>>40511499A lot of things. Like clusters of certain important cells thought to relate to body identify formation that develop in the fetus like the opposite sex, like structural connections in the brain more similar to the opposite sex even in pre-hrt children, and many other signs of switched development driving hormones in the womb. All of which corresponds with classic trans reports of early identification, behaviors, and interests closer to the opposite sex, and justifying body and mind incongruences.
At best you can say that they're feminized men and masculinized women, but you can't deny it, and can't fix it since that development is done already. Even if you want to stick to that story you would still be better off saying it only applies to a rare group. John Money tried to socially brainwash a boy with a botched circumcision into believing he was a girl since age 2. It didn't work out, he figured it out and killed himself as an adult, he just didn't have that same development as a fetus.