schizophrenia was 1.5 (0.7–3.5). Similar results were found when we investigated the risk for bipolar disorder in relatives of probands with schizophrenia (last column of Table 2). There were no noticeable sex-differences in the familial risks (data not shown).
