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Cytochrome P450, family 21, subfamily A, polypeptide 2
Symbol(s) CYP21A2; CPS1; CA21H; CAH1; CYP21; CYP21B; MGC150536; MGC150537; P450c21B
External IDs OMIM: 201910 MGI: 88591 Homologene: 68063
RNA expression pattern

More reference expression data

Human Mouse
Entrez 1589 13079
Ensembl ENSG00000168482 ENSMUSG00000024365
Uniprot P08686 A0JP50
Refseq NM_000500 (mRNA)
NP_000491 (protein)
NM_009995 (mRNA)
NP_034125 (protein)
Location Chr c6_COX: 32.1 - 32.1 Mb Chr 17: 34.41 - 34.41 Mb
Pubmed search [1] [2]

Steroid 21-hydroxylase (or steroid 21-monooxygenase or 21α-Hydroxylase; EC is a cytochrome P450 enzyme which is involved with the biosynthesis of the steroid hormones aldosterone and cortisol.

The CAS number is 9029-68-9.

21-Hydroxylase is encoded by the gene CYP21B.



It catalyses the hydroxylation of the carbon atom 21 in steroids (adding an "–OH"), which is necessary with the formation of these hormones.



Clinical significance

A defect within the CYP21B gene causes a disturbance of the development of the enzyme, which leads to congenital adrenal hyperplasia due to 21-hydroxylase deficiency. A related pseudogene is located near this gene; gene conversion events involving the functional gene and the pseudogene are thought account for many cases of steroid 21-hydroxylase deficiency.[1]


  1. ^ Entrez Gene: CYP21A2 cytochrome P450, family 21, subfamily A, polypeptide 2.

Further reading

  • White PC, Tusie-Luna MT, New MI, Speiser PW (1994). "Mutations in steroid 21-hydroxylase (CYP21).". Hum. Mutat. 3 (4): 373-8. doi:10.1002/humu.1380030408. PMID 8081391.
  • Helmberg A (1993). "Twin genes and endocrine disease: CYP21 and CYP11B genes.". Acta Endocrinol. 129 (2): 97-108. PMID 8372604.
  • de-Araujo M, Sanches MR, Suzuki LA, et al. (1996). "Molecular analysis of CYP21 and C4 genes in Brazilian families with the classical form of steroid 21-hydroxylase deficiency.". Braz. J. Med. Biol. Res. 29 (1): 1-13. PMID 8731325.
  • Yu CY (1999). "Molecular genetics of the human MHC complement gene cluster.". Exp. Clin. Immunogenet. 15 (4): 213-30. PMID 10072631.
  • Forest MG, Tardy V, Nicolino M, et al. (2005). "21-Hydroxylase deficiency: an exemplary model of the contribution of molecular biology in the understanding and management of the disease.". Ann. Endocrinol. (Paris) 66 (3): 225-32. PMID 15988383.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "21-Hydroxylase". A list of authors is available in Wikipedia.
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