Genetic disorder in an isolated Caribbean village causes little girls to turn into boys and grow penises when they hit puberty

About 1 in 90 girls in an isolated Caribbean village become male and grow penises when they hit puberty due to a rare genetic disorder.
Children born in Salinas in Dominican Republic make the transition by the time they reach 12. The condition is so common there that it is no longer considered abnormal. The children who transition are simply referred to as the "guevedoces" – which literally translates as "penis at 12"
BBC2 series, Countdown to Life - the Extraordinary Making of You, explored the lives of these children known as pseudohermaphrodite. One of such kids featured in the documentary is Johnny. Johnny appeared female at birth and was named Felicitia. He had no penis and as such was raised as a girl. However, when he clocked 7 he began to transform into a male with his penis eventually growing out. Now 24, Johnny is physically and biologically male.

He said: "I remember I used to wear a little red dress. I was born at home instead of in a hospital. They didn't know what sex I was. I went to school and I used to wear my skirt. I never liked to dress as a girl.  When they bought me girls toys I never bothered playing with them. All I wanted to do was play with the boys."

The rare genetic disorder is caused by a missing enzyme which prevents the production of a type of male sex hormone - dihydro-testosterone - in the womb. All babies in the womb, whether male or female, have internal glands known as gonads and a small bump between their legs called a tubercle. At around eight weeks old, male babies who carry the Y chromosome start to produce dihydro-testosterone in large amounts - this turns the tubercle into a penis. For females, it becomes a clitoris.

But some male babies are missing the enzyme 5-α-reductase which triggers the hormone surge. This means they appear to be born female with no testes and what looks very much like a vagina. Then when puberty hits, a large surge of testosterone is triggers the male reproductive organs to grow. This causes their voices to deepen and the development of a penis. Essentially, the development that should have taken place in the womb with these children happens around 12 years later.