TSLP rs4795400: What Your Genotype Means
The rs4795400 polymorphism is a non-coding single nucleotide variant located in the promoter region of the TSLP (thymic stromal lymphopoietin) gene. Research links this variant to regulatory changes in cytokine expression that may influence dendritic cell activation and eosinophilic allergic inflammation. Statistical associations identify it as a modest contributor to susceptibility for allergic conditions such as asthma and atopic disease, though its clinical predictive power remains limited.
What each genotype means
Typical TSLP expression
You carry two copies of the common C allele in the TSLP promoter region. In functional and association studies, this genotype is typically associated with standard baseline levels of thymic stromal lymphopoietin expression upon epithelial stimulation. Compared to carriers of the minor T allele, this genotype reflects a standard baseline statistical likelihood for allergic sensitization and childhood-onset asthma, though overall risk is influenced by complex environmental and multi-gene factors.
Carried by approximately 50% to 55% of individuals of European ancestry and is the predominant genotype across most global populations.
Slightly reduced asthma susceptibility
You carry one copy of the protective T allele and one copy of the C allele in the TSLP promoter region. Some association studies suggest that the T allele correlates with slightly altered or attenuated epithelial TSLP induction in response to triggers, conferring a modest protective trend against allergic asthma and eosinophilic airway hyperresponsiveness. Because evidence across diverse populations remains limited and complex, this variant alone does not prevent atopic conditions.
Carried by roughly 35% to 42% of people of European ancestry and is observed at lower frequencies in East Asian populations.
Moderately reduced asthma susceptibility
You carry two copies of the minor T allele in the TSLP promoter region. Published research has linked this homozygous genotype with reduced promoter activity and lower mucosal induction of thymic stromal lymphopoietin, which is associated with a modestly lower statistical risk for asthma and related allergic airway responses. However, evidence remains limited and allergic conditions are multifactorial, meaning lifestyle, environment, and other genetic loci remain critical contributors.
Carried by approximately 7% to 9% of individuals of European ancestry and is relatively uncommon in East Asian and African ancestries.
Genetic Architecture and Variant Location
The single nucleotide polymorphism rs4795400 is positioned within chromosome 5q22.1 in the upstream regulatory promoter region of the TSLP gene. Because it falls within a promoter rather than a protein-coding sequence, rs4795400 does not alter the amino acid sequence of the final protein. Instead, variants in promoter regions typically influence how efficiently transcription factors bind to the DNA, altering the rate of gene transcription. In the human genome, rs4795400 commonly exists as either a cytosine (C) or thymine (T) allele, with C typically serving as the major reference allele and T functioning as the alternative variant allele. Research in functional genomics indicates that promoter variants in the TSLP locus can modulate basal or stimulus-induced expression levels. While rs4795400 is often evaluated as an individual marker, it exists within an extended linkage disequilibrium block on chromosome 5 that encompasses other nearby immune-related loci, meaning its observed effects may reflect cooperative regulatory elements across the region.
Biological Role of the TSLP Gene
The TSLP gene encodes thymic stromal lymphopoietin, an epithelial-derived cytokine structurally and functionally related to interleukin-7. Produced primarily by epithelial cells in the skin, gut, and respiratory tract in response to environmental insults or allergens, TSLP serves as an important upstream master regulator of type 2 (Th2) immune responses. TSLP acts by binding to a heterodimeric receptor complex composed of the TSLP receptor and the interleukin-7 receptor alpha chain (IL-7RA), which is abundantly expressed on myeloid dendritic cells and monocytes. Activation of these dendritic cells prompts them to mature and prime naive T helper cells into Th2 effector cells, which secrete downstream inflammatory cytokines such as IL-4, IL-5, and IL-13. This cascade subsequently drives the recruitment and survival of eosinophils, enhances B-cell immunoglobulin E (IgE) production, and initiates the allergic cascade. Because of its pivotal role in allergic inflammation, the TSLP pathway is also the target of modern biologic therapies designed to suppress severe refractory asthma.
Scientific Evidence and Phenotype Associations
In large-scale genome-wide association studies (GWAS) and candidate gene analyses, the locus containing rs4795400 has been associated with allergic phenotypes, including bronchial asthma, hay fever, elevated eosinophil counts, and atopic sensitization. However, the evidence supporting rs4795400 as a direct causal driver is classified as limited. Across published meta-analyses, common variants at 5q22 typically confer modest odds ratios, often between 1.05 and 1.20, indicating that any single variant explains only a tiny fraction of the total phenotypic variance in allergic disease. Furthermore, association strengths vary depending on the presence of environmental exposures, such as cigarette smoke, microbial contact, and childhood allergen exposure. Many studies have identified significant heterogeneity across different populations and sub-phenotypes, with some associations appearing specific to early-onset atopic asthma rather than non-allergic respiratory disorders. Because asthma and atopy are highly polygenic and heavily influenced by gene-environment interactions, carrying a risk allele at rs4795400 merely shifts population-level statistical susceptibility rather than guaranteeing disease.
Interpreting Results and Clinical Realities
It is crucial to understand what personal genomic data can and cannot reveal regarding rs4795400. Possessing one or two copies of the T allele does not constitute a diagnosis of asthma, eczema, or any allergic condition, nor does having the CC genotype ensure complete immunity from atopy. Unlike high-penetrance Mendelian mutations that directly cause rare monogenic disorders, common polymorphisms identified in GWAS are low-effect trait contributors that operate within an intricate web of hundreds of other genes and environmental triggers. Individuals should not alter, stop, or initiate any medical treatments based on their rs4795400 status. While targeted biologics that inhibit the TSLP pathway exist for patients with severe eosinophilic or allergic asthma, therapeutic decisions are made entirely on clinical criteria, biomarker evaluations, and specialist assessment, not personal genotypes at this SNP. Anyone experiencing respiratory symptoms or chronic allergies should seek guidance from a qualified physician or allergist.
How common is this variant?
The minor allele frequency for rs4795400 is approximately 0.28 (28%) in populations of European ancestry, meaning the variant allele is widespread. Allele and genotype frequencies fluctuate across global populations, with varied prevalence documented in East Asian, African, and admixed cohorts.
Frequently asked questions
What is rs4795400?
The rs4795400 polymorphism is a naturally occurring single nucleotide variation located in the promoter region of the human TSLP gene on chromosome 5. It does not disrupt the protein's coding sequence but is studied for its potential effects on the level of TSLP cytokine production.
Does having the rs4795400 variant mean I will get asthma?
No. The rs4795400 variant is merely a common genetic marker with a minor statistical association with allergic traits in population studies. Many individuals carrying the variant never develop asthma or allergies, as these conditions depend on hundreds of genes alongside environmental exposures.
Can rs4795400 be used to select asthma medication?
Currently, clinical guidelines do not use rs4795400 to select asthma medications or biologics. Although drugs targeting TSLP exist, their prescription is guided by clinical severity, symptom history, and standard lab markers rather than your personal genotype at this locus.
How does TSLP influence the immune system?
TSLP functions as an upstream cytokine released by epithelial barriers when exposed to allergens, pathogens, or irritants. It primes dendritic cells to activate type 2 helper T cells, which promote eosinophil survival, IgE production, and allergic airway inflammation.
Sources & further reading
Educational information only, last refreshed 9/10/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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