5-alpha reductase deficiency is a condition that affects sexual development before birth and during puberty. People with this condition are genetically male, with one X and one Y chromosome in each cell, and they have male gonads (testes). Their bodies, however, do not produce enough of a hormone called dihydrotestosterone (DHT). DHT has a critical role in male sexual development, and a shortage of this hormone disrupts the formation of the external sex organs before birth.

Many people with 5-alpha reductase deficiency have external genitalia that appears female. In other cases, affected infants have male-typical external genitalia, often an unusually small penis (micropenis) and the urethra opening on the underside of the penis (hypospadias). Still other affected infants have external genitalia do not look clearly male or clearly female.

During puberty, an increase in the levels of male sex hormones leads to the development of some secondary sex characteristics, such as increased muscle mass, deepening of the voice, development of pubic hair, and a growth spurt. The penis and scrotum (the sac of skin that holds the testes) may grow larger. People with 5-alpha reductase deficiency do not develop much facial or body hair. Most affected individuals are unable to have biological children (infertile) without assisted reproduction.

5-alpha reductase deficiency is a rare condition; the exact incidence is unknown. Large families with affected members have been found in several countries, including the Dominican Republic, Papua New Guinea, Turkey, and Egypt.

Variants (also called mutations) in the SRD5A2 gene cause 5-alpha reductase deficiency. The SRD5A2 gene provides instructions for making an enzyme called steroid 5-alpha reductase 2. This enzyme is involved in processing androgens, which are hormones that direct male sexual development. Specifically, the steroid 5-alpha reductase 2 enzyme is responsible for a chemical reaction that converts the hormone testosterone to DHT. DHT is essential for the normal development of male sex characteristics before birth, particularly the formation of the external genitalia.

Variants in the SRD5A2 gene prevent steroid 5-alpha reductase 2 from effectively converting testosterone to DHT in the developing reproductive tissues. These hormonal factors underlie the changes in sexual development seen in infants with 5-alpha reductase deficiency.

During puberty, the testes produce more testosterone.  Researchers believe that people with 5-alpha reductase deficiency develop secondary male sex characteristics in response to higher levels of this hormone.  Some affected people also retain a small amount of 5-alpha reductase 2 activity, which may produce DHT and contribute to the development of secondary sex characteristics during puberty.

Genetic Testing Information

• Genetic Testing Registry: 3-Oxo-5 alpha-steroid delta 4-dehydrogenase deficiency

Genetic and Rare Diseases Information Center

• 46,XY disorder of sex development due to 5-alpha-reductase 2 deficiency

Patient Support and Advocacy Resources

• National Organization for Rare Disorders (NORD)

Clinical Trials

• ClinicalTrials.gov

Catalog of Genes and Diseases from OMIM

• PSEUDOVAGINAL PERINEOSCROTAL HYPOSPADIAS; PPSH

Scientific Articles on PubMed

• PubMed

• Bahceci M, Ersay AR, Tuzcu A, Hiort O, Richter-Unruh A, Gokalp D. A novel missense mutation of 5-alpha reductase type 2 gene (SRD5A2) leads to severe male pseudohermaphroditism in a Turkish family. Urology. 2005 Aug;66(2):407-10. doi: 10.1016/j.urology.2005.02.021. Citation on PubMed
• Baldinotti F, Majore S, Fogli A, Marrocco G, Ghirri P, Vuerich M, Tumini S, Boscherini B, Vetri M, Scommegna S, Rinaldi R, Simi P, Grammatico P. Molecular characterization of 6 unrelated Italian patients with 5alpha-reductase type 2 deficiency. J Androl. 2008 Jan-Feb;29(1):20-8. doi: 10.2164/jandrol.107.002592. Epub 2007 Jul 3. Citation on PubMed
• Cohen-Kettenis PT. Gender change in 46,XY persons with 5alpha-reductase-2 deficiency and 17beta-hydroxysteroid dehydrogenase-3 deficiency. Arch Sex Behav. 2005 Aug;34(4):399-410. doi: 10.1007/s10508-005-4339-4. Citation on PubMed
• Hackel C, Oliveira LE, Ferraz LF, Tonini MM, Silva DN, Toralles MB, Stuchi-Perez EG, Guerra-Junior G. New mutations, hotspots, and founder effects in Brazilian patients with steroid 5alpha-reductase deficiency type 2. J Mol Med (Berl). 2005 Jul;83(7):569-76. doi: 10.1007/s00109-005-0651-7. Epub 2005 Mar 16. Citation on PubMed
• Lee PA, Houk CP, Ahmed SF, Hughes IA; International Consensus Conference on Intersex organized by the Lawson Wilkins Pediatric Endocrine Society and the European Society for Paediatric Endocrinology. Consensus statement on management of intersex disorders. International Consensus Conference on Intersex. Pediatrics. 2006 Aug;118(2):e488-500. doi: 10.1542/peds.2006-0738. No abstract available. Citation on PubMed
• Okeigwe I, Kuohung W. 5-Alpha reductase deficiency: a 40-year retrospective review. Curr Opin Endocrinol Diabetes Obes. 2014 Dec;21(6):483-7. doi: 10.1097/MED.0000000000000116. Citation on PubMed
• Sultan C, Lumbroso S, Paris F, Jeandel C, Terouanne B, Belon C, Audran F, Poujol N, Georget V, Gobinet J, Jalaguier S, Auzou G, Nicolas JC. Disorders of androgen action. Semin Reprod Med. 2002 Aug;20(3):217-28. doi: 10.1055/s-2002-35386. Citation on PubMed