“The brain-sex theory of transsexualism has never been easy to reconcile with clinical reality: Homosexual and nonhomosexual MtF transsexualism are so different clinically that it is almost impossible to imagine that they could have the same etiology. Nevertheless, for a time the Zhou/Kruijver data gave the brain-sex theory a certain superficial plausibility. In 2002, Chung et al. reported new data that raised serious doubts about the brain-sex theory, but the authors were able to explain why the theory might still be plausible. The new data reported by Hulshoff Pol et al. in 2006 did not invalidate these explanations, but it rendered them largely irrelevant. The simplest and most plausible explanation of the Zhou/Kruijver findings is that they are attributable, completely or predominantly, to the effects of cross-sex hormone therapy administered during adulthood. There is no longer any reason to postulate anything more complicated.
The brain-sex theory was never helpful in explaining clinical observations; now it has become irrelevant to explaining neuroanatomical observations. It is time to abandon the brain-sex theory of transsexualism and to adopt a more plausible and clinically relevant theory in its place.”