If you look at MRIs of human brains, you can determine the sex with pretty high accuracy. Researchers have even trained machine learning algorithms to differentiate with >90% accuracy.[1]

Researchers have tried this on transgender brains and come up with mostly noise. When they do find differences, it appears that the brains of trans-women are unlike cis-women. Ditto for trans-men.[2]

I am very confident that there is a ton of publication bias in any transgender research. If you publish a politically incorrect result, you risk your career.

1. https://www.ncbi.nlm.nih.gov/pubmed/30430711

2. https://www.researchgate.net/publication/337026445_Predictiv...