What you carry at this position in your DNA and what research says about it.
Thalassemia and Anemia Risk: 10/10 evidence, 18 publications.
You're viewing every possible genotype for this variant.
None of these is your result. Use the genotype toggle to compare them, then sign up and upload your DNA to see which one is yours.
Sample genotype (not yours): G/G
Typical Hemoglobin Production and Low Thalassemia Risk
Two standard copies of the gene ensure normal production of beta-globin proteins. This genotype protects against inherited beta thalassemia and related severe blood disorders.
What this genotype means: Normal hemoglobin levels; Typical red blood cell size; No risk of transmitting beta-zero thalassemia.
Sample genotype (not yours): A/A
High Risk of Severe Beta Thalassemia Major
A complete absence of functional beta-globin occurs when this mutation is inherited from both parents. This leads to severe, life-threatening anemia requiring lifelong medical management.
What this genotype means: Severe life-threatening anemia; Absence of functional beta-globin; Requirement for lifelong medical treatment.
Sample genotype (not yours): G/A
Beta Thalassemia Carrier with Mild Anemia Risk
One copy of the mutation reduces the production of functional beta-globin. This typically causes mild anemia but provides carrier status for beta thalassemia.
What this genotype means: Mild chronic anemia; Smaller red blood cells; Carrier status for beta thalassemia major.
Gene function and biological role
Gene Function: The HBB gene provides instructions for making a protein called beta-globin [1]. Beta-globin is an essential component of hemoglobin, the protein in red blood cells that carries oxygen throughout the body [1]. Normal hemoglobin consists of four protein subunits, including two beta-globins and two alpha-globins [1]. Mutations in the HBB gene can disrupt the production or structure of beta-globin, leading to various blood disorders [2]. These disorders include beta thalassemia and sickle cell disease, which impair oxygen transport and cause anemia [2].
Variant Impact: A premature stop signal is introduced into the HBB gene by this specific genetic change, known as the codon 39 nonsense mutation [1]. The premature stop signal prevents the cell from producing full-length, functional beta-globin protein [1]. Instead, the abnormal genetic message is typically destroyed by the cell's quality control systems before it can be translated [2]. This complete lack of beta-globin production is classified as a beta-zero mutation [1]. It is one of the most common genetic causes of beta thalassemia in Mediterranean populations [1].
Key Insight: This variant is a major cause of beta thalassemia in Mediterranean regions, particularly Sardinia, where it has been studied extensively.
Location: HBB. Chromosome 11 · 11p15.4 · 5.2 Mb
Origin Story: Carrying a single copy of a beta thalassemia mutation provides partial protection against severe malaria infections, which historically kept this mutation in the gene pool in malaria-prone regions like the Mediterranean.
Estimated prevalence by population
Global 99.9%; European 99.9%; African 100.0%; East Asian 100.0%; South Asian 100.0%; Americas 99.9%; Ashkenazi 100.0%; Finnish 100.0%; Middle Eastern 100.0%; Amish 100.0%.
Estimated GG genotype frequency.
Global 0.1%; European 0.1%; African 0.0%; East Asian 0.0%; South Asian 0.0%; Americas 0.1%; Ashkenazi 0.0%; Finnish 0.0%; Middle Eastern 0.0%; Amish 0.0%.
Estimated GA genotype frequency.
Global < 0.1%; European < 0.1%; African 0.0%; East Asian 0.0%; South Asian 0.0%; Americas < 0.1%; Ashkenazi 0.0%; Finnish 0.0%; Middle Eastern 0.0%; Amish 0.0%.
Estimated AA genotype frequency.
Showing effects for G/G genotype
Rare Genetic Disorders
Hemoglobinopathies
Thalassemia. Evidence: 7/10. Source: PMID 6457059. Typical Risk.
Cardiovascular & Metabolic
Blood Cell & Iron Traits
Anemia. Evidence: 10/10. Source: PMID 39024449. Typical Risk.
Hemoglobin Levels. Evidence: 10/10. Source: PMID 33887194. Typical Levels.
Lipids & Cholesterol
Cholesterol Levels. Evidence: 10/10. Source: PMID 33339817. Slightly Higher.
Showing effects for A/A genotype
Thalassemia. Evidence: 7/10. Source: PMID 6457059. High Risk.
