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Trait

Methemoglobinemia

Abnormally increased levels of methemoglobin in the blood. In this form of hemoglobin, there is an oxidized ferric iron (Fe +3) rather than the reduced ferrous form (Fe 2+) that is normally found in hemoglobin. Methemoglobin has a reduced affinity for oxygen, resulting in a reduced ability to release oxygen to tissues.

HPO HP:0012119

Summary

Body system
Abnormality of blood and blood-forming tissues

6 genes linked to Methemoglobinemia

Changes in these genes cause rare conditions in which Methemoglobinemia is seen. Most people with this trait have none of those conditions, and a gene on this list says nothing about anyone's own genome.

GeneHow often it is seenConditions
CYB5Acytochrome b5 type AAlwaysIn 2 conditions
CYB5R3cytochrome b5 reductase 3AlwaysIn 2 conditions
HBG2hemoglobin subunit gamma 2AlwaysIn 1 condition
HGDhomogentisate 1,2-dioxygenaseSometimes (5–29%)In 1 condition
HBA1hemoglobin subunit alpha 1Not recordedIn 1 condition
HBBhemoglobin subunit betaNot recordedIn 1 condition

How often is among people with one of the gene's conditions, the most often across them, as the Human Phenotype Ontology records it. These pages describe traits and the research behind them; they are not a diagnosis, and a doctor or genetic counsellor is the person to ask about symptoms.

Broader traits

Abnormal hemoglobin

Where this comes from

  • The Human Phenotype Ontology, release 2026-09-01: the trait, its names, its definition and the genes linked to it. Find out more at hpo.jax.org.
  • Data release 2026.10.16-c6eea6bf.

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