Hemoglobin Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobin ...

is a protein that transports oxygen in the blood. Genetic differences lead to structural variants in the hemoglobin protein structure. Some variants can cause disease while others have little to no effect. The normal hemoglobin types are Hemoglobin A (HbA), which makes up 95–98% of total hemoglobin in adults, Hemoglobin A2 (HbA2), which constitutes 2–3% of total hemoglobin in adults, and Hemoglobin F (HbF), which is the predominant hemoglobin in the fetus during pregnancy, and may persist in small amounts in adults. Hemoglobin variants occur when there are mutations in specific genes that code for the protein chains, known as globins, which make up the hemoglobin molecule. This leads to

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

substitutions in the hemoglobin molecule that could affect the structure, properties, and/or the stability of the hemoglobin molecule. There are over 1,000 naturally occurring structural variants of

hemoglobin Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobin ...

in humans.

Effects of variants

The physiological effects of these variants can range from minor to severe. Mutations can caused impaired production of hemoglobin (

thalassemia Thalassemias are a group of Genetic disorder, inherited blood disorders that manifest as the production of reduced hemoglobin. Symptoms depend on the type of thalassemia and can vary from none to severe, including death. Often there is mild to ...

) or produce structurally altered hemoglobins. Some hemoglobin variants, such as HbS which causes sickle-cell anemia, are responsible for severe diseases and are considered hemoglobinopathies. Other variants cause no detectable

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, and are thus considered non-pathological variants.

Discovery of variants

Hemoglobin variants can be discovered through examination, routine laboratory testing, or evaluation of patients with severe anemia. In some countries, all newborns are tested for hemoglobinopathies, thalassemias, and HbS. Isoelectric focusing or

high-performance liquid chromatography High-performance liquid chromatography (HPLC), formerly referred to as high-pressure liquid chromatography, is a technique in analytical chemistry used to separate, identify, and quantify specific components in mixtures. The mixtures can origin ...

are used to identify structural abnormalities in hemoglobin.

Examples of variants

There are in excess of 1,000 known hemoglobin variants. A research database of hemoglobin variants is maintained by

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. A few of these variants are listed below.

Normal hemoglobins

;Embryonic * HbE Gower 1 (ζ₂ε₂) * HbE Gower 2 (α₂ε₂) * HbE Portland I (ζ₂γ₂) * HbE Portland II (ζ₂β₂) ;Fetal * HbF/Fetal (α₂γ₂) * HbA (α₂β₂) ;Adult * HbA (α₂β₂) * HbA₂ (α₂δ₂) * HbF/Fetal (α₂γ₂)

Pathologic/abnormal hemoglobins

Relatively common

Source: * HbS (α₂β^S₂) * HbC (α₂β^C₂) * HbE (α₂β^E₂)

Less frequent

* HbH (β₄) * Hb Barts (γ₄) *

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(α₂β^O₂) * Hb Bassett * Hb Kansas * Hb D-Punjab * Hb O-Arab * Hb G-Philadelphia * Hb Hasharon * Hb Kirklareli * Hb Lepore * Hb M * Hb Hope * Hb Pisa * Hb J * Hb N-Baltimore * Hemoglobin Chesapeake * Hemoglobin Louisville * Hemoglobin Vanvitelli

References

External links

A syllabus of hemoglobin variants
{{Hemeproteins Red blood cell disorders Genetic disorders with no OMIM Hemoglobins Respiratory physiology