Well, I find this topic very interesting because when I was 14 and caught crossdressing I was put in a mental institution for six weeks.
At that time (1972) I know that DSM-II still listed homosexuality as a mental disorder, and may have done so for gender dysphoria
(or whatever term they may have coined for it then). Of course, I wasn't "mentally ill" when I was in there. That happened long afterwards... 😉