Anemia. Evidence: 10/10. Source: PMID 39024449. High Risk.
Hemoglobin Levels. Evidence: 10/10. Source: PMID 33887194. Extremely Low.
Cholesterol Levels. Evidence: 10/10. Source: PMID 33339817. Lower.
Showing effects for G/A genotype
Thalassemia. Evidence: 7/10. Source: PMID 6457059. Elevated Carrier Risk.
Anemia. Evidence: 10/10. Source: PMID 39024449. Slightly Increased.
Hemoglobin Levels. Evidence: 10/10. Source: PMID 33887194. Lower Levels.
Cholesterol Levels. Evidence: 10/10. Source: PMID 33339817. Typical.
What this genotype means for the people who carry it
Sample genotype: GG (Homozygous)
Standard hemoglobin production relies on having two functional copies of the HBB gene to build beta-globin subunits [1]. Lacking the codon 39 mutation means the body successfully manufactures healthy red blood cells with optimal oxygen-carrying capacity [1]. Clinical studies show that this common genotype is associated with normal hemoglobin levels and typical red blood cell counts [2]. While cholesterol levels may be slightly higher compared to carriers of the mutation, overall cardiovascular and hematological health remains within the typical range [3]. There is no risk of passing on beta-zero thalassemia to offspring from this genetic locus [1].
Normal hemoglobin levels; Typical red blood cell size; No risk of transmitting beta-zero thalassemia.
Sample genotype: AA (Homozygous)
Inheriting two copies of this premature stop mutation results in a complete absence of functional beta-globin protein [1]. This severe condition is known as beta thalassemia major or Cooley's anemia [1]. Without functional beta-globin, the body cannot form normal hemoglobin, leading to the rapid destruction of red blood cells [2]. Symptoms of severe anemia, fatigue, and bone complications typically appear within the first two years of life [2]. Regular blood transfusions and iron chelation therapy are standard medical interventions required to manage this condition [1].
Severe life-threatening anemia; Absence of functional beta-globin; Requirement for lifelong medical treatment.
Sample genotype: GA (Heterozygous)
Having one mutated copy of the gene means the body produces less functional beta-globin than typical [1]. This condition is widely known as beta thalassemia minor or beta thalassemia trait [1]. While most carriers live normal, healthy lives, they often experience mild, lifelong anemia and smaller-than-average red blood cells [2]. Routine blood tests frequently show reduced hemoglobin levels and altered red cell distribution width [2]. If both parents carry this mutation, there is a twenty-five percent chance their child will inherit beta thalassemia major [1].
Mild chronic anemia; Smaller red blood cells; Carrier status for beta thalassemia major.
Variants with shared genetic architecture
rs33930165 · HBB Gene · Chr 11 · Hemoglobin C Status
rs33946267 · HBB Gene · Chr 11 · Hemoglobin D Disease Risk
rs334 · HBB Gene · Chr 11 · Sickle Cell Status
beta zero thalassemia in Sardinia is caused by a nonsense mutation.
Diversity and scale: Genetic architecture of 2068 traits in the VA Million Veteran Program.
Mutational Profile of Homozygous β-Thalassemia in Rio de Janeiro, Brazil.
Content updated August 2026.
ReadYourDNA provides educational interpretation of DNA data you already have. It is not diagnostic, not a substitute for professional medical advice, diagnosis, or treatment, and is not intended to diagnose, treat, cure, or prevent any disease. Talk to a clinician before acting on any result.
Raw DNA Data Reports for 23andMe & AncestryDNA · About ReadYourDNA · FAQ · Methodology & Science · Pricing · Support and complaints · Legal & Contact · Health Traits · Pharmacogenomics · Carrier Status · Variant Explorer · The Human Karyotype · Privacy Policy · Terms of Service · Accessibility · Consumer Health Data Privacy · Your Privacy Choices · Editorial Standards · Your Data, Checkable · Sample Report · ReadYourDNA and Promethease compared · What is inside a 23andMe raw data file · What is inside an AncestryDNA raw data file · What a chatbot can and cannot do with your raw DNA file · Where a raw DNA file can still be uploaded in 2026
Written, maintained and operated by Martin Pechhacker, sole proprietor, Vienna, Austria. Trade register GISA 40064420. support@readyourdna.com