TESTING THE EFFECT OF SEASON OF BIRTH ON FAMILIAL RISK FOR SCHIZOPHRENIA AND RELATED DISORDERS

Background. An excess of late winter and early spring births in schizo phrenia has been repeatedly demonstrated. Previous evidence has sugges ted that the risk for schizophrenia may differ in relatives of schizop hrenic probands born in this high risk period v. at other times of the year. Method. In an epidemiologically based family study conducted in the west of Ireland, we examined the relationship between season of b irth in schizophrenia and schizophrenia spectrum probands and the risk for schizophrenia and related disorders in first-degree relatives. Ri sk was assessed using the Cox proportional hazard method. We examined four birth seasons previously shown to significantly predict risk for schizophrenia. Results. Neither the risk for schizophrenia nor that fo r schizophrenia spectrum disorders in relatives was significantly asso ciated with season of birth in probands. Conclusions. Season of birth does not, in this sample, identify schizophrenic probands with particu larly high or low familial vulnerability to illness.