Sikhandi was born a girl, but raised as a boy 5000 years when Krishna was on the planet. She even married a girl, but when the girl found her husband was actually a woman, reported to her father who then became enraged.
But Sikhandi's father, Maharaja Drupada said Sikhandi, his daughter was indeed a man. Somehow by the twist of fate, Sikhandi was once walking in the forest and met a yaksa, who agreed to swap his sex for a temporary period with Sikhandi, as Sikhandi had some purpose to fulfil.
The sex swapping was done and Sikhandi became a man. Thats was the reason during the Mahabharata battle, Bhismadeva would not face Sikhandi to fight, as it was against his principle to fight a woman as he new Sikhandi was born a woman, who had changed his sex to become a man.
So transgending is nothing new. It has been since the Vedic time and has also being in every culture. I vividly remembered as a child growing up in Africa, I knew of a woman who would actually lived as a man, would only wears man's dress and would only cut her hair like a man.
So its mightily strange phenomena that a person could indeed feel being in the wrong body. Being in the wrong body is also result of karma or should I say, twisted karma.