HBB rs33945777: Understanding the IVS-I-110 G>A Variant
The HBB rs33945777 variant, also known as IVS-I-110 G>A, is a genetic change in the HBB gene that affects how the body produces beta-globin. It is primarily associated with beta-plus thalassemia, a condition that reduces the production of hemoglobin in red blood cells.
What each genotype means
Typical beta-globin function
This genotype represents the common, functional version of the HBB gene. Individuals with this profile do not carry the specific IVS-I-110 G>A mutation associated with beta-thalassemia.
This is the most common genotype observed in the general population.
Beta-thalassemia carrier status
This genotype indicates you carry one copy of the IVS-I-110 G>A mutation, which can lead to reduced production of beta-globin protein. Carriers are typically asymptomatic but may experience mild anemia, and should discuss these results with a genetic counselor or clinician to understand reproductive risks.
This variant is most frequently observed in individuals of Mediterranean and Middle Eastern ancestry.
Beta-thalassemia major
This genotype indicates the presence of two copies of the IVS-I-110 G>A mutation, which significantly impairs the production of functional beta-globin. This condition is associated with beta-thalassemia, which may result in severe anemia and a potential requirement for regular medical interventions such as blood transfusions.
This genotype is rare and primarily found in populations where the carrier frequency of this specific HBB mutation is elevated.
What is the rs33945777 Variant?
The rs33945777 variant is a single nucleotide change located within the HBB gene on chromosome 11. Specifically, it is a splice junction mutation, often referred to in medical literature as IVS-I-110 G>A. This means the change occurs at a critical site where the cell's machinery processes the genetic instructions for building proteins. By altering this splice site, the variant interferes with the correct assembly of messenger RNA (mRNA), which is the blueprint for the beta-globin protein. When the splicing process is disrupted, the cell may produce less functional beta-globin, or in some cases, abnormal versions of the protein. This variant is frequently included in expanded carrier screening panels because it is a well-documented cause of reduced beta-globin production.
The Role of the HBB Gene
The HBB gene provides instructions for making a protein called beta-globin, which is a vital component of hemoglobin. Hemoglobin is the protein in red blood cells that carries oxygen from the lungs to the rest of the body. A functional hemoglobin molecule is typically composed of two alpha-globin subunits and two beta-globin subunits. When mutations occur in the HBB gene, they can lead to a group of blood disorders known as beta-thalassemia. These disorders are characterized by a reduced or absent production of beta-globin, which in turn leads to a shortage of healthy red blood cells and can cause anemia. The severity of the condition often depends on whether one or both copies of the HBB gene are affected by a mutation.
Research and Clinical Associations
Research has consistently associated the rs33945777 variant with beta-plus thalassemia, a form of the condition where beta-globin production is reduced but not entirely absent. Clinical evidence, including data from databases like ClinVar, classifies this variant as pathogenic in the context of thalassemia. It is important to note that the clinical impact can vary significantly based on an individual's overall genetic background and the presence of other HBB variants. While the association with beta-thalassemia is well-established in scientific literature, the specific health outcomes for an individual can range from mild anemia to more significant clinical needs. Because this is a carrier-status variant, it is primarily discussed in the context of family planning and genetic counseling to understand the risk of passing the trait to offspring.
Population Frequency
The rs33945777 variant is not evenly distributed across the globe. It is most frequently observed in populations from the Eastern Mediterranean and the Middle East. In these regions, the variant is considered a common cause of beta-thalassemia. Because of this specific geographic distribution, individuals with ancestry from these areas are more likely to be screened for this variant during preconception or prenatal testing. In other global populations, the frequency of this specific mutation is significantly lower. Understanding one's ancestral background can be a helpful context when interpreting the results of genetic screening, as it explains why certain variants are more prevalent in specific groups than in the general global population.
Interpreting Your Genetic Information
If you have received information about your status regarding rs33945777, it is essential to understand that this is a carrier-status finding. Being a carrier typically means you have one copy of the variant and one typical copy of the gene, which usually does not result in significant health issues for the carrier themselves. However, if both parents are carriers of HBB variants, there is a risk of having a child with a more severe form of thalassemia. This information should not be used for self-diagnosis or to make medical decisions. If you have questions about your carrier status or what it means for your family, you should consult with a genetic counselor or a healthcare provider who specializes in hematology or medical genetics. They can provide personalized guidance based on your full clinical and genetic profile.
How common is this variant?
The rs33945777 variant is enriched across Eastern Mediterranean and Middle Eastern populations, with a minor allele frequency of approximately 0.01 in regional cohorts.
Frequently asked questions
What is the HBB gene?
The HBB gene provides instructions for making beta-globin, a protein that is a key component of hemoglobin. Hemoglobin is responsible for carrying oxygen in your red blood cells.
Is rs33945777 the same as IVS-I-110?
Yes, rs33945777 is the identifier used in genetic databases for the IVS-I-110 G>A mutation. It is a well-known splice junction variant in the HBB gene.
What does it mean to be a carrier of beta-thalassemia?
Being a carrier means you have one copy of a mutation in the HBB gene. Carriers typically do not have severe symptoms but can pass the variant to their children.
Should I be worried if I have this variant?
Carrier status is common and often does not cause health problems. You should discuss your results with a genetic counselor to understand the implications for your health and family planning.
Sources & further reading
Educational information only, last refreshed 9/28/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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This variant is a pathogenic mutation in the HBB gene associated with beta-thalassemia.
This variant is a pathogenic mutation in the HBB gene associated with hemoglobinopathies such as sickle cell disease.
This variant (c.20A>T, p.Glu7Val) causes the substitution of valine for glutamic acid in the beta-globin chain, leading to sickle cell trait or disease depending on zygosity.
Pathogenic variant (p.Glu6Val, HbS-Antilles) in HBB associated with sickle cell disease-like pathology.
Pathogenic nonsense mutation (c.118C>T / p.Gln40Ter / codon 39 nonsense) causing beta-zero thalassemia and classic carrier status (beta-thalassemia minor).
This variant, known as Hb C-Harlem, involves a double mutation in the HBB gene that can lead to sickle-beta-thalassemia-like phenotypes.