I've started to look at the article itself a little. For what you would expect to be such an important article, it has only been cited 26 times. Very influential or groundbreaking articles are generally cited several hundred times even after only a few years.
If you're experienced at all in scientific research, then you'll know that some citations count more than others. Most citations are probably just introduction citations that the article glosses over to give a general overview of whatever topic the article is covering.
When you see
The demand for health care services in the gender identity units of Andalusia and Catalonia during the period of 2000 to 2009
as an article that cited this source, you get the indication that it was just mentioned in passing, not that it was research that other scientists felt worth building upon.
My point is, how can you consider this article to be groundbreaking meaty research, when scientists that work in the field don't seem to.
I apologize that I only have access to the Abstracts, but here's an interesting one
IntroductionUntreated transsexuals have a brain cortical phenotype. Cross-sex hormone treatments are used to masculinize or feminize the bodies of female-to-male (FtMs) or male-to-female (MtFs) transsexuals, respectively.
AimA longitudinal design was conducted to investigate the effects of treatments on brain cortical thickness (CTh) of FtMs and MtFs.
MethodsThis study investigated 15 female-to-male (FtMs) and 14 male-to-female (MtFs) transsexuals prior and during at least six months of cross-sex hormone therapy treatment. Brain MRI imaging was performed in a 3-Tesla TIM-TRIO Siemens scanner. T1-weighted images were analyzed with FreeSurfer software to obtain CTh as well as subcortical volumetric values.
Main Outcome MeasuresChanges in brain CTh thickness and volumetry associated to changes in hormonal levels due to cross-sex hormone therapy.
ResultsAfter testosterone treatment, FtMs showed increases of CTh bilaterally in the postcentral gyrus and unilaterally in the inferior parietal, lingual, pericalcarine, and supramarginal areas of the left hemisphere and the rostral middle frontal and the cuneus region of the right hemisphere. There was a significant positive correlation between the serum testosterone and free testosterone index changes and CTh changes in parieto-temporo-occipital regions. In contrast, MtFs, after estrogens and antiandrogens treatment, showed a general decrease in CTh and subcortical volumetric measures and an increase in the volume of the ventricles.
ConclusionsTestosterone therapy increases CTh in FtMs. Thickening in cortical regions is associated to changes in testosterone levels. Estrogens and antiandrogens therapy in MtFs is associated to a decrease in the CTh that consequently induces an enlargement of the ventricular system. Zubiaurre-Elorza L, Junque C, Gomez-Gil E, and Guillamon A. Effects of cross-sex hormone treatment on cortical thickness in transsexual individuals. J Sex Med 2014;11:1248-1261.
So, there's some evidence that the hormone treatments themselves are going to cause differences in the brain. They know this possibility of course, that's why the article you linked searches for differences in mtf and ftm before hormone treatment. Now you have to wonder, though, any study that shows a difference in the brain structure, are those transexuals that have already started hormone treatment?
If they're not, what then? Now that we've established that hormones can effect changes in the brains, then is it possible that transexuals live lifestyles closer to that of their preferred sex that lead to higher levels of some hormones that lead to differences in the brain.
As I've already said, what would be really convincing to me, is if they scanned male brains, scanned female brains, found the differences, and then showed that those difference favor males in ftms and females in mtfs but they can't do that. All they seem to be able to do is to take a scattershot approach hoping to find differences.