Hemoglobin H, Hemoglobin Variants

Hemoglobin is made up of heme (the iron-containing portion of hemoglobin) and globin (amino acid chains that form a protein). Hemoglobin (Hgb) molecules are found in all red blood cells. They bind oxygen in the lungs, carry the oxygen throughout the body, and release it to the body's cells and tissues. Hemoglobin H is a hemoglobin variant (abnormal form of hemoglobin) that occurs in some cases of alpha thalassemia. It is composed of four beta (β) globin chains and is created in response to a severe shortage of alpha (α) chains. Although each of the beta (β) globin chains is normal, the tetramer of 4 beta chains does not work normally. It has an increased affinity for oxygen, holding onto it instead of releasing it to the tissues and cells.

Normal hemoglobin types include:

  • Hemoglobin A (about 95% - 98%): Hgb A contains two alpha (α) chains and two beta (β) chains

  • Hgb A2 (2% - 3%): has two alpha (á) and two delta (ä) chains

  • Hgb F (up to 2%): the primary hemoglobin produced by the fetus during gestation; its production usually falls to a low level shortly after birth; Hgb F has two alpha (α) and two gamma (γ) chains

Hemoglobin variants are abnormal forms of hemoglobin that occur when changes (point mutations, deletions) in the globin genes cause changes in the amino acids that make up the globin protein. These changes may affect the structure of the hemoglobin, its behavior, its production rate, and/or its stability. Several hundred hemoglobin variants have been documented; however, only a few are common and clinically significant. The majority of these are beta chain variants.

These variants are inherited in an autosomal recessive fashion. A person inherits one copy of each beta globin gene from each parent. If one normal beta gene and one abnormal beta gene are inherited, the person is said to be a carrier or to be heterozygous for the abnormal hemoglobin. The abnormal gene can be passed on to any offspring but does not cause symptoms or health concerns in the carrier.

If two abnormal beta genes of the same type are inherited, the person is considered to have the disease and is homozygous for the abnormal hemoglobin. A copy of the abnormal beta gene will be passed on to any offspring.

If two abnormal beta genes of different types are inherited, the person is doubly or compound heterozygous. One of the abnormal beta genes will be passed on to each offspring.

MEANING OF TEST

Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.

OBTAINING THE TEST RESULTS

It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.