Anorexia nervosa in Monozygotic Twins

Which is more important, hereditary factors or psychological environment factors, in the etiology of anorexia nervosa? The question is studied by considering 7 cases of anorexia nervosa in monozygotic twins of the authors’ own practice. In 5 of 7 cases, only 1 of a set of twins was found to be suffering from anorexia nervosa. On the other hand, in 2 of 7 cases, both twins were diagnosed as having anorexia nervosa. Even in the concordant cases studied by the authors, however, the quality or degree of anorexia nervosa in each case was different. Therefore, even given the existence of concordant cases, without inquiring precisely into the quality or degree of anorexia nervosa, it is not possible to conclude that hereditary factors play a determining role in the etiology of anorexia nervosa.