Effects of Family History and Place and Season of Birth on the Risk of Schizophrenia

Twin and adoption studies strongly suggest that genetic transmission accounts for most of the familial aggregation of schizophrenia. 1 , 2 However, little is known about the contribution of familial aggregation to the occurrence of schizophrenia in the general population and the mode of inheritance of the disease. Environmental risk factors have also been suggested, including maternal obstetrical complications, 3 , 4 influenza infection during the mother's pregnancy, 5 season of birth, 6 urban place of birth or upbringing, 7 and low social class. 8 Questions about the relative importance of genetic and environmental risk factors for mental disorders, as well as their possible interaction, remain to be . . .