In humans, the enzyme is localized in endoplasmic reticulum membranes of cells in adrenal cortex,[14][15] and is encoded by the CYP21A2gene which is located near the CYP21A1Ppseudogene that has high degree of sequence similarity. This similarity makes it difficult to analyze the gene at the molecular level, and sometimes leads to loss-of-function mutations of the gene due to intergenic exchange of DNA.
^"UniProt". www.uniprot.org. Archived from the original on 28 November 2023. Retrieved 26 November 2023.
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^Sarafoglou K, Lorentz CP, Otten N, Oetting WS, Grebe SK (July 2012). "Molecular testing in congenital adrenal hyperplasia due to 21α-hydroxylase deficiency in the era of newborn screening". Clinical Genetics. 82 (1): 64–70. doi:10.1111/j.1399-0004.2011.01694.x. PMID21534945. S2CID7197547.
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^ This article incorporates public domain material from "NCBI: CYP21A2 cytochrome P450 family 21 subfamily A member 2". Reference Sequence collection. National Center for Biotechnology Information. Retrieved 30 November 2020. This gene encodes a member of the cytochrome P450 superfamily of enzymes. The cytochrome P450 proteins are monooxygenases that catalyze many reactions involved in drug metabolism and synthesis of cholesterol, steroids, and other lipids. This protein localizes to the endoplasmic reticulum and hydroxylates steroids at the 21 position. Its activity is required for the synthesis of steroid hormones including cortisol and aldosterone. Mutations in this gene cause congenital adrenal hyperplasia. A related pseudogene is located near this gene; gene conversion events involving the functional gene and the pseudogene are thought to account for many cases of steroid 21-hydroxylase deficiency. Two transcript variants encoding different isoforms have been found for this gene.
^Neunzig J, Milhim M, Schiffer L, Khatri Y, Zapp J, Sánchez-Guijo A, et al. (March 2017). "The steroid metabolite 16(β)-OH-androstenedione generated by CYP21A2 serves as a substrate for CYP19A1". The Journal of Steroid Biochemistry and Molecular Biology. 167: 182–191. doi:10.1016/j.jsbmb.2017.01.002. PMID28065637. S2CID36860068.