Rare Condition Causes Some Dominican Republic Girls to Become Boys at Puberty

During the first week after conception a fetus hasn’t yet developed its gender. In small communities in the Dominican Republic, this sometimes won't happen until a child reaches puberty when some girls quite literally transform into boys. REUTERS/Alessandro Bianchi

Puberty is a universally confusing experience. The hormonal, physical and emotional changes a child undergoes in that time can be overwhelming. But imagine puberty came with a sudden gender transformation. It's a concept that seems as if it were right out of science fiction but for a small community in the Dominican Republic it's common for girls to hit puberty and quite literally transform into boys.

The new BBC Two series "Countdown to Life" looks at the fascinating phenomenon of children in this community who are born girls and then spontaneously develop penises once they've entered puberty. They are called guevedoces, which loosely translates to "penis at twelve." They are also sometimes referred to as machihembras, which means "first a woman, then a man."

During interviews in the documentary, several of the children report not feeling like a girl, even before hitting puberty and growing a penis. Johnny, formerly Felicita, told the filmmakers that when he was young he'd go to school in a little red dress but was never happy participating in activities that interested girls.

"I never liked to dress as a girl, and when they bought me toys for girls I never bothered playing with them—when I saw a group of boys I would stop to play ball with them," he told the filmmakers. Kids at school bullied Johnny once it became clear that he was a guevedoces.

According to the filmmakers, one in 90 boys in the communities in the Dominican Republic is a pseudo-hermaphrodite. Researchers at the University of California Berkeley say this condition has also been identified in children living in the eastern highlands of Papua New Guinea. Local physicians have become more attuned to identifying which girls may turn out to be guevedoces at the onset of puberty but that doesn't mean it's now less common.

When a baby is normally conceived it will either have two X chromosomes and become a girl or one X and one Y chromosome and develop into a boy. However, during the first week after conception the fetus hasn't yet developed its gender. The sex hormones are triggered eight weeks into the pregnancy. A fetus with a Y chromosome will have critical developmental changes at this point: The gonads become testicles, which triggers the release of testosterone to a nodule called the tubercle. This process stimulates a more powerful hormone called dihydrotestosterone that makes the tubercle become a penis. Female fetuses don't produce dihydrotestosterone and the tubercle becomes a clitoris.

But with guevedoces, the testosterone never transforms into dihydrotestosterone while in the womb. Dr. Julianne Imperato-McGinley, a professor of medicine and endocrinology with Cornell Medical College in New York, visited the communities and uncovered the mystery behind this genetic disorder. She found these kids had low levels of 5-alpha-reductase, an enzyme that helps to convert testosterone into dihydrotestosterone. This delays the development of male genitalia.

The BBC article explains: "At puberty, like other boys, they get a second surge of testosterone. This time the body does respond and they sprout muscles, testes and a penis."

Once fully grown, the male genitalia of the guevedoces are smaller than average, but a girl-turned-boy will achieve complete sexual and reproductive function. Guevedoces eventually develop more masculine facial features, though they have a have a minimal amount of facial hair. They also have a smaller-than-average size prostate.

This last attribute was of greatest interest to Roy Vagelos, who in the 1970s led the research team at Merck, the pharmaceutical company. He took an interest in how the hormonal changes may have something to do with the prostate size. The research eventually led to the development of the drug finasterine, which blocks the action of 5-alpha reductase, emulating the absence of dihydrotestosterone that occurs in guevedoces. The drug is used today to treat enlarged prostate and male pattern baldness.