Compared to the general population, siblings of patients with schizophrenia have a higher risk of developing schizophrenia.

This study analyzed population-based data to examine the risk of hospitalization for schizophrenia and affective disorders among full vs. half siblings of patients with schizophrenia, and among persons with 1 or more siblings with schizophrenia vs. those with 2 or more.

This study assessed the familial influence of schizophrenia on the development of schizophrenia and other mental disorders in siblings.

The full (n = 12,555) and half (n = 2,707) siblings of 6,115 patients with schizophrenia (ICD F20.0–20.9) were identified from the Israeli Psychiatric Hospitalization Registry. Age and gender matched controls (n = 61,048) were identified from the Israeli Population Registry. The sample's psychiatric hospitalizations were recorded from the registry.

Compared to controls, risk for schizophrenia was higher among persons with one or more (OR = 9.36, 95%CI: 7.73–11.33) or 2 or more (OR = 13.76, 95%CI: 8.84–24.15) full siblings with schizophrenia. Similarly, persons with one or more (OR = 7.91, 95%CI: 5.15–12.14) or 2 or more (OR = 8.44, 95%CI: 3.57–19.94) half siblings with schizophrenia had a higher risk of schizophrenia. Similarly, risk for hospitalization for affective disorders was higher among persons with one or more (OR = 7.29 95%CI: 5.60–9.49) or 2 or more (OR = 10.25, 95%CI: 5.50–19.10) full siblings with schizophrenia.

This population-based study strengthens existing knowledge that schizophrenia has a strong familial, perhaps genetic component; and the greater the familial load, the greater the risk. Familial schizophrenia also increases risk for affective disorders, emphasizing the overlap between these disorders.