[Transsexualism: a Brain Disorder that Begins to Known].

Transsexualism describes the condition when a person's psychological gender differs from his or her biological sex. People with gender identity disorder suffer persistently from this incongruence and they search hormonal and surgical sex reassignment to the desired anatomical sex. This review, from an ethical perspective, intends to give an overview of structural and functional neurobiological correlations of transsexualism and their course under cross-sex hormonal administration. Several studies demonstrate an increased functional connectivity between cortex regions reaffirming psychosocial distress of psychologicalbiological sex incongruity. Such distress can be ascribed to a disharmonic body image due to changes in the functional connectivity of the key components of body representation network. These brain alterations seem to imply a strategic mechanism dissociating bodily emotions from bodily images. For a number of sexually dimorphic brain structures or processes, signs of feminization or masculinization are observable in transsexual individuals, who during hormonal administration seem to partly further adjust to characteristics of the desired sex. These changes allow a reduction of psychosocial distress. However, a model leading to a ″gender affirmation″ does not solve the problem, since brain disorders causing it are not corrected. This is a serious medical ethics issue. Prejudices should be left aside. To know what happens in the brain of transsexuals is a medical need, both to define what is and what is not, and so to choose an adequate treatment, and to decide and guide legal actions.