The clinical and etiological relation between autism spectrum disorders (ASD) and schizophrenia is unclear. The degree to which these disorders share a basis in etiology has important implications for clinicians, researchers, and those affected. Our objective was to determine if a family history of schizophrenia and/or bipolar disorder was a risk factor for ASD. We conducted a case-control evaluation of histories of schizophrenia or bipolar disorder in first-degree relatives of probands in three samples, population registers in Sweden, Stockholm County, and Israel. Probands met criteria for ASD, and affection status of parents and siblings for schizophrenia and bipolar disorder were established
