Johns Hopkins University distinguished professor of psychiatry and behavioral sciences Paul McHugh has an answer. Gender dysphoria is an “overvalued idea” or ruling passion. This is “an idea held by many people in the world, but held intensely by the patient or the person, who is making a life of that idea,” Dr. McHugh told me. Many people believe that it is good to be thin, for instance. Many adolescent girls believe it’s better to be a boy. But for anorexics and those with gender dysphoria, those ideas become all-consuming.

