There were some early studies that seemed to show brains of the trans-identifying are atypical for their sex, and perhaps closer to the opposite sex in some mea

There were some early studies that seemed to show brains of the trans-identifying are atypical for their sex, and perhaps closer to the opposite sex in some measurements, but these didn't control for sexuality, and many used exclusively homosexual cohorts. It turned out that these were brain differences relating to homosexuality. Later studies that controlled for sexuality (that is, by including both same-sex and opposite-sex attracted transsexuals in the cohort) couldn't replicate the earlier findings of sexually dimorphic brain structures being associated with transsexuality itself. Instead, researchers found functional differences in brain regions associated with bodily perception, similar to what is seen in body dysmorphic disorder (BDD) patients. Which I think is a more interesting finding, perhaps suggesting that gender dysphoria is a subtype of BDD, or at least has some neurological commonality.