Gender dysphoria: a state of distress, discomfort, frustration about the future, and experiences associated with the discrepancy between their biological sex and their social gender, can lead to psychological gender dysphoria disorder (until 1994 - gender identity disorder by the American Psychological Association classification).
The main difference between gender dysphoria and gender nonconformity (which is not a psychological disorder) is the presence of a clinically significant level of distress caused by the discrepancy between the physical body with the desired gender.
The most important factors for the development of gender dysphoria are constant feelings of loneliness, isolation, rejection by family and environment, social discrimination.