IFNL3 rs12975333: What Your Genotype Means
The rs12975333 variant is a single nucleotide polymorphism located near the IFNL3 gene on chromosome 19. It is widely studied for its statistical association with the body's ability to spontaneously clear hepatitis C virus (HCV) infections and respond to certain antiviral treatments.
What each genotype means
Favorable HCV clearance profile
This genotype is associated with a higher likelihood of spontaneously clearing a hepatitis C virus (HCV) infection compared to other genotypes. Research suggests this variant influences the body's interferon response, which plays a role in how the immune system manages viral infections. If you have concerns about viral infections or liver health, please discuss your medical history and any relevant testing with your clinician.
The frequency of this genotype varies significantly by ancestry, being most common in individuals of East Asian descent and less common in those of African ancestry.
Intermediate HCV clearance profile
This genotype is associated with an intermediate likelihood of spontaneously clearing a hepatitis C virus (HCV) infection. The biological mechanism involves the IFNL3/IFNL4 region, which helps regulate the immune system's response to viral pathogens. Please consult with your healthcare provider to discuss your specific health context and any necessary screenings.
This heterozygous genotype is found at varying frequencies globally, often representing a significant portion of the population in many diverse ethnic groups.
Reduced HCV clearance profile
This genotype is associated with a lower likelihood of spontaneously clearing a hepatitis C virus (HCV) infection compared to the CC genotype. This association is linked to the regulation of the IFNL4 gene, which can influence the liver's inflammatory response to the virus. If you have questions about your liver health or viral risk, please discuss them with your clinician or a specialist.
This genotype is more frequently observed in individuals of African ancestry compared to those of European or East Asian descent.
Understanding the Variant and Its Location
The rs12975333 variant is a genetic marker situated on chromosome 19, specifically in the region upstream of the IFNL3 gene. In genetics, a single nucleotide polymorphism (SNP) represents a variation at a single position in the DNA sequence. While this variant is often discussed in the context of IFNL3, it is important to note that this genomic region is complex. Research has shown that this area also contains the IFNL4 gene, and some studies suggest that the functional impact of variants in this region may be linked to the expression of IFNL4 rather than, or in addition to, IFNL3. Because these genes are located very close together, they are often inherited as a block, making it challenging for researchers to isolate the specific biological mechanism responsible for the observed clinical associations.
The Role of IFNL3 and Interferons
The IFNL3 gene encodes a protein known as interferon lambda 3. Interferons are a group of signaling proteins released by host cells in response to the presence of several pathogens, such as viruses. They act as a critical part of the innate immune system, essentially sounding the alarm to help neighboring cells heighten their antiviral defenses. Historically, this gene was widely referred to in medical literature as IL28B. In 2013, the Human Genome Organization Gene Nomenclature Committee updated the name to IFNL3 to better reflect its biological classification within the interferon lambda family. Understanding this gene is essential for researchers studying how the human immune system recognizes and attempts to eliminate viral infections, particularly chronic infections like hepatitis C, where the body's natural interferon response plays a significant role in determining the outcome of the infection.
Research Associations and Evidence Strength
Numerous genome-wide association studies (GWAS) have identified a strong statistical link between variants in the IFNL3 region and the clearance of hepatitis C virus. Individuals with certain genotypes at this locus have been observed to clear the virus spontaneously more frequently than those with other genotypes. Furthermore, this variant has been studied as a predictor for how patients might respond to interferon-based antiviral therapies. However, the evidence strength for using this SNP as a clinical diagnostic tool is considered limited. Medical policies often classify such testing as experimental or investigational, noting that there is currently insufficient evidence to determine that this genetic information leads to improved net health outcomes for patients. It is important to recognize that while these associations are statistically significant in research cohorts, they do not provide a definitive prediction for an individual's health outcome.
Global Population Frequency
The frequency of the alleles associated with rs12975333 varies significantly across different global populations. Data from large-scale genomic databases indicate that the major allele frequency can range from approximately 0.30 to 0.70 depending on the ancestral background of the population being studied. This wide variation highlights the importance of considering ancestry when interpreting genetic data. Because the distribution of these alleles is not uniform, the prevalence of specific genotypes—and the associated statistical likelihoods for viral clearance—differs between groups. Researchers emphasize that these frequency differences are a normal aspect of human genetic diversity and are critical factors to account for when conducting and interpreting studies on genetic predispositions to infectious diseases.
What This Information Means for You
Genetic information regarding rs12975333 is primarily used in research settings to understand the biological mechanisms of immune response. If you are concerned about hepatitis C or any other viral infection, it is essential to consult with a healthcare professional. This variant should not be used to diagnose a condition or to make personal medical decisions. If you are currently undergoing treatment or considering therapy, discuss all relevant factors, including your medical history and any genetic testing you may have had, with your clinician or pharmacist. They are the only ones qualified to interpret how your specific health profile relates to treatment options. Never change or stop a prescribed medication based on genetic information without direct guidance from your medical provider, as clinical decisions must be based on a comprehensive evaluation of your overall health.
How common is this variant?
The major allele frequency for rs12975333 varies widely, ranging from approximately 0.30 to 0.70 across different global populations.
Frequently asked questions
Is rs12975333 a diagnostic test for hepatitis C?
No, rs12975333 is not a diagnostic test for hepatitis C. It is a genetic marker studied for its statistical association with how the immune system may respond to the virus, but it cannot determine if you have an infection.
Should I get tested for the IFNL3 variant?
Genetic testing for this variant is generally considered experimental for clinical decision-making. You should discuss the necessity of any genetic testing with your doctor, who can determine if it is relevant to your specific medical situation.
Does this variant mean I will definitely clear the virus?
No, genetic associations are based on statistical trends in large populations, not individual certainty. Many factors, including viral load, overall health, and medical treatment, influence whether a person clears a virus.
Can I change my genotype?
No, your genotype is determined at conception and cannot be changed. Genetic information is a tool for understanding your biological predispositions, not a target for modification.
Sources & further reading
Educational information only, last refreshed 9/27/2026. Not medical advice — these associations describe population statistics, not individual predictions.
Curious what your genotype is for rs12975333?
Upload a raw DNA file from 23andMe, AncestryDNA, MyHeritage, or FamilyTreeDNA and see this variant — plus thousands more — interpreted in your full report.
Get my report — $29Related variants in IFNL3
A genetic marker near IFNL3/IFNL4 associated with spontaneous hepatitis C clearance and response to interferon-based therapies, though its predictive power is often secondary to IFNL4 variants like rs368234815.
This variant is a primary predictor of sustained virologic response to interferon-alpha-based therapies in patients with chronic hepatitis C infection.