J Psychiatr Res. 2010 Jun 8. [Epub ahead of print]
http://www.ncbi.nlm.nih.gov/pubmed/20562024
Rametti G, Carrillo B, Gómez-Gil E, Junque C, Segovia S, Gomez A, Guillamon A.
Clinical Institute of Neuroscience, Hospital Clinic i Provincial, Barcelona, Spain; Institute of Biomedical Research August Pi i Sunyer (IDIBAPS), Barcelona, Spain.
Abstract
BACKGROUND: Some gray and white matter regions of the brain are sexually dimorphic. The best MRI technique for identifying subtle differences in white matter is diffusion tensor imaging (DTI). The purpose of this paper is to investigate whether white matter patterns in female to male (FtM) transsexuals before commencing cross-sex hormone treatment are more similar to that of their biological sex or to that of their gender identity. METHOD: DTI was performed in 18 FtM transsexuals and 24 male and 19 female heterosexual controls scanned with a 3 T Trio Tim Magneton. Fractional anisotropy (FA) was performed on white matter fibers of the whole brain, which was spatially analyzed using Tract-Based Spatial Statistics. RESULTS: In controls, males have significantly higher FA values than females in the medial and posterior parts of the right superior longitudinal fasciculus (SLF), the forceps minor, and the corticospinal tract. Compared to control females, FtM showed higher FA values in posterior part of the right SLF, the forceps minor and corticospinal tract. Compared to control males, FtM showed only lower FA values in the corticospinal tract. CONCLUSIONS: Our results show that the white matter microstructure pattern in untreated FtM transsexuals is closer to the pattern of subjects who share their gender identity (males) than those who share their biological sex (females). Our results provide evidence for an inherent difference in the brain structure of FtM transsexuals. Copyright © 2010 Elsevier Ltd. All rights reserved.
PMID: 20562024 [PubMed – as supplied by publisher]
Women Born Transsexual 
July 3, 2010 at 12:10 pm
Hmm, so why did they specifically pick heterosexual women as the female comparison group? And what was the sexual orientation of the male controls? I’m not saying this is wrong up but it is suspiciously like some manipulated studies that have gone before, from different centers.
The thing is that in 2d:4d finger ratios (which are established by week 8 of embryonic development, when the brain is mid development), T->M have the same as butch lesbian or CAH women – a bit masculinised (ring finger a bit longer) compared to femme lesbian, bisexual or straight women, or T->F transsexual women, who all have first and ring fingers about equal in length. Most men have significantly longer ring fingers (although about 30% of men have equal finger lengths). Male homosexuality seems not reflected in finger ratio.
But when Zucker and co. decided to look at finger ratios they compared the F->M with heterosexual women, and declared a difference that does not exist. And they used the GID criteria for M->F and lost the difference previously found with approved-for-SRS women. Manipulated results…
So this might be a reflection of sexual orientation, not gender identity.
If it isn’t then, wow, they’ve got a diagnostic tool. Just a few hundred dollars for a brain scan… Or they could just listen to the patient.