The research, led by the National Institute of Psychiatry, interviewed 250 transgender people and found that it is not a mental disorder as once believed. Apparently, distress and impairment are the two essential characteristics of a mental disorder, and they found transgender people can experience some distress but not because they are transgender, but because of social rejection and violence.
New Study Finds That Transgender Identity Is Not A Mental Disorder
The Brain Squirrel Monologues 