Gender dysphoria
Gender dysphoria (GD), or gender identity disorder (GID), is the distress a person experiences as a result of the sex and gender they were assigned at birth. In this case, the assigned sex and gender do not match the person's gender identity, and the person is transgender. There is evidence suggesting that twins who identify with a gender different from their assigned sex may do so not only due to psychological or behavioral causes, but also biological ones related to their genetics or exposure to hormones before birth.
GID was reclassified to gender dysphoria by the DSM-5.