GENE REFERENCE / HGNC:2873

CYB5R3

cytochrome b5 reductase 3

protein-coding gene22q13.2Gene information

What does this gene do?

The CYB5R3 gene provides instruction for making an enzyme called cytochrome b5 reductase 3. This enzyme is involved in transferring negatively charged particles called electrons from one molecule to another. Two versions (isoforms) of this enzyme are produced from the CYB5R3 gene. The soluble isoform is present only in red blood cells, and the membrane-bound isoform is found in all other cell types.

Normal red blood cells contain molecules of iron-containing hemoglobin, which deliver oxygen to the body's tissues. The iron in hemoglobin is ferrous (Fe²⁺), but it can spontaneously become ferric (Fe³⁺). Hemoglobin that contains ferric iron is called methemoglobin, and it cannot deliver oxygen. The soluble isoform of cytochrome b5 reductase 3 changes ferric iron back to ferrous iron so hemoglobin can function. Normally, red blood cells contain less than 2 percent methemoglobin.

The membrane-bound isoform is embedded in the membranes of various cellular compartments and is widely used in the body. This isoform is necessary for many chemical reactions, including the breakdown and formation of fatty acids, the formation of cholesterol, and the breakdown of various molecules and drugs.

Source: MedlinePlus, National Library of Medicine. Source publication: 2023-03-21. Source review: 2015-05.

ClinGen reviews

ClinGen reviews the evidence linking a particular gene to a condition. Each rating below describes the strength of that link. It does not classify a variant in your DNA file.

Condition	Inheritance	Evidence
methemoglobinemia due to deficiency of methemoglobin reductaseMONDO:0009606 · Evaluated 2024-12-13	Autosomal recessive	DefinitiveGeneral Inborn Errors of Metabolism Gene Curation Expert Panel

ClinVar records

These numbers show what has been submitted to ClinVar. They cannot tell you how likely you are to have a condition.

Submitted alleles: 373
Submissions for variants in or overlapping this gene: 602
Submissions explicitly reporting this gene: 528
Alleles reported pathogenic / likely pathogenic: 41
VariationIDs with uncertain significance: 142
VariationIDs with conflicting classifications: 15

The rows count different things: alleles, submissions or VariationIDs. Their categories can overlap, so do not add them together. Pathogenic/likely pathogenic counts exclude structural variants that merely overlap a gene. A dash in the source means “not reported,” not zero.

NCBI produces the gene-summary file each week using counts recorded at the start of the month. The numbers may differ from those on the live ClinVar website. Read the field definitions ↗

View this gene in ClinVar ↗

YOUR DNA FILE

Can your DNA file tell you about CYB5R3?

From a DNA test kit (such as 23andMe, AncestryDNA or MyHeritage). These kits check a fixed list of about 600,000 to 700,000 positions across your whole genome. ClinVar lists 41 alleles in CYB5R3 reported as pathogenic or likely pathogenic. A kit checks only some of these positions, and often none of them.

From whole genome sequencing (a VCF file). Sequencing reads most of your genome. Your file lists the places where your DNA differs from the reference genome. Some regions are hard to sequence, including parts of some genes that have near-identical copies elsewhere, and a VCF file does not record which positions were read well.

If a variant is not in your file, that does not mean you don’t have it.

What BioDecode checks

BioDecode compares every variant in your file with ClinVar, on your own computer. For each match, it shows the ClinVar classification, the review status and the condition it was reported for. Your file is not uploaded.

A ClinVar classification applies to one particular variant and the condition it was reported for. It does not tell you about other variants in CYB5R3.

BioDecode cannot fill gaps in your test, diagnose a condition or replace clinical testing.

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