Guevedoces: individuals reported to apparently change gender naturally at puberty, from female to male. These people have been observed in an isolated village in the Dominican Republic and in the eastern highlands of Papua New Guinea. Infants with female appearance at birth begin to develop physical characteristics of a male during puberty. These individuals have been referred to by different names in their own regions, including guevedoces, translated to mean "penis at age twelve," and machihembras, which means "first a woman, then a man." In Papua New Guinea, the locals called these individuals turnims, meaning "expected to become men."
Affected individuals are born with male (XY) chromosomes. Because of a deficiency of the 5 a-reductase enzyme, testosterone is not converted to the biologically active form, dihydrotestosterone (DHT). In the absence of DHT, the infant's external genitalia appear to be an ambiguous clitoris and labia. Studies have shown this condition to be inherited in an autosomal recessive manner, meaning that to be affected, an individual must receive a copy of the genetic defect from each parent.
REFERENCE: Issues Berkeley Medical Journal at UC Berkeley. "The Guevedoces: Gender metamorphosis at work." 2005.