(CNN) -- Henry Joseph Madden was a good student and track team member in high school, but he had a secret: He sometimes wore his mother's pantyhose and underwear under his clothes.



Dr. Jennifer Madden, a family physician, began her transition to being female at age 48.



"I really wanted to be a girl so bad, and that was one way for me to satisfy those feelings," Madden said. "I always felt like someone was looking over my shoulder."



The desire to be female never went away. At age 48, Madden confessed these feelings to a doctor, and started seeing a gender therapist who suggested Madden was transgendered.



Through reconstructive surgeries, electrolysis, laser procedures and voice lessons, Henry Joseph became Jennifer Elizabeth, known as Jenny. She is a practicing family physician in Nashua, New Hampshire.  Watch Jenny's story »



Chastity Bono, child of performer Cher and the late entertainer and politician Sonny Bono, announced Thursday the beginning of a transition from female to a male.



While still relatively rare -- one advocate estimates that 0.25 to 0.5 percent of the American population is transgendered -- the idea of changing gender identity has become more widespread in recent years. The term "LGBT" (Lesbian, Gay, Bisexual, Transgender) is more commonly recognized, and transgendered people have been portrayed in the 1999 film "Boys Don't Cry" as well as the 2002 book "Middlesex" by Jeffrey Eugenides.



Many people who have transitioned, including Madden, say they knew they had been born into the wrong gender from childhood. As early as age 3, Dr. Julie Praus, born male, didn't understand why her father wanted to play catch. As a boy, Praus learned how to fish and hunt, but enjoyed collecting Depression-era glassware vases. Praus, 48, a psychiatrist in Brattleboro, Vermont, started living as a woman in March 2008.



"I get up every morning and say, 'Wow, I can actually look at myself in the mirror,' because I've never been able to do that in my life, because what would stare back at me was not me," Praus said. iReport.com: Share your story of gender change



Doctors speculate that there is a biological foundation to gender identity, but no one has determined what in the biological makeup determines that gender. The interactions between personality and culture also contribute to identity, said Chris Kraft, clinical director at the Johns Hopkins Sexual Behaviors Consultation Unit.



The process of changing genders



For people who want a gender change on a biological level, the first step is therapy, experts say. Dr. Gary Alter, a plastic surgeon in Beverly Hills, California, said patients don't come to him until they've been in therapy, a process that can take as much as a year.



A therapist then gives a physician approval to start the patient on hormone treatment. At that point, the patient may or may not start living as the chosen sex, Alter said.



Females seeking to transition into males may elect to have their breasts removed via surgery. With testosterone, they will grow hair on their face and chest after about two years. Read one man's female-to-male advice to Chaz Bono



A higher percentage of males transitioning to females will go forward with genital surgery than females going to males, Alter said. Surgical methods for creating a penis -- which range from making one out of the clitoris to using the skin from the forearms -- are "not perfect," and many patients are happy with just chest surgery, he said.



Genital surgeries for creating female genitalia are better, he said. Alter's method is to make a clitoris out of the head of the penis, and make space for a vagina.



Facing the rest of the world



It is rare for people to undergo a gender transition and then want to reverse it, especially when surgery is involved, experts say.



Some say changing genders is one of the best things they've done, like Jamison Green, 60, author of "Becoming a
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