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HBA1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

HBA1 gene

The HBA1 gene provides instructions for producing alpha-globin, a critical component of hemoglobin, the protein responsible for transporting oxygen throughout the body.

Normal Function

The HBA1 gene provides instructions for making a protein called alpha-globin. This protein is also produced from a nearly identical gene called HBA2. These two genes are located close together on chromosome 16.

Alpha-globin is a subunit of hemoglobin, the protein in red blood cells that carries oxygen to cells and tissues. Hemoglobin is composed of four subunits: two alpha-globin subunits and two subunits of another type of globin. Each subunit carries an iron-containing molecule called heme, which is necessary for picking up oxygen in the lungs. A complete hemoglobin protein can carry four oxygen molecules at once.

Health Conditions Related to Genetic Changes

Alpha thalassemia

Alpha thalassemia is primarily caused by deletions of the HBA1 and/or HBA2 genes, though variants (mutations) can also occur. Because individuals have four alleles (two from each gene) that produce alpha-globin, the severity of the condition depends on how many alleles are lost or altered.

  • Hb Bart syndrome: The most severe form, resulting from the loss or alteration of all four alleles. It causes fluid buildup before birth (hydrops fetalis), severe anemia, and organ enlargement.
  • HbH disease: Usually caused by the loss of three alleles. It is characterized by mild to moderate anemia, jaundice, and organ enlargement.
  • Alpha thalassemia trait: Caused by the loss of two alleles; typically results in small, pale red blood cells and mild anemia.
  • Silent carriers: Caused by the loss of one allele; typically shows no signs or symptoms.

In severe cases, the shortage of alpha-globin leads to the production of abnormal hemoglobin (Hb Bart or HbH), which cannot effectively carry oxygen, resulting in anemia.

Other disorders

Alpha-thalassemia-intellectual disability syndrome (ATR-16) results from a large deletion on chromosome 16 that includes the HBA1 and HBA2 genes. In addition to alpha thalassemia trait, the loss of other nearby genes causes intellectual disability, delayed language skills, microcephaly, and distinctive facial features. Depending on the size of the deletion, it may also involve the PKD1 gene (leading to polycystic kidney disease) or the TSC2 gene (leading to tuberous sclerosis complex).

Other Names for This Gene

  • alpha 1 globin
  • alpha one globin
  • alpha-1 globin
  • alpha-1-globin
  • CD31
  • HBA-T3
  • HBA_HUMAN
  • hemoglobin alpha 1 globin chain
  • hemoglobin alpha-1 chain
  • hemoglobin, alpha 1
  • MGC126895
  • MGC126897

Frequently Asked Questions

If you are a silent carrier (one HBA1/HBA2 allele deleted), you typically have no symptoms. However, if your partner is also a carrier, there's a risk your children could inherit more deleted alleles, leading to more severe forms like alpha thalassemia trait, HbH disease, even Hb Bart syndrome (which is often fatal). Genetic counseling and partner screening are highly recommended to understand specific risks.
For alpha thalassemia trait, symptoms are often mild or absent, but may include mild anemia, fatigue, and pale skin. HbH disease is more severe, presenting with moderate to severe anemia, jaundice (yellowing of skin/eyes), an enlarged spleen or liver, and sometimes bone changes. These symptoms usually become noticeable in infancy or early childhood.
For milder forms like alpha thalassemia trait, specific dietary restrictions are generally not needed, but a balanced diet is important. Iron supplementation should be avoided unless specifically prescribed by a doctor, as iron overload can be a concern in some thalassemia types. Regular medical check-ups and avoiding certain oxidative stress-inducing medications (like some sulfa drugs) are also advised for HbH disease.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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