Bradley Manning's statement that he'll no longer be a "he" but rather a "she" named Chelsea Manning sets the Army private on a path that most transgender individuals have taken.

But for many unfamiliar with the "trans" community, such an announcement raises a host of questions. Just getting a count is difficult, but a 2011 report from the Williams Institute, a think tank on sexual orientation and gender identity, suggests nearly 700,000 transgender individuals live in the USA.

An online fact sheet from the American Psychological Association defines "transgender" as an "umbrella term for persons whose gender identity, gender expression, or behavior does not conform to that typically associated with the sex to which they were assigned at birth."

But even mental health professionals who specialize in gender identity say there is much about being transgender that is unclear, so classifying it for treatment purposes is challenging.

"It's different from other mental disorders," says Jack Drescher, a New York psychiatrist who was part of the American Psychiatric Association's work group on gender identity, which revised the latest manual of mental disorders, the DSM-5.

"Usually with a mental disorder, we try and change the person's mind," he says. "This is the only mental disorder where the treatment is changing the body. In a typical mental disorder, we try to make those symptoms go away. Here the treatment has emerged to align the person's body to match their gender identity."

STORY: Medical issues for transgendered people go beyond surgery

For people who feel they're really a different gender than the one they were born, the new manual changed the diagnostic name from "gender identity disorder" to "gender dysphoria," which refers to the distress that may be associated with it.

Drescher says the challenge was to reduce stigma and yet maintain access to medical care, which can include psychological support as well as hormones or surgical treatment. All the treatments require a diagnosis for insurance, he says.

"It's not called a disorder, but it is in the handbook of mental disorders," Drescher says. "The truth is we actually don't know what it is. Is it a mental disorder or does the cause of gender dysphoria lie somewhere else? We don't know what causes it, so there's no absolute reason why it has to be in the mental disorders section, except as a fact of history, it's always been there."

The DSM is the Diagnostic and Statistical Manual of Mental Disorders, but until the manual's second revision in 1973, homosexuality had been included as a mental disorder. Now Drescher is working on a committee of the World Health Organization, which is revising another standard diagnostic tool, the International Classification of Diseases (ICD). The revision is altering both the name and classification, he says.

What had been called "transsexualism" is now recommended to be "gender incongruence" in the ICD-11, slated for 2015. Drescher says the proposal is to move the gender diagnosis out of the mental disorder section and put it in another, yet undecided, section.

"It couldn't been done in the DSM since it's only a manual of mental disorders and we had no place else to put it," Drescher says.

Nicole Joseph, a clinical psychologist in Fairfax, Va., who specializes in treating transgender individuals, says most of her clients have felt "disconnected" from their body since early childhood.

Psychological treatment is overall support for any depression or distress and support for the identified gender rather than the physically assigned gender, she says.

"There are institutions that will advocate for people staying their assigned gender, but many studies find it's more harmful for the individual," she says. "What most reputable therapists do is support the individual and talk about the gender dysphoria and make sure it's not just temporary."

She says most endocrinologists who might prescribe hormone therapy would want a patient in psychological therapy a minimum of three to six months and up to a year before intervening. She says most of her clients do pursue the hormone option over surgery.

"The process of coming out as transgender is very different than coming out as gay," Joseph says. "Many of my transgender patients express that coming out as 'trans' now is what coming out as gay was in the 1980s."

"Coming out as trans is a very different emotional process for families," she adds. "Going from having a daughter to having a son is a huge emotional process. Name changes and pronoun changes are also very difficult for family members to accept."