ESPE Yearbook of Paediatric Endocrinology

To read the full abstract: Proc Natl Acad Sci U S A. 2019; 116(44): 22294-22299. PMID: 31611378.

Androgen biosynthesis in the human fetus proceeds through the adrenal sex steroid precursor dehydroepiandrosterone (DHEA), which is converted to testosterone in the gonads, followed by further activation to 5α-dihydrotestosterone (DHT) in genital skin, thereby facilitating male external genital differentiation (1). Congenital adrenal hyperplasia (CAH) due to P450 oxidoreductase deficiency (PORD) is an inborn disorder that results in disrupted DHEA biosynthesis, leading to undervirilization of affected boys. However, some affected girls present with severe genital virilization at birth, despite low circulating androgen concentrations (2-4). Here, Reisch et al. hypothesized that this might be explained by a prenatally active, alternative biosynthesis pathway to 5α-DHT. They investigated the presence of an alternative androgen-producing pathway in human fetuses.

Human fetal organ explant cultures of adrenal, gonad, and genital skin tissue collected at 6 to 10 weeks post conception from 30 fetuses were incubated with steroid precursors, and conversion products were measured using LC–MS/MS. In addition, urinary steroid profiles from three neonates with PORD were analysed and compared with profiles of 9 healthy controls during the first 90 days after birth. They found that explant incubations with female tissues convert some 17OHP to androstenedione via the classical pathway in the adrenal, ovary and genital skin, but testosterone was produced in only 2 of 9 female genital skin incubations, and not at all in adrenals and gonads. By contrast, all female tissues converted 17OHP to DHT via the proposed alternative androgen producing pathway and its intermediates. In male tissues, 17OHP was converted along the classical pathway to testosterone and in genital skin to DHT. In male adrenals, testis and genital skin, 17OHP was stepwise converted also via the alternative pathway to DHT. Confirmation with expression of the necessary steroidogenic enzymes was consistent with the above data. In addition, the authors found androgen receptor (AR) expression in male and female genital skin using immunohistochemistry, and demonstrated that both 5α-DHT and adrenal explant culture supernatant induce nuclear translocation of the androgen receptor in female genital skin primary cultures. In 3 neonates with a 46, XY karyotype and a PORD mutation known to cause normal male external genitalia, but female virilization in case of a girl, the authors identified urinary metabolites consistent with the adrenal gland being the major site of the alternative androgen producing pathway.

In conclusion, these data provide in vitro, ex vivo, and in vivo evidence for the existence and activity of an alternative pathway for the synthesis of the most potent androgen, DHT, during early human development. They demonstrate that, through co-operation of an adrenogenital steroidogenic unit, the alternative androgen pathway yields active androgen synthesis in the female fetus, with excess activity driving female virilisation in CAH due to PORD. Given that the alternative pathway substrate 17OHP also accumulates in 21-hydroxylase deficiency, it is conceivable that alternative pathway androgens contribute to prenatal virilization in this common form of CAH.

References:

1. MacLaughlin DT, Donahoe PK. Sex determination and differentiation. N Engl J Med. 2004; 350(4): 367-78.

2. Flück CE, Tajima T, Pandey AV, Arlt W, Okuhara K, Verge CF, Jabs EW, Mendonça BB, Fujieda K, Miller WL. Mutant P450 oxidoreductase causes disordered steroidogenesis with and without Antley-Bixler syndrome. Nat Genet. 2004; 36(3): 228–30.

3. Arlt W, Walker EA, Draper N, Ivison HE, Ride JP, Hammer F, Chalder SM, Borucka-Mankiewicz M, Hauffa BP, Malunowicz EM, Stewart PM, Shackleton CH. Congenital adrenal hyperplasia caused by mutant P450 oxidoreductase and human androgen synthesis: analytical study. Lancet. 2004; 363(9427): 2128–35.

4. Krone N, Reisch N, Idkowiak J, Dhir V, Ivison HE, Hughes BA, Rose IT, O’Neil DM, Vijzelaar R, Smith MJ, MacDonald F, Cole TR, Adolphs N, Barton JS, Blair EM, Braddock SR, Collins F, Cragun DL, Dattani MT, Day R, Dougan S, Feist M, Gottschalk ME, Gregory JW, Haim M, Harrison R, Olney AH, Hauffa BP, Hindmarsh PC, Hopkin RJ, Jira PE, Kempers M, Kerstens MN, Khalifa MM, Köhler B, Maiter D, Nielsen S, O’Riordan SM, Roth CL, Shane KP, Silink M, Stikkelbroeck NM, Sweeney E, Szarras-Czapnik M, Waterson JR, Williamson L, Hartmann MF, Taylor NF, Wudy SA, Malunowicz EM, Shackleton CH, Arlt W. Genotype-phenotype analysis in congenital adrenal hyperplasia due to P450 oxidoreductase deficiency. J Clin Endocrinol Metab. 2012; 97(2): E257–67.