Background
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.
Findings
The presence of schizophrenia in parents was associated with an increased risk for ASD in a Swedish national cohort (odds ratio 2.9, 95% CI 2.5–3.4) and in a Stockholm County cohort (odds ratio 2.9, 95% CI 2.0–4.1). Similarly, schizophrenia in a sibling was associated with an increased risk for ASD in a Swedish national cohort (odds ratio 2.6, 95% CI 2.0–3.2) and in an Israeli conscription cohort (odds ratio 12.1, 95% CI 4.5–32). Bipolar disorder showed a similar pattern of associations but of lesser magnitude.
Interpretation
Findings from these three registers along with consistent findings from a similar study in Denmark suggest that ASD, schizophrenia, and bipolar disorder share common etiological factors.
Funding
Swedish Council for Working Life and Social Research, the Swedish Research Council, and the Beatrice and Samuel A. Seaver Foundation.