Hemoglobin - Types in Humans

Types in Humans

Hemoglobin variants are a part of the normal embryonic and fetal development, but 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 (ζ₂γ₂).

In the fetus:

• Hemoglobin F (α₂γ₂) (PDB 1FDH).

In adults:

• Hemoglobin A (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 (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 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.