The Harry Benjamin Syndrome 2: The Scientific Basis
"In male-to-female subjects the number of neurons in the INAH3 does not seem to be related to sexual orientation, nor to the onset time of transsexuality, but rather to atypical early female-biased gender."
The researchers do open up for a discussion of subtypes of transsexual people, but note that it was impossible to do this in this study as most of the subjects were "non-homosexualearly onset male-to-female transsexual people". In this context "non-homosexual" means female oriented.
Images from Some Like it Hot from 1959, with Marilyn Monroe and Tony Curtis and Jack Lemmon in drag.
A slightly different version of this article was originally posted over at the Crossdreamer blog.