Can you provide your definition of GID, because according to the definition I have (and that I got diagnosed with) a sex change does cure it, and it certainly did for me.

As to homework: National Geographic, July 2005, page 27, last paragraph. A boy receives a bone marrow stem cell treatment using cord blood. Since the stem cells came from a female he will produce blood with XX chromosomes for the rest of his life.

Now, do you go around testing the DNA of the people you meet so you know whether to address them as male or female? That must be expensive and time-consuming. And what do you do when you meet someone with three sex chromosomes? The English language has no pronouns for such people... and by the way have you ever asked yourself why that is?