Greater occurrence of schizophrenia in dizygotic but not monozygotic twins. Register-based study.

Abstract

A previous study demonstrated a higher rate of first hospitalisation for schizophrenia in twins than in singletons. To compare the schizophrenia rates in monozygotic twins, dizygotic twins and the general population. Through record linkage between the Young Cohort of the Danish Twin Register and the Danish Psychiatric Case Register, the rate of schizophrenia in monozygotic and dizygotic twins and the rate in the general population were compared. The rate of first admission to hospital for schizophrenia in dizygotic twins was 40% greater than that in the general population. The rate in monozygotic twins was not increased. The difference between the rates in mono- and dizygotic twins was statistically significant (P < 0.001). This result is surprising and is in the direction opposite to that expected, suggesting new possibilities in the study of risk factors.