Suicide attempts in a national population of twins concordant for psychoses.

Psychotic disorders are associated with an increased risk of suicide attempts, the etiology of which remains unknown across diagnoses. Thus it is relevant to understand how genetic and environmental factors contribute to the liability of suicide attempts in psychosis. The current study aims to examine the role of genetic and environmental factors in suicide attempts across psychotic disorders in twins concordant for psychosis. The study population consisted of all twin pairs in the Israeli National Psychiatric Case Registry hospitalized with a last discharge diagnosis of a psychotic disorder. Twin pairs (N=116) were born between 1900 and 1993 and hospitalized from 1964 to 2001. Competing genetic models were examined to decompose the variance in suicide attempts into: the individual-specific environment (unique), shared-family environment, and genetic effects. Across schizophrenia, psychosis and non-affective psychosis comparison of genetic models showed a model combining shared-family and unique environmental effects were superior to competing genetic models. Modeling estimates for attempted suicide were: in non-affective psychosis 60% to the shared-family and 40% to the unique environment; in schizophrenia 60% to the shared-family and 40% to the unique environment; and in psychosis 66% to the shared-family and 34% to the unique environment. Across psychosis, schizophrenia and non-affective psychosis vulnerability toward suicide attempts consists predominantly of substantial individual and familial environmental elements.