Nearly all of them! If we could fine something wrong in the body it likely wouldn’t be considered a mental disorder. Anorexia nervosa for instance can’t necessarily be found in the brain, but lots of people still struggle with it. It’s understood by how people behave who have it. Sometimes, we will be able to locate things in the brain that are more likely to be present in someone with a certain disorder, but it’s always a mix of social and other things. Gender dysphoria or gender identity disorder (which is what I was diagnosed with) isn’t unique in this way. And we’re finding things in the brain for that too. It doesn’t mean that we were necessarily born like this, because brains are very plastic and can change a lot, but it is another indicator that it is a real thing. I feel like the only way your position makes sense is if you just say mental illnesses aren’t real to you.

https://www.eneuro.org/content/6/6/ENEURO.0183-19.2019