Concordance for bulimia nervosa in twins

27 pairs of twins with bulimia nervosa according to DSM-III-R were assessed concerning concordance for bulimia nervosa and other eating disorders. There were 6 monozygotic females, 1 monozygotic male, 15 dizygotic females and 5 dizygotic twins of opposite sex. The concordance rates for bulimia nervosa (83.3 versus 26.7%) and for any eating disorder according to DSM-III-R (83.3 versus 33.3%) were significantly higher for monozygotic, as compared to dizygotic females. 27 (54%) of 50 twins had a diagnosis of depression according to ICD-9 criteria, with a small difference between monozygotic (60%) and dizygotic (53%) twins of the same sex. According to our data, monozygotic bulimic twins appear to have an increased genetic-biological vulnerability for a mental or eating disorder. Possible effects of disturbances in the process of individuation and in the development of an autonomous self due to social consequences of their physical identity with the cotwin are discussed.