rare-and-clear

HBB hemoglobin subunit beta

Also known as: beta globin, beta-globin, HBB_HUMAN, hemoglobin beta gene, hemoglobin, beta, hemoglobin--beta locus.

Approximate pronunciation (generated from the name, not a recording):

What this gene does

The HBB gene provides instructions for making a protein called beta-globin. Beta-globin is a component (subunit) of a larger protein called hemoglobin, which is located inside red blood cells. In adults, hemoglobin typically consists of four protein subunits: two subunits of beta-globin and two subunits of a protein called alpha-globin, which is produced from another gene called HBA. Each of these protein subunits is attached (bound) to an iron-containing molecule called heme; the iron in the center of each heme can bind to one oxygen molecule. The hemoglobin within red blood cells binds to oxygen molecules in the lungs. The red blood cells then travel through the bloodstream and deliver oxygen to tissues throughout the body.

Source: MedlinePlus Genetics (reviewed 2024-03; source updated 2025-04-03).

More than one condition

Changes in this gene are associated with more than one condition: Sickle cell disease, Beta thalassemia. Each is described below.

Sickle cell disease

Approximate pronunciation (generated from the name, not a recording):

  • Sickle cell disease sickle cell disease

Also known as: HbS disease, Hemoglobin S disease, SCD, Sickle cell disorders, Sickling disorder due to hemoglobin S.

What is Sickle cell disease?

Sickle cell disease is a group of disorders that affects hemoglobin, the molecule in red blood cells that delivers oxygen to cells throughout the body. People with this disease have atypical hemoglobin molecules called hemoglobin S, which can distort red blood cells into a sickle or crescent shape.

Signs and symptoms of sickle cell disease usually begin in early childhood. Characteristic features of this disorder include a low number of red blood cells (anemia), repeated infections, and periodic episodes of pain. The severity of signs and symptoms varies from person to person. Some people have mild health issues, while others are frequently hospitalized for more serious complications.

The signs and symptoms of sickle cell disease are caused by the sickling of red blood cells. When red blood cells sickle, they break down prematurely, which can lead to anemia. Anemia can cause shortness of breath, fatigue, and delayed growth and development in children. The rapid breakdown of red blood cells may also cause yellowing of the skin and whites of the eyes (jaundice). Painful episodes can occur when sickled red blood cells, which are stiff and inflexible, get stuck in small blood vessels. These episodes deprive tissues and organs, such as the lungs, kidneys, spleen, and brain, of oxygen-rich blood and can lead to organ damage. A particularly serious complication of sickle cell disease is high blood pressure in the blood vessels that supply the lungs (pulmonary hypertension), which can lead to heart failure. Pulmonary hypertension occurs in about 10 percent of adults with sickle cell disease.

There are currently a range of treatment options for people with sickle cell disease. Some treatments address the symptoms of the condition, while others address the genetic cause of sickle cell disease and effectively cure the condition. Without treatment, individuals with sickle cell disease often have lifelong health problems.

Source: MedlinePlus Genetics (reviewed 2024-03; source updated 2025-04-03).

How it is inherited

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell must have a variant to cause the disorder. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they typically do not show signs and symptoms of the condition.

Source: MedlinePlus Genetics (reviewed 2024-03; source updated 2025-04-03).

How common it is

MedlinePlus Genetics Frequency

Sickle cell disease affects millions of people worldwide. It is most common among people whose ancestors come from Africa; Mediterranean countries such as Greece, Turkey, and Italy; the Arabian Peninsula; India; and Spanish-speaking regions in South America, Central America, and parts of the Caribbean.

Sickle cell disease is the most common inherited blood disorder in the United States, affecting an estimated 100,000 Americans. The disease is estimated to occur in 1 in 500 African Americans and 1 in 1,000 to 1,400 Hispanic Americans.

Source: MedlinePlus Genetics (reviewed 2024-03; source updated 2025-04-03).

Research studies

165 studies recruiting people with Sickle cell disease. Showing the first 5 of 165.

See all recruiting studies on ClinicalTrials.gov.

Source: ClinicalTrials.gov (retrieved 2026-10-04).

Beta thalassemia

Approximate pronunciation (generated from the name, not a recording):

  • Beta thalassemia beta thalassemia

Also known as: Erythroblastic anemia, Mediterranean anemia, Thalassemia, beta type.

What is Beta thalassemia?

Beta thalassemia is a blood disorder that reduces the production of hemoglobin. Hemoglobin is the iron-containing protein in red blood cells that carries oxygen to cells throughout the body.

