HBB

Official Full Name

hemoglobin subunit beta

Organism

Homo sapiens

GeneID

3043

Background

The alpha (HBA) and beta (HBB) loci determine the structure of the 2 types of polypeptide chains in adult hemoglobin, Hb A. The normal adult hemoglobin tetramer consists of two alpha chains and two beta chains. Mutant beta globin causes sickle cell anemia. Absence of beta chain causes beta-zero-thalassemia. Reduced amounts of detectable beta globin causes beta-plus-thalassemia. The order of the genes in the beta-globin cluster is 5'-epsilon -- gamma-G -- gamma-A -- delta -- beta--3'. [provided by RefSeq, Jul 2008]

Synonyms

ECYT6; CD113t-C; beta-globin;

Bio Chemical Class

Pore-forming globin

Protein Sequence

MVHLTPEEKSAVTALWGKVNVDEVGGEALGRLLVVYPWTQRFFESFGDLSTPDAVMGNPKVKAHGKKVLGAFSDGLAHLDNLKGTFATLSELHCDKLHVDPENFRLLGNVLVCVLAHHFGKEFTPPVQAAYQKVVAGVANALAHKYH

Open

Disease

Sickle-cell disorder, Thalassaemia

Approved Drug

Clinical Trial Drug

3 +

Discontinued Drug

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Detailed Information

Hemoglobin is a complex protein responsible for carrying oxygen within red blood cells. The adult form, referred to as Hb A, consists of two types of polypeptide chains: alpha (HBA) and beta (HBB). Each hemoglobin molecule is a tetramer, composed of two alpha chains and two beta chains. These chains create a pocket that holds heme, a molecule containing iron, which binds oxygen. This structural formation allows hemoglobin to efficiently transport oxygen from the lungs to peripheral tissues.

The gene coding for the beta subunit, known as HBB, is found on chromosome 11. Its order in the beta-globin cluster is 5'-epsilon -- gamma-G -- gamma-A -- delta -- beta--3'. Variations in this gene can lead to significant health conditions. A point mutation in the sixth amino acid position of the HBB gene results in sickle cell anemia, where glutamine is replaced by valine. This substitution leads to the formation of sickle-shaped red blood cells due to polymerization of the deoxygenated sickle hemoglobin. Conversely, deficiencies in beta-globin production can cause beta-thalassemia, a hereditary blood disorder classified into beta-zero-thalassemia and beta-plus-thalassemia depending on the level of beta chain synthesis reduction.

HBB is not only crucial for oxygen transport but is also implicated in certain drug toxicities. In research, HBB has been shown to interact with ac (aconitine), a compound that can induce cardiac toxicity through binding with HBB and affecting cardiomyocyte survival. Moreover, manipulation of HBB expression has been observed to alter toxic reactions in cells, marking it as a vital biomarker for assessing individual sensitivity to specific drugs.

Figure 1 describes genetic alterations in the HBB gene, detailing how mutations such as the substitution in the sickle Hb (HbS) allele lead to conditions like sickle cell disease (SCD) and various HbS-related syndromes, illustrating their genetic basis, geographic prevalence, and clinical implications. Figure 1. Genetic alterations in HBB. (Rees DC, et al., 2010)

Sickle Cell Disease and Beta-Thalassemia

Sickle cell disease arises from the mutation of the beta-globin chain, leading to the production of sickle hemoglobin. These hemoglobin molecules clump together at low oxygen levels to create stiff polymers that transform red blood cells into a sickle form. Known as chronic hemolysis, this deformation causes cells to become prone to rupture, hence shortening their normal 110-120 day lifetime to around 10-20 days. Over time, the ensuing anemia and blood artery blockage may lead to severe problems including organ damage, stroke, and chest syndrome.

Mutations that damage beta-globin production produce beta-thalassemia, which results in low hemoglobin synthesis. It shows in several degrees: mild, middle, and significant. People with little beta-thalassemia usually show no symptoms but might have little anemia seen only by blood testing. Intermediate and major types show more significant anemia that needs medical treatment such as consistent blood infusions. Untreated, major beta-thalassemia—known as Cooley's anemia—can cause notable physiological and developmental problems.

Hematopoietic stem cell transplantation—bone marrow transplant—is the only current cure, but it is expensive, and donor compatibility limits availability. Most patients rely on frequent blood transfusions, so this approach has dangers including iron overload that need chelation treatment to avoid organ damage. Aiming to enhance patient outcomes and quality of life, advances in gene therapy and new medication inventions are underway to provide alternative therapies for beta-thalassemia and sickle cell disease.

Advances and Challenges in Genetic Research

The study of HBB and related globin genes has illuminated new pathways for understanding hemoglobinopathies and their management. Research into genetic modifiers and their role in disease severity is crucial for developing personalized medicine approaches. These efforts aim to tailor treatments based on an individual's genetic makeup, potentially minimizing disease impact and improving therapeutic efficacy.

Innovations in drug development focus on modulating hemoglobin synthesis and function. Researchers are exploring gene editing techniques, such as CRISPR, to correct genetic defects at their source. Additionally, investigations into novel pharmacological agents seek to induce fetal hemoglobin production, which can ameliorate symptoms of beta-thalassemia and sickle cell disease. These strategies hold promise for transforming the therapeutic landscape in hematology.

Continued exploration of beta-globin gene variants helps to refine diagnostic tools and determine disease prognosis. The relationship between beta-globin mutations and clinical outcomes emphasizes the importance of early diagnosis and intervention. As understanding of HBB-related conditions deepens, integrating genetic data with clinical practice will likely enhance disease management and patient care. Addressing challenges such as treatment accessibility and affordability remains essential in the quest for comprehensive global healthcare solutions.

References:

Rees DC, Williams TN, Gladwin MT. Sickle-cell disease. Lancet. 2010;376(9757):2018-2031.
Park SH, Bao G. CRISPR/Cas9 gene editing for curing sickle cell disease. Transfus Apher Sci. 2021;60(1):103060.
Harteveld CL, Achour A, Arkesteijn SJG, et al. The hemoglobinopathies, molecular disease mechanisms and diagnostics. Int J Lab Hematol. 2022;44 Suppl 1(Suppl 1):28-36.

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