Sex is determined by one's chromosomes. XX = Female, XY = Male. There are rare cases of genetic diseases where individuals have some other chromosomal makeup and there are rare cases of hermaphrodism where the expression of sex characteristics goes awry. We used to call things like these "birth defects" and they were always handled as rare medical conditions.
I have followed the thread as it progressed this morning and considered the misnomer transgender.
I finally concluded there is no word in the language to describe something that doesn’t exist.
Pretender is a better word. He is a pretender, assuming feminine characteristics and mannerisms