Androgen biosynthesis in the human fetus proceeds through the adrenal sex
steroid precursor
dehydroepiandrosterone, which is converted to
testosterone in the gonads, followed by further activation to 5α-dihydrotestosterone in genital skin, thereby facilitating male external genital differentiation.
Congenital adrenal hyperplasia due to P450
oxidoreductase deficiency results in disrupted
dehydroepiandrosterone biosynthesis, explaining undervirilization in affected boys. However, many affected girls are born virilized, despite low circulating
androgens. We hypothesized that this is due to a prenatally active, alternative
androgen biosynthesis pathway from 17α-hydroxyprogesterone to 5α-dihydrotestosterone, which bypasses
dehydroepiandrosterone and
testosterone, with increased activity in
congenital adrenal hyperplasia variants associated with 17α-hydroxyprogesterone accumulation. Here we employ explant cultures of human fetal organs (adrenals, gonads, genital skin) from the major period of sexual differentiation and show that alternative pathway
androgen biosynthesis is active in the fetus, as assessed by liquid chromatography-tandem mass spectrometry. We found
androgen receptor expression in male and female genital skin using immunohistochemistry and demonstrated that both 5α-dihydrotestosterone and adrenal explant culture supernatant induce nuclear translocation of the
androgen receptor in female genital skin primary cultures. Analyzing urinary
steroid excretion by gas chromatography-mass spectrometry, we show that neonates with P450
oxidoreductase deficiency produce
androgens through the alternative
androgen pathway during the first weeks of life. We provide quantitative in vitro evidence that the corresponding P450
oxidoreductase mutations predominantly support alternative pathway
androgen biosynthesis. These results indicate a key role of alternative pathway
androgen biosynthesis in the prenatal
virilization of girls affected by
congenital adrenal hyperplasia due to P450
oxidoreductase deficiency.