There has been a lot of research into what causes someone to be transgender. As the Crossport Gender Support Group explains,
Theories of both psychological and biological causality have been forwarded and it is quite likely there are different causes for different individuals. Lately, strong research suggests that an incorrect amount of miss-timed secretion of male hormone during stages of fetal development may create a transgendered individual - whether male or female. Biologically, nature will produce a female unless male androgens are supplied at the right times and in the right amounts. There are physiological and mental gray areas between male and female "absolutes". Additionally, there are some theories arguing a genetic model of causality.
The Gender Identity Disorder Label
Despite the fact that the causes of a transgender identity aren't known, being transgender has typically been viewed as a psychological issue. In fact, it even has its own psychiatric diagnosis in the Diagnostic and Statistical Manual of Mental Disorders: "Gender Identity Disorder." Of course not everyone feels that such a label is appropriate.
A Medical Not Psychological Issue
Dr. Norman P. Spack, the co-founder of the Gender Management Services Program, a clinic that provides treatments to delay puberty in children questioning their gender, feels that we should look at a transgender identity as a medical condition, not as a psychiatric disorder.
As he explained during a Harvard Transgender Awareness Week event, "These people aren't crazy. It's a medical condition."
The Impact on Transgender Teens
If this view becomes widespread, it could really affect the way trans teens are treated. Currently, most are not allowed surgery or hormone treatment because of their age.
As a teen transman writes on the forum,
"My parents haven't let me take testosterone yet, and probably won't for at least a year, so that's out of the question for a while (which sucks, because I currently pass as a pretty young boy, imho, and will very soon need testosterone to look my age)."
And while it is controversial, allowing teens to begin transitioning can be very beneficial. In fact, studies have found that adolescents who started hormone therapy as teens, had fewer psychological problems than people who started transitioning in adulthood.
So while we might not know what causes someone to be transgender, we are learning more and more about how we can help make the transition easier.