I recall reading another case study on twins in which one became a crossdresser and the other not. Since both had the same genetics, the same hormonal experience in the womb and the same living conditions at home then the only sensible explanation is that transgenderness is based on nothing more than what type of personality you are born with, how this fits in with what society expects of you and whether you decide at some point during your childhood to stay true to yourself or whether you let gender conditioning castrate your feminine side.
Unfortunately for boys, the choice to stay true forces them into the dark closet where their transgendered personality gets corrupted and twisted by fantasies and new found sexuality, instead of being expressed as a normal personality trait in a welcoming social environment. The end result is a secretive shamed crossdresser who is not recognizable from his simple, humble beginnings as a healthy routine boy who just happens to like things which society, in its ignorant wisdom, has deemed taboo.
This tool we call crossdressing is based on nothing more than personality traits - our likes and dislikes - which become ingrained into our being as we grow up.
Imagine for a second you loved to eat strawberries as a child. But society said at age 10 you were now prohibited from eating them anymore. Is there not a likelihood that some people will find this rule silly? that everytime they see a strawberry the fact they are forbidden to eat it will grate against their consciousness? will some not eventually choose to ignore the rule and sneak into a strawberry field late at night when nobody can see them? And when they taste that strawberry, it will be amazing because of all the emotions that have been condensed into the thought of eating one.
I find it odder that people have to seek weird and wonderful theories to explain the fact that we desire a certain look for ourselves. This is just normal routine humanity folks! To me, this is like someone using hormone wash theory to explain why they like cars so much. Nobody needs theories to explain our love of cars so why do we need theories to explain our choice in clothes? This is just who we are, the only odd thing is why society is so intolerant of diversity among people.