I respectfully disagree.
Women have two X chromosomes, men have one X and one Y. There is information on "extra" leg of the 2nd X chromosome that is "missing" on the Y chromosome, and that determines the sex of the child. I think we'd both agree thus far.
Now, what if that same information was "missing" from the extra leg of the 2nd X chromosome? We already know that the gender gene isn't the only information on that extra leg - it's how women can be carriers of some genetic diseases but not be afflicted themselves. So, it's entirely possible that the information could be missing from the second X chromosome as well.
Then you are a mutant. But that is not the issue in this case. If someone thinks they are a different gender than their chromosomes imply, then they are not "transgendered", but seriously mentally ill. If you think otherwise, then you should start a thread on Jada Pinkett Smith.