[quote Ereshkigalangcleg]The present study searches to find neural correlates for the respective conditions, using fractional anisotropy (FA) as a measure of white matter connections that has consistently shown sex differences. We compared FA in 40 transgender men (female birth-assigned sex) and 27 transgender women (male birth-assigned sex), with both homosexual (29 male, 30 female) and heterosexual (40 male, 40 female) cisgender controls. Previously reported sex differences in FA were reproduced in cis-heterosexual groups, but were not found among the cis-homosexual groups. After controlling for sexual orientation, the transgender groups showed sex-typical FA-values. The only exception was the right inferior fronto-occipital tract, connecting parietal and frontal brain areas that mediate own body perception.
[[https://www.nature.com/articles/s41598-017-17352-8]][/quote]
I'll complete the abstract here as a couple of sentences were missing from the end of yours:
"After controlling for sexual orientation, the transgender groups showed sex-typical FA-values. The only exception was the right inferior fronto-occipital tract, connecting parietal and frontal brain areas that mediate own body perception. Our findings suggest that the neuroanatomical signature of transgenderism is related to brain areas processing the perception of self and body ownership, whereas homosexuality seems to be associated with less cerebral sexual differentiation.
And an extract from the discussion of this paper which is interesting:
"Importantly, the present data also provide a neuroanatomical underpinning for a GD/transgender-specific aspect - the body dysphoria and great distress due to incongruence between physical sex and experienced gender. The right-hemispheric differences between cis-homosexual and transgender groups, together with the confirmed aberration of FA in the (right) IFOF, provide compelling indications for the hypothesized different own body perception, specifically in transgender individuals. In line with our results, several previous neuroimaging studies found differences between trans- and cisgender groups particularly located in the right hemisphere16,17,22,27,29, more specifically in the right insula, (pre-) cuneus, temporo-parietal junction, orbito-frontal, medial frontal, and anterior cingulate cortex. These regions, and the right hemisphere in general have been reported to be involved in cognitive processes of (body) perception in relation to self, body ownership, ego-centric representation, and bodily self-consciousness "
So from what I can see here, these researchers have found little in the way of overall brain differences after they have controlled for sexual orientation, but they do feel they have found one clear difference; a neuroanatomical signature area for transgenderism in brain regions to do with processing perceptions of self and body ownership. Which suggests a biological underpinning to sense of gender identity and distress at gender incongruence.
A lot of the studies are so small, there's a lot of work to be done and getting large enough numbers to participate is likely to be a problem .