In people with beta thalassemia, low levels of hemoglobin reduce oxygen levels in the body. Affected individuals also have a shortage of red blood cells (anemia), which can cause pale skin, weakness, fatigue, and more serious complications. People with beta thalassemia are at an increased risk of developing abnormal blood clots.

Beta thalassemia is classified into two types depending on the severity of symptoms: thalassemia major (also known as transfusion-dependent thalassemia or Cooley's anemia) and thalassemia intermedia (which is a non-transfusion-dependent thalassemia). Of the two types, thalassemia major is more severe.

The signs and symptoms of thalassemia major appear within the first 2 years of life. Children develop life-threatening anemia. They do not gain weight and grow at the expected rate (failure to thrive) and may develop yellowing of the skin and whites of the eyes (jaundice). Affected individuals may have an enlarged spleen, liver, and heart, and their bones may be misshapen. Puberty is delayed in some adolescents with thalassemia major.

Many people with thalassemia major have such severe symptoms that they need frequent blood transfusions to replenish their red blood cell supply. Over time, an influx of iron-containing hemoglobin from chronic blood transfusions can lead to a buildup of iron in the body, resulting in liver, heart, and hormone problems.

Thalassemia intermedia is milder than thalassemia major. The signs and symptoms of thalassemia intermedia appear in early childhood or later in life. Affected individuals have mild to moderate anemia and may also have slow growth, bone abnormalities, and an increased risk of developing abnormal blood clots.

Source: MedlinePlus Genetics (reviewed 2022-12; source updated 2025-04-03).

How it is inherited

Thalassemia major and thalassemia intermedia are inherited in an autosomal recessive pattern, which means both copies of the HBB gene in each cell have variants. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they typically do not show signs and symptoms of the condition. Sometimes, however, people with only one HBB gene variant in each cell develop mild anemia. These mildly affected people are said to have thalassemia minor.

In a small percentage of families, the HBB gene variant is inherited in an autosomal dominant manner. In these cases, one copy of the altered gene in each cell is sufficient to cause the signs and symptoms of beta thalassemia.

Source: MedlinePlus Genetics (reviewed 2022-12; source updated 2025-04-03).

How common it is

MedlinePlus Genetics Frequency

Beta thalassemia is a fairly common blood disorder worldwide. Thousands of infants with beta thalassemia are born each year. Beta thalassemia occurs most frequently in people from Mediterranean countries, North Africa, the Middle East, India, Central Asia, and Southeast Asia.

Source: MedlinePlus Genetics (reviewed 2022-12; source updated 2025-04-03).

Research studies

47 studies recruiting people with Beta thalassemia. Showing the first 5 of 47.

See all recruiting studies on ClinicalTrials.gov.

Source: ClinicalTrials.gov (retrieved 2026-10-04).

Family and care

What a diagnosis can mean for a family, and what to ask. This guidance is general, not specific to one gene.

What is a genetic consultation?

A genetic consultation is a health service that provides information and support to people who have, or may be at risk for, genetic conditions. During a consultation, a genetics professional meets with an individual or family to discuss genetic risks or to diagnose, confirm, or rule out a genetic condition.

Genetics professionals include medical geneticists (doctors who specialize in genetics) and genetic counselors (certified healthcare workers with experience in medical genetics and counseling). Other healthcare professionals such as nurses, psychologists, and social workers trained in genetics can also provide genetic consultations.

Consultations usually take place in a doctor’s office, hospital, genetics center, or other type of medical center. These meetings are most often in-person visits with individuals or families, but they are occasionally conducted in a group. Additionally, genetic consultations may be carried out using telemedicine (also known as telehealth), in which the meeting is done from a distance using computers, cameras, videoconferencing tools, or the telephone.

Source: MedlinePlus Genetics.

Why might someone have a genetic consultation?

Individuals or families who are concerned about an inherited condition may benefit from a genetic consultation. The reasons that a person might be referred to a genetic counselor, medical geneticist, or other genetics professional include:

A personal or family history of a genetic condition, birth defect, chromosomal disorder, or hereditary cancer.

Two or more pregnancy losses (miscarriages), a stillbirth, or a baby who died.

A child with a known inherited disorder, a birth defect, intellectual disability, or developmental delay.

A woman who is pregnant or plans to become pregnant at or after age 35. (Some chromosomal disorders occur more frequently in children born to older women.)

Abnormal test results that suggest a genetic or chromosomal condition.

An increased risk of developing or passing on a particular genetic disorder on the basis of a person’s ethnic background.

People related by blood (for example, cousins) who plan to have children together. (A child whose parents are related may be at an increased risk of inheriting certain genetic disorders.)

A person received results from direct-to-consumer genetic testing and they want to discuss the implications of the results.

