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Gene

CYP21A2

cytochrome P450 family 21 subfamily A member 2

Summary

Cytogenetic location
6p21.33
Coordinates
Chromosome 6: 32,038,415–32,041,644 (GRCh38)
Exons
10 exons across 3.2 kb
Protein
495 amino acids
Inheritance
Autosomal recessive
Also known as
P450c21B, CA21H, CPS1, CAH1
Previous symbols
CYP21, CYP21B
MANE Select transcript
ENST00000644719.2NM_000500.9
Locus type
gene with protein product
  • Very high
  • Confident
  • Low
  • Very low

Reference genomeGRCh38

Positions on gene and variant pages follow this choice, in this browser.

Curated report relevant to this gene

  • Congenital Adrenal Hyperplasia

    • Autosomal recessive

      Congenital adrenal hyperplasia (CAH) is an inherited endocrine disorder caused by a steroidogenic enzyme deficiency that is characterized by adrenal insufficiency and variable degrees of hyper or hypo androgyny manifestations, depending of the type and the severity of the disease.

      • 3 GenCC submitters rate it definitive or strong
      What knowing changes

      Glucocorticoid replacement (hydrocortisone in children, prednisone/dexamethasone in adults); mineralocorticoid replacement for salt-wasting (fludrocortisone); adrenalectomy for severe medically refractory hyperandrogenism; stress dosing protocols

Inheritance

Autosomal recessive
It takes a changed copy from each parent. With one, you are a carrier and usually unaffected; when both parents are carriers, each child has a one-in-four chance of inheriting two.

How CYP21A2 is laid out

  • Coding sequence
  • Untranslated region
  • Intron
  • Direction of transcription
  • Known disease-causing sites
  • Stretches short reads find hard
Chromosome 6, with a bracket where CYP21A2 sits. CYP21A2 and 69 genes near it on chromosome 6, from 31,540,030 to 32,540,029.Chromosome 66p21.33p25.3p25.2p25.1p24.3p24.2p24.1p23p22.3p22.2p22.1p21.33p21.32p21.31p21.2p21.1p12.3p12.2p12.1p11.2p11.1q11.1q11.2q12q13q14.1q14.2q14.3q15q16.1q16.2q16.3q21q22.1q22.2q22.31q22.32q22.33q23.1q23.2q23.3q24.1q24.2q24.3q25.1q25.2q25.3q26q2731.6 Mb31.8 Mb32 Mb32.2 Mb32.4 MbDDX39B: 31,530,217–31,542,451, reverse strandATP6V1G2-DDX39B: 31,530,219–31,546,608, reverse strandATP6V1G2: 31,544,444–31,548,427, reverse strandNFKBIL1: 31,546,870–31,558,829, forward strandLTA: 31,572,054–31,574,324, forward strandLTATNF: 31,575,558–31,578,336, forward strandLTB: 31,580,525–31,582,522, reverse strandLST1: 31,581,065–31,588,911, forward strandLST1NCR3: 31,588,895–31,593,217, reverse strandNCR3AIF1: 31,615,214–31,617,025, forward strandAIF1PRRC2A: 31,620,675–31,637,771, forward strandPRRC2A: 31,622,774–31,622,860, forward strand: 31,623,874–31,625,499, forward strandBAG6: 31,638,543–31,652,747, reverse strandAPOM: 31,652,416–31,658,214, forward strandC6orf47: 31,658,298–31,660,778, reverse strandGPANK1: 31,661,228–31,666,283, reverse strandCSNK2B: 31,665,227–31,670,343, forward strand: 31,666,102–31,673,546, forward strandLY6G5B: 31,669,976–31,673,776, forward strandLY6G5C: 31,676,684–31,684,040, reverse strandLY6G5CABHD16A: 31,686,954–31,703,391, reverse strandABHD16ALY6G6F: 31,706,863–31,710,801, forward strandLY6G6F-LY6G6D: 31,706,904–31,717,918, forward strandLY6G6D: 31,715,285–31,717,919, forward strandMPIG6B: 31,718,594–31,726,714, forward strandLY6G6C: 31,718,648–31,721,746, reverse strandDDAH2: 31,726,586–31,730,617, reverse strandCLIC1: 31,730,579–31,740,558, reverse strandMSH5: 31,739,677–31,762,678, forward strandMSH5MSH5-SAPCD1: 31,740,020–31,764,851, forward strandSAPCD1: 31,762,656–31,764,851, forward strandVWA7: 31,765,590–31,777,328, reverse strandVWA7VARS1: 31,777,518–31,795,975, reverse strandLSM2: 31,797,019–31,806,992, reverse strandLSM2HSPA1L: 31,809,619–31,815,788, reverse strandHSPA1A: 31,815,543–31,817,994, forward strandHSPA1AHSPA1B: 31,827,738–31,830,254, forward strandHSPA1BNEU1: 31,857,063–31,862,905, reverse strandNEU1SLC44A4: 31,863,173–31,879,198, reverse strandSLC44A4EHMT2: 31,879,758–31,897,723, reverse strandEHMT2C2: 31,897,785–31,945,677, forward strandC2ZBTB12: 31,899,065–31,902,103, reverse strandZBTB12: 31,927,698–31,952,048, forward strandCFB: 31,945,650–31,952,086, forward strandCFBNELFE: 31,952,087–31,959,079, reverse strandSKIC2: 31,959,025–31,969,852, forward strandSKIC2DXO: 31,969,810–31,972,517, reverse strandDXOWHR1: 31,971,091–31,982,821, forward strandWHR1C4A: 31,981,991–32,005,247, forward strandC4AC4B: 32,014,725–32,035,975, forward strandC4BCYP21A2: 32,038,415–32,041,644, forward strandCYP21A2TNXB: 32,041,153–32,115,334, reverse strandTNXBATF6B: 32,115,264–32,128,255, reverse strandATF6BFKBPL: 32,128,697–32,131,070, reverse strandFKBPLPPT2: 32,146,580–32,163,679, forward strandPRRT1: 32,147,292–32,153,083, reverse strandPRRT1: 32,150,495–32,154,373, reverse strandPPT2-EGFL8: 32,153,845–32,171,978, forward strandEGFL8: 32,163,918–32,171,980, forward strandAGPAT1: 32,167,118–32,178,112, reverse strandRNF5: 32,178,391–32,184,769, forward strandAGER: 32,180,963–32,184,365, reverse strandPBX2: 32,184,733–32,190,278, reverse strandGPSM3: 32,190,766–32,195,523, reverse strandNOTCH4: 32,194,843–32,224,111, reverse strandNOTCH4TSBP1: 32,288,526–32,371,907, reverse strandTSBP1BTNL2: 32,391,481–32,407,181, reverse strandBTNL2HLA-DRA: 32,439,870–32,445,181, forward strandHLA-DRAHLA-DRB5: 32,516,622–32,530,369, reverse strandHLA-DRB5Diagram of CYP21A2: 10 exons on the forward strand of chromosome 6Exon 1: 1 known disease-causing siteExon 2: 2 known disease-causing sitesExon 4: 3 known disease-causing sitesExon 6: 2 known disease-causing sitesExon 7: 2 known disease-causing sitesExon 8: 6 known disease-causing sitesExon 10: 4 known disease-causing sitesExon 1: 32,038,415–32,038,624, 210 basesExon 2: 32,038,722–32,038,811, 90 basesExon 3: 32,039,094–32,039,248, 155 basesExon 4: 32,039,356–32,039,457, 102 basesExon 5: 32,039,546–32,039,647, 102 basesExon 6: 32,039,749–32,039,835, 87 basesExon 7: 32,040,005–32,040,205, 201 basesExon 8: 32,040,406–32,040,584, 179 basesExon 9: 32,040,668–32,040,771, 104 basesExon 10: 32,040,869–32,041,644, 776 bases123456789105′3′

