Pathology

Consider that gender variance became mental pathology only over the last 40 years or so. Before that it was either celebrated by native cultures or at worst seen as a mild aberration or moral failing in the West. Heck, even European royalty practiced it and there are countless historical examples too numerous to mention here. Even the first version of the DSM was only published in 1952.

At the turn of the 20th century a gay man called Magnus Hirschfeld (German physician and sexologist) began to formalize the subject matter and treat patients with varying degrees of gender disconnect including Lili Elbe. The Nazis took care of his lab and burned his books and eventually sent many LGBT people to the gas chambers as they tended to stain their Aryan purity model.

Later enter Kurt Freund (no doubt infected by the Nazi ideology) and his penile erection test to root out homosexuals bound for the Czech army who eventually ends up at the CAMH in Toronto and in turn infects Ray Blanchard.

In the US, thankfully Harry Benjamin (with much grace and panache) picked up the torch from Hirschfeld and wrote what I still consider to be one of the definitive books on the subject matter.