Schizophrenia in Twins and the Diffuse Ego Boundary Hypothesis

In a sample of 31,818 male veteran twins, 1.14 percent were found to be schizophrenic. This incidence of schizophrenia is similar to that in the general population, suggesting that there is no clear difference in incidence of schizophrenia between twins and nontwins. The incidence of schizophrenia in monozygotic twins in this sample was no greater than in dizygotic twins; this accords with the results of four other major twin studies. Thus the data do not support the hypothesis that greater diffusion of ego boundaries and confusion of identity occur in twins, or especially "identical" (MZ) twins, or is significant in the occurrence of schizophrenia in twins. Neither, however, do they refute it, Since compensating factors may be present.