Schizophrenia or bipolar disorder in first-degree relatives, such as parents or siblings, may be associated with increased risk of autism spectrum disorder (ASD), according to a report published Online First by Archives of General Psychiatry, a JAMA Network publication.

Patrick F. Sullivan, M.D., F.R.A.N.Z.C.P, of the University of North Carolina at Chapel Hill, and colleagues used population registers in Sweden and Israel to examine whether a family history of schizophrenia, bipolar disorder, or both were risk factors for ASD, a group of developmental brain disorders.

The clinical and etiologic relationship between ASDs and schizophrenia is unknown, and bipolar disorder was included given its overlap with schizophrenia, according to the study background.

Researchers conducted a case-control evaluation of histories of schizophrenia or bipolar disorder in first-degree relatives of probands from three group samples: two in Sweden and a third of conscripts (recruits to military service) in Israel.

The presence of schizophrenia in parents was associated with an increased risk for ASD in a Swedish national group sample (odds ratio [OR], 2.9) and a Stockholm County, Sweden, group (OR, 2.9), study results show. Schizophrenia in a sibling also was associated with an increased risk for ASD in the Swedish national group (OR, 2.6) and the Israeli conscription group (OR, 12.1). Bipolar disorder showed a similar pattern of association but of a lesser magnitude, the results indicate.

"Our findings indicate that ASD, schizophrenia and bipolar disorders share etiologic risk factors. We suggest that future research could usefully attempt to discern risk factors common to these disorders," the authors comment.

The Swedish Council for Working Life and Social Research, the Swedish Research Council and the Beatrice and Samuel A. Seaver Foundation funded this study.