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Gene

CYB5A

cytochrome b5 type A

Summary

Cytogenetic location
18q22.3
Coordinates
Chromosome 18: 74,250,846–74,291,963 (GRCh38)
Exons
5 exons across 41.1 kb
Protein
134 amino acids
Also known as
MCB5
Previous symbols
CYB5
MANE Select transcript
ENST00000340533.9NM_148923.4
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

  • Hereditary Methaemoglobinaemia and Unstable Haemoglobins

    • Hereditary Methaemoglobinaemia

      Raised methaemoglobin levels from birth, caused by recessive changes in CYB5R3 or CYB5A or by dominant haemoglobin M variants in the globin genes; type II CYB5R3 deficiency also causes severe developmental problems.

      • ClinGen rates the link definitive
      • 2 GenCC submitters rate it definitive or strong
      What knowing changes

      Knowing about it explains unexplained cyanosis and helps avoid medicines that raise methaemoglobin, such as dapsone, benzocaine and nitrites; methylene blue treats the enzyme forms but must not be given to people with G6PD deficiency.

How CYB5A is laid out

  • Coding sequence
  • Untranslated region
  • Intron
  • Direction of transcription
  • Known disease-causing sites
  • Stretches short reads find hard
Chromosome 18, with a bracket where CYB5A sits. CYB5A and 7 genes near it on chromosome 18, from 73,771,405 to 74,771,404.Chromosome 1818q22.3p11.32p11.31p11.23p11.22p11.21p11.1q11.1q11.2q12.1q12.2q12.3q21.1q21.2q21.31q21.32q21.33q22.1q22.2q22.3q2373.8 Mb74 Mb74.2 Mb74.4 Mb74.6 MbFBXO15: 74,073,344–74,147,867, reverse strandFBXO15TIMM21: 74,148,512–74,160,531, forward strandTIMM21CYB5A: 74,250,846–74,291,963, reverse strandCYB5AC18orf63: 74,315,839–74,359,189, forward strandC18orf63DIPK1C: 74,434,101–74,457,944, reverse strandDIPK1CCNDP2: 74,494,112–74,523,561, forward strandCNDP2CNDP1: 74,534,400–74,594,850, forward strandCNDP1ZNF407: 74,597,848–75,065,671, forward strandZNF407Diagram of CYB5A: 5 exons on the reverse strand of chromosome 18Exon 2: 1 known disease-causing siteExon 1: 1 known disease-causing siteExon 5: 74,250,846–74,253,665, 2,820 basesExon 4: 74,255,741–74,255,775, 35 basesExon 3: 74,260,915–74,260,944, 30 basesExon 2: 74,263,349–74,263,477, 129 basesExon 1: 74,291,747–74,291,963, 217 bases543215′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 3.2 kb of the gene's 41.1 kb; 405 of those bases code for the protein.

How a genome test reads CYB5A

2

positions in CYB5A where ClinVar classes a change as pathogenic or likely pathogenic

None of them falls in a region short reads find hard.

A whole genome covers all 41.1 kb of CYB5A, introns included, not only the 3.2 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.). CYB5A gene: cytochrome b5 type A. Retrieved 16 October 2026, from https://dantelabs.com/genes/cyb5a

Vancouver

Dante Labs. CYB5A gene: cytochrome b5 type A [Internet]. [cited 16 October 2026]. Available from: https://dantelabs.com/genes/cyb5a

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