For musician Eden Atwood, there have been few signs of the dark secret concealed within her body. A secret so seemingly monstrous, Eden wasn't supposed to know.
"If my mother didn't think I should know, and my father didn't think I should know, and the doctors didn't think I should know," Atwood said, "I shouldn't let anybody else know."
What could possibly be so wrong? Throughout her life, Atwood appeared to be the picture of health. She blossomed from an adorable young girl into a striking beauty. She even became a model, an actress and an accomplished jazz singer.
As a teenager, Atwood began to sense that something was wrong.
"I was the last one not to have had her period," she admitted, "and I didn't like it one bit. And my mother was saying, you know, 'don't worry about it.' But I was worried. I was really worried."
After several tests, doctors gave her bad news. They told Atwood her ovaries were twisted and cancer-prone, and that they'd have to be removed. Worse yet, the surgery would leave her infertile. She was understandably devastated.
But there was more troubling news to come. When Atwood was just 15, her stepmother blurted out something she was never supposed to, something almost unbelievable.
"She told me, 'you know, they lied to you,'" Atwood told ABC News' Juju Chang. "'You're really half-man, half-woman.'"
Surprisingly, the cutting comment didn't sound entirely crazy to Atwood.
"It made sense," she said, "Something's weird. No one's telling the truth. I can tell something's not right. This fits. I'm a freak."
Atwood is not a freak -- nor is she half-man, half-woman. But her DNA says she's a man. That's because she has male chromosomes, an X and a Y, instead of two Xs, like most females. It's a disorder of sexual development in the womb called Androgen Insensitivity Syndrome, or AIS. It can be passed down through the mother or occur as a spontaneous mutation.
"There are probably about seven-and-a-half thousand people, women, in the U.S. with the condition," said Dr. Charmian Quigley, a pediatric endocrinologist.
Despite the male chromosomes, Quigley said, women with AIS are just that -- women.
"They have a vagina, like anybody else's," she said, "but it's basically just a pouch, it's not connected to a uterus. There is no uterus. But what they have internally is testes that you would typically find in a male."
It turns out the doctors had lied to Atwood about having twisted ovaries. She really had internal testicles.
All of us, men and women, have a mix of male and female hormones running through our systems. And as you might expect, the testes of women with AIS produce huge amounts of the typically male hormone testosterone. But here's the hitch: their bodies can't process any of it. And amazingly, they turn it into the typically female hormone estrogen, giving them much more estrogen than the average woman.
These women don't get acne, and have no body odor and minimal sweating. In essence, they are the furthest thing from a male that there could be.
So, why keep it a secret from them? Quigley explained that there was a concept that "if you told them that they had a Y chromosome, or a testicle inside them, but they were externally female, they would completely meltdown."
She even showed ABC News a 1970s medical textbook that says, "It is of no benefit to disclose that the gonads were testes instead of ovaries."