Types in humans




Hemoglobin variants are a part of the normal embryonic and fetal development. They may also be pathologic mutant forms of hemoglobin in a population, caused by variations in genetics. Some well-known hemoglobin variants, such as sickle-cell anemia, are responsible for diseases and are considered hemoglobinopathies. Other variants cause no detectable pathology, and are thus considered non-pathological variants.

In the embryo:

  • Gower 1 (ζ2ε2)
  • Gower 2 (α2ε2) (PDB: 1A9W​)
  • Hemoglobin Portland I (ζ2γ2)
  • Hemoglobin Portland II (ζ2β2).

In the fetus:

  • Hemoglobin F (α2γ2) (PDB: 1FDH​).

After birth:

  • Hemoglobin A (adult hemoglobin) (α2β2) (PDB: 1BZ0​) – The most common with a normal amount over 95%
  • Hemoglobin A2 (α2δ2) – δ chain synthesis begins late in the third trimester and, in adults, it has a normal range of 1.5–3.5%
  • Hemoglobin F (fetal hemoglobin) (α2γ2) – In adults Hemoglobin F is restricted to a limited population of red cells called F-cells. However, the level of Hb F can be elevated in persons with sickle-cell disease and beta-thalassemia.

Variant forms that cause disease:

  • Hemoglobin D-Punjab – (α2βD2) – A variant form of hemoglobin.
  • Hemoglobin H (β4) – A variant form of hemoglobin, formed by a tetramer of β chains, which may be present in variants of α thalassemia.
  • Hemoglobin Barts (γ4) – A variant form of hemoglobin, formed by a tetramer of γ chains, which may be present in variants of α thalassemia.
  • Hemoglobin S (α2βS2) – A variant form of hemoglobin found in people with sickle cell disease. There is a variation in the β-chain gene, causing a change in the properties of hemoglobin, which results in sickling of red blood cells.
  • Hemoglobin C (α2βC2) – Another variant due to a variation in the β-chain gene. This variant causes a mild chronic hemolytic anemia.
  • Hemoglobin E (α2βE2) – Another variant due to a variation in the β-chain gene. This variant causes a mild chronic hemolytic anemia.
  • Hemoglobin AS – A heterozygous form causing sickle cell trait with one adult gene and one sickle cell disease gene
  • Hemoglobin SC disease – A compound heterozygous form with one sickle gene and another encoding Hemoglobin C.
  • Hemoglobin Hopkins-2 - A variant form of hemoglobin that is sometimes viewed in combination with Hemoglobin S to produce sickle cell disease.

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