A genetic consultation is also an important part of the decision-making process for genetic testing. A visit with a genetics professional may be helpful even if testing is not available for a specific condition, however.

Source: MedlinePlus Genetics.

What happens during a genetic consultation?

A genetic consultation provides information, offers support, and addresses a patient’s specific questions and concerns. To help determine whether a condition has a genetic component, a genetics professional asks about a person’s medical history and takes a detailed family health history (a record of health information about a person's immediate and extended family). The genetics professional may also perform a physical examination and recommend appropriate medical tests.

If a person is diagnosed with a genetic condition, the genetics professional provides information about the diagnosis, how the condition is inherited, the chance of passing the condition to future generations, and the options for testing and treatment.

During a consultation, a genetics professional will:

Interpret and communicate complex medical information.

Help each person make informed, independent decisions about their health care and reproductive options.

Respect each person’s individual beliefs, traditions, and feelings.

A genetics professional will NOT:

Tell a person which decision to make.

Coerce a couple about whether or not to have children.

Recommend that a woman continue or end a pregnancy.

Tell someone whether to undergo testing for a genetic disorder.

Source: MedlinePlus Genetics.

What is genetic counseling?

The goal of genetic counseling is to help you learn more about the causes of genetic conditions and how they affect you.

Genetic counselors can: Review your family and medical histories; Explain how genetic conditions are passed down through families; Figure out if you or your family members are at risk for disease; Find and give you information about genetic conditions; Offer guidance to help you make informed choices or life plans; Provide information about testing options and help you decide what is best for you and your family; Help you find referrals to medical specialists, advocacy and support networks, and other resources.

Source: National Society of Genetic Counselors and Genetic Alliance (CC BY; published 2008).

Where to go next

Words you may meet

Some technical words appear in the sections above and in the details below. Here is what they mean, in words from a public genetics glossary.

