Ordinarily when a fetus is genetically male (has 46,XY chromosomes), this is how development happens: Early in fetal development, the proto-gonads (cells that will become gonads) become testes. The testes start putting out testosterone. The fetus’s body makes a chemical enzyme called 5-alpha reductase (5-AR), and the 5-AR converts some of the testosterone into dihydrotestosterone. The dihydrotestosterone contributes to the fetus’s genitals developing as the male type.
When the typical boy reaches puberty, the testes make a lot more testosterone. The enzyme 5-AR isn’t needed at this point for the testosterone to have an affect on the body. So the boy’s body matures along the male pathway. The boy’s penis grows, his voice drops, he develops male-typical face and body hair and male-typical musculature.
If a fetus has 5-AR deficiency (5-ARD), that means that the fetus’s body lacks the enzyme 5-AR. So, early in development, the proto-gonads become testes and they start to make testosterone. But because the enzyme 5-AR is missing, the testosterone doesn’t become dihydrotestosterone. As a result, the fetus’s genitals form more like the typical female’s. When the child is born, the genitals may look ambiguous or fairly female-typical. (In some cases, children with 5-ARD have been assumed to be females and have been raised female.)
At puberty, the child’s testes will make lots more testosterone. Remember now the enzyme 5-AR isn’t necessary for the testosterone to have an affect on sexual maturation at this point. So the child (regardless of which gender the child was raised as) will undergo a male-typical puberty. The phallus will grow to look bigger, more like a penis, the voice will drop as it does in a typical male, the child will develop male-typical face and body hair and male-typical musculature.
Posted in: Specific Conditions