IL18 rs187238: Understanding the -137G/C Promoter Variant
The rs187238 variant is a single nucleotide polymorphism located in the promoter region of the IL18 gene. It is associated with variations in the transcriptional activity of the gene and the resulting circulating levels of the pro-inflammatory cytokine IL-18.
What each genotype means
Typical IL-18 promoter activity
You carry two copies of the common G allele, historically designated as -137G in scientific literature. In functional assays, this genotype is linked to typical promoter transcription and baseline circulating interleukin-18 cytokine levels. Published association studies have linked the GG genotype with modest differences in inflammatory and cardiovascular disease susceptibility, although overall clinical evidence remains limited and variable across diverse populations.
Carried by approximately 45% to 55% of individuals of European ancestry and is the predominant genotype across most global populations.
Moderately altered IL-18 expression
You carry one copy of the -137C minor allele and one copy of the -137G allele. Laboratory studies indicate that the C allele alters nuclear factor binding, which may lead to slightly lower promoter activity and modestly reduced circulating IL-18 levels relative to the GG genotype. While candidate gene studies report subtle shifts in inflammatory and autoimmune traits, these associations are weak and findings vary across ancestry groups.
Carried by roughly 35% to 45% of European populations and occurs at lower frequencies in East Asian cohorts.
Reduced IL-18 promoter activity
You carry two copies of the minor C allele (often noted as -137C/C in published literature). This genotype is experimentally associated with lower promoter transcriptional activity and reduced baseline production of the pro-inflammatory cytokine interleukin-18. Clinical association studies suggest possible attenuation of certain inflammation-related risks, though the overall strength of evidence is limited and should not be considered diagnostic or predictive.
Carried by approximately 5% to 10% of individuals of European ancestry and is relatively uncommon worldwide.
What is the rs187238 Variant?
The rs187238 variant, often referred to as the -137G/C polymorphism, is a specific change in the DNA sequence within the promoter region of the IL18 gene. A promoter is a segment of DNA that acts as an on-off switch for a gene, determining how much of a protein is produced. In this case, the substitution of a guanine (G) for a cytosine (C) at position -137 can alter the binding affinity of transcription factors, which are proteins that help initiate the process of gene expression. Because this variant sits in a regulatory area, it is considered a functional SNP, meaning it has the potential to influence the biological output of the gene rather than just changing the structure of the protein itself.
The Role of the IL18 Gene
The IL18 gene provides instructions for making interleukin-18, a potent pro-inflammatory cytokine. Cytokines are signaling molecules that play a critical role in the immune system, helping to coordinate the body's response to infection and inflammation. IL-18 is particularly known for its ability to induce the production of interferon-gamma and promote the activity of T-helper 1 cells and cytotoxic T-lymphocytes. By regulating these immune pathways, IL-18 helps the body defend against pathogens. However, because it is a strong driver of inflammation, the levels of IL-18 must be tightly controlled. When this regulation is disrupted, it can contribute to chronic inflammatory states, which is why researchers study promoter variants like rs187238 to understand how genetic differences might influence individual immune responses.
Research and Associations
Research into rs187238 has explored its potential link to various inflammatory and autoimmune conditions, including rheumatoid arthritis, systemic lupus erythematosus, and cardiovascular health. Some studies suggest that the G allele may facilitate higher levels of IL-18 mRNA expression compared to the C allele, which has been associated with diminished promoter activity. However, the evidence remains limited and often conflicting across different populations. For instance, while some studies have found associations between this variant and disease severity in specific cohorts, others have found no statistically significant difference in genotype frequencies between patient groups and healthy controls. These mixed results highlight that genetic associations are rarely straightforward and are often influenced by a person's broader genetic background, environmental factors, and the specific disease context being studied.
Population Frequency
The frequency of the rs187238 variant varies across different ancestral groups. In European populations, the minor allele (C) is typically observed at a frequency of approximately 25% to 35%. Because this is a common variant, a significant portion of the population carries at least one copy of the C allele, making it a frequent subject of study in genetic epidemiology.
Interpreting Your Genetic Information
It is important to understand that having a specific genotype for rs187238 does not mean you will develop any particular health condition. Genetic variants are only one piece of a very complex puzzle that includes lifestyle, environment, and other genetic factors. Because the evidence linking this SNP to specific health outcomes is limited and often inconsistent, it is not currently used as a diagnostic tool in clinical practice. If you have questions about your health or how your genetics might influence your risk for inflammatory conditions, the best course of action is to consult with a qualified healthcare provider. They can help you interpret your health history in the context of your overall well-being and provide guidance based on established clinical standards rather than individual genetic markers.
How common is this variant?
The minor allele (C) has a frequency of approximately 25-35% in European populations, making the C/C and G/C genotypes relatively common.
Frequently asked questions
Is rs187238 a diagnostic test for inflammation?
No, rs187238 is not a diagnostic test. It is a genetic variant studied in research settings to understand how immune responses might differ between individuals, but it cannot predict or diagnose inflammatory diseases.
Does the C allele cause disease?
No, the C allele does not cause disease. While some research explores its association with certain conditions, genetic variants are only one of many factors that contribute to health and disease risk.
Should I change my diet based on my IL18 genotype?
There is no evidence-based dietary recommendation linked to the rs187238 genotype. You should discuss any significant changes to your diet or health plan with a doctor or registered dietitian.
Why do studies show different results for this SNP?
Genetic studies often show different results because of variations in study design, the size of the groups studied, and the diverse genetic and environmental backgrounds of the participants in different populations.
Sources & further reading
Educational information only, last refreshed 10/11/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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