Gene
The gene is considered the basic unit of inheritance. Genes are passed from parents to offspring and contain the information needed to specify physical and biological traits. Most genes code for specific proteins, or segments of proteins, which have differing functions within the body. Humans have approximately 20,000 protein-coding genes. NHGRI Talking Glossary of Genomic and Genetic Terms
Chromosome
Chromosomes are threadlike structures made of protein and a single molecule of DNA that serve to carry the genomic information from cell to cell. In plants and animals (including humans), chromosomes reside in the nucleus of cells. Humans have 22 pairs of numbered chromosomes (autosomes) and one pair of sex chromosomes (XX or XY), for a total of 46. Each pair contains two chromosomes, one coming from each parent, which means that children inherit half of their chromosomes from their mother and half from their father. Chromosomes can be seen through a microscope when the nucleus dissolves during cell division. NHGRI Talking Glossary of Genomic and Genetic Terms
Autosomal Recessive Disorder
Autosomal recessive is a pattern of inheritance characteristic of some genetic disorders. “Autosomal” means that the gene in question is located on one of the numbered, or non-sex, chromosomes. “Recessive” means that two copies of the mutated gene (one from each parent) are required to cause the disorder. In a family where both parents are carriers and do not have the disease, roughly a quarter of their children will inherit two disease-causing alleles and have the disease. By contrast, an autosomal dominant disorder requires only a single copy of the mutated gene from one parent to cause the disorder. Sickle cell anemia is an example of an autosomal recessive genetic disorder. NHGRI Talking Glossary of Genomic and Genetic Terms
Autosomal Dominant Disorder
Autosomal dominant is a pattern of inheritance characteristic of some genetic disorders. “Autosomal” means that the gene in question is located on one of the numbered, or non-sex, chromosomes. “Dominant” means that a single copy of the mutated gene (from one parent) is enough to cause the disorder. A child of a person affected by an autosomal dominant condition has a 50% chance of being affected by that condition via inheritance of a dominant allele. By contrast, an autosomal recessive disorder requires two copies of the mutated gene (one from each parent) to cause the disorder. Huntington’s disease is an example of an autosomal dominant genetic disorder. NHGRI Talking Glossary of Genomic and Genetic Terms
Mitochondrial DNA
Mitochondrial DNA is the circular chromosome found inside the cellular organelles called mitochondria. Located in the cytoplasm, mitochondria are the site of the cell’s energy production and other metabolic functions. Offspring inherit mitochondria — and as a result mitochondrial DNA — from their mother. NHGRI Talking Glossary of Genomic and Genetic Terms
Genetic Imprinting
Genomic imprinting is the process by which only one copy of a gene in an individual (either from their mother or their father) is expressed, while the other copy is suppressed. Unlike genomic mutations that can affect the ability of inherited genes to be expressed, genomic imprinting does not affect the DNA sequence itself. Instead, gene expression is silenced by the epigenetic addition of chemical tags to the DNA during egg or sperm formation. Epigenetic tags on imprinted genes usually stay in place for the life of the individual. NHGRI Talking Glossary of Genomic and Genetic Terms
Protein
Proteins are large, complex molecules that play many important roles in the body. They are critical to most of the work done by cells and are required for the structure, function and regulation of the body’s tissues and organs. A protein is made up of one or more long, folded chains of amino acids (each called a polypeptide), whose sequences are determined by the DNA sequence of the protein-encoding gene. NHGRI Talking Glossary of Genomic and Genetic Terms
Mutation
A mutation is a change in the DNA sequence of an organism. Mutations can result from errors in DNA replication during cell division, exposure to mutagens or a viral infection. Germline mutations (that occur in eggs and sperm) can be passed on to offspring, while somatic mutations (that occur in body cells) are not passed on. NHGRI Talking Glossary of Genomic and Genetic Terms
Pathogenic Variant
A pathogenic variant is a genomic variant that may increase a person’s risk of developing a condition, disorder or disease. In many cases, carrying a pathogenic variant does not guarantee that a person will develop the specific condition but increases the risk for it. Pathogenic variants can be inherited from a parent or can occur spontaneously due to factors such as environmental exposure and aging. NHGRI Talking Glossary of Genomic and Genetic Terms
Genetic Testing
Genetic testing is the use of a laboratory test to examine an individual’s DNA for variations, typically performed in the context of medical care, ancestry studies or forensics. In a medical setting, the results of a genetic test can be used to confirm or rule out a suspected genetic disease. Results may also be used to determine the likelihood of parents passing on a genetic mutation to their offspring. Genetic testing may be performed prenatally or after birth. Genetic testing is also used to study the genomes of tumors in cancer cases. NHGRI Talking Glossary of Genomic and Genetic Terms
Carrier
A carrier, as related to genetics, is an individual who “carries” and can pass on to its offspring a genomic variant (allele) associated with a disease (or trait) that is inherited in an autosomal recessive or sex-linked manner, and who does not show symptoms of that disease (or features of that trait). The carrier has inherited the variant allele from one parent and a normal allele from the other parent. Any offspring of carriers is at risk of inheriting a variant allele from their parents, which would result in that child having the disease (or trait). NHGRI Talking Glossary of Genomic and Genetic Terms
Allele
An allele is one of two or more versions of DNA sequence (a single base or a segment of bases) at a given genomic location. An individual inherits two alleles, one from each parent, for any given genomic location where such variation exists. If the two alleles are the same, the individual is homozygous for that allele. If the alleles are different, the individual is heterozygous. NHGRI Talking Glossary of Genomic and Genetic Terms
Mendelian Inheritance
Mendelian inheritance refers to certain patterns of how traits are passed from parents to offspring. These general patterns were established by the Austrian monk Gregor Mendel, who performed thousands of experiments with pea plants in the 19th century. Mendel’s discoveries of how traits (such as color and shape) are passed down from one generation to the next introduced the concept of dominant and recessive modes of inheritance. NHGRI Talking Glossary of Genomic and Genetic Terms
Details you may see on a test report

These names and numbers are the technical ones doctors and labs use. You do not need to memorize them.

Location

This is where the gene sits on its chromosome, so you can match it to coordinates on a test report.

11p15.4 · GRCh38 chr11:5,225,464–5,229,395

Chromosome 11 ideogram with band 11p15.4 highlighted A simplified map of chromosome 11; the highlighted band marks where the gene sits.

Open in Ensembl (primary) or UCSC Genome Browser (secondary).

Source: HGNC (HGNC:4827).

Recommended transcript

This is the reference transcript labs use when they report a change in this gene.

MANE Select
NM_000518.5 (RefSeq) / ENST00000335295.4 (Ensembl)

Source: NCBI MANE.

Protein domains

These are the working parts of the protein, with the amino-acid positions each one covers.

  • Globin — amino acids 3–147

Source: InterPro (UniProt P68871).

Protein structure

This lets you look at the protein's 3D shape if you want to.

View the predicted structure in AlphaFold, or search the PDB for solved structures.

Source: UniProt (P68871).

Reported gene variants

ClinVar collects gene variants people have reported; it is a place to search, not a list on this page.

This page does not list individual variants. Search ClinVar for HBB instead.

Source: ClinVar.

What this page is not

This page is for education only. It is not medical advice, and it is not a diagnosis or a treatment plan. Talk with a doctor or a genetic counselor about your family's situation.