And btw Steven, I googled ICD-10 and it was started in the 80s and finished in 1992. It's probably not that good a source to use since modern attitudes have changed many people's opinions on transgender individuals. I'm sure, if WHO had a website in the 40s, being gay would have been listed as a mental illness. Doesn't mean that it is imo.
Edit: I may be wrong with the dates btw. That's just what a quick google search threw up