In an isolated village in the Dominican Republic, an estimated one in fifty children are born appearing to be girls but grow male genitalia during puberty.
The children are known as Guevedoces, roughly translating as “penis-at-12”, referring too the age where their appearance often starts to change.
A BBC documentary called Countdown to Life: The Extraordinary Making of You explores the rare condition as part of a series on development.
Johnny, once known as Felicita, told the programme he fought bullies who targeted him when the change started.
"They used to say I was a devil, nasty things, bad words and I had no choice but to fight them because they were crossing the line,” he said.
"I'd like to get married and have children, a partner who will stand by me through good and bad.”
The documentary also features seven-year-old Carla, who will soon become known as Carlos.
The child’s mother said she could see the transformation starting from the age of five, adding: “I love her however she is. Girl or boy, it makes no difference."
Dr Julianne Imperato- McGinley, an endocrinologist at Cornell University in the US, investigated the phenomenon in the early 1970s.
According to the Urological Sciences Research Foundation the Guevedoces were also known locally as “Machihembras” - first women, then man.
She found that pseudohermaphrodites appeared to be girls at birth but developed muscles, testes and a penis during puberty as a result of an enzyme deficiency with 5-alpha Reductase.
It is needed to convert testosterone to the biologically active dihydrotestosterone (DHT). Without it, the external genitalia appear similar to a female clitoris and labia.
In a 2005 article published in the Berkley Medical Journal Elizabeth Kelley wrote that in the years following Dr Imperato-McGinley’s original research, reports suggested that this was also common in the Sambian villages of Papua New Guinea, where the locals called the children “turnims”, meaning “expected to become men”.
“The Sambians view these children as flawed males; the children are rejected and humiliated by their families and society,” Kelley wrote.
“On the other hand, in the Dominican Republic, the birth of a pseudohermaphrodite is fully accepted and during puberty, the child’s physical transformation into a male is marked by joyous celebration.”
The observation that Guevedoces tended to have small prostates led to the development of a drug that has helped millions of men, the BBC reported.
Roy Vagelos, head of research at Merc pharmaceuticals, created Finasteride, which blocks the action of 5-alpha-reductase and is used to treat the benign enlargement of the prostate and male pattern baldness.
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