Exons of the gene's MANE Select transcript (release v1.5), from NCBI and EMBL-EBI, on the GRCh38 reference genome.

Chromosome bands from UCSC's GRCh38 ideogram (2022-10-29).

Nearby genes from Ensembl release 116, on GRCh38.

Exons make up 2 kb of the gene's 3.2 kb; 1,488 of those bases code for the protein.

How a genome test reads CYP21A2

22

positions in CYP21A2 where ClinVar classes a change as pathogenic or likely pathogenic

22 of them (100%) fall in regions short reads find hard.

  • Low mappability (17 sites)Regions where 100 bp or 250 bp reads cannot be placed uniquely.
  • MHC (22 sites)The major histocompatibility complex (HLA genes), highly polymorphic and poorly represented by a single reference.
  • Segmental duplications (22 sites)Copies of at least 1 kb sharing at least 90% identity with another part of the genome (paralogues, pseudogenes); reads may align to the wrong copy.

A whole genome covers all 3.2 kb of CYP21A2, introns included, not only the 2 kb of exons.

Where this comes from

  • HGNC: the gene's symbol, name, other symbols and location.
  • MANE Select v1.5, from NCBI and EMBL-EBI: the transcript, its exons and coding sequence.
  • GenCC and ClinGen, released 2026-10-16: which conditions the gene is linked to, and how strongly.
  • The ACMG secondary findings list, SF v3.2.
  • ClinVar and the GIAB stratifications: known disease-causing sites, and the regions short reads find hard.
  • The Human Phenotype Ontology, release 2026-09-01: the traits linked to the gene. Find out more at hpo.jax.org.
  • Data release 2026.10.16-c6eea6bf.

Cite this page

APA

Dante Labs. (n.d.). CYP21A2 gene: cytochrome P450 family 21 subfamily A member 2. Retrieved 17 October 2026, from https://dantelabs.com/genes/cyp21a2

Vancouver

Dante Labs. CYP21A2 gene: cytochrome P450 family 21 subfamily A member 2 [Internet]. [cited 17 October 2026]. Available from: https://dantelabs.com/genes/cyp21a2

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