DPYD rs3957357: Fluoropyrimidine Toxicity Risk
The rs3957357 variant is a single-nucleotide polymorphism located in an intronic region of the DPYD gene. It has been investigated for its potential role in modulating the expression of dihydropyrimidine dehydrogenase (DPD), the key enzyme responsible for clearing fluoropyrimidine chemotherapy drugs. Certain studies associate this variant with altered drug metabolism and an elevated risk of severe treatment-related toxicities, though overall clinical evidence remains limited.
What each genotype means
| Genotype | What the research suggests | Reading |
|---|---|---|
| GG | Carries two copies of the common G allele. This genotype represents the standard baseline sequence in most studied reference cohorts and is not associated with an altered risk profile at this specific locus. | Informational |
| AG | Carries one copy of the minor A allele and one reference G allele. Some research suggests heterozygous individuals may exhibit modest changes in DPYD expression, but clinical evidence regarding chemotherapy toxicity risk remains limited. | Higher attention |
| AA | Carries two copies of the minor A allele. Homozygosity for this regulatory variant has been evaluated in cohort studies for elevated risk of fluoropyrimidine-related toxicities, though data across clinical trials are inconclusive. | Higher attention |
Genomic Location and Variant Characteristics
The single-nucleotide polymorphism rs3957357 is situated within an intronic region of the DPYD gene on chromosome 1. As an intronic variant, it does not alter the amino acid sequence of the resulting protein directly. Instead, research indicates it may act as a regulatory variant, potentially influencing transcription factor binding, pre-mRNA processing, or overall gene expression levels. In genetic databases like dbSNP and PharmGKB, the variant is typically documented with an adenine (A) or guanine (G) allele. Because non-coding intronic variants often exert subtle or context-dependent regulatory effects, their mechanistic impacts are frequently more complex to characterize than classic coding loss-of-function mutations.
The Biological Role of DPYD and Drug Clearance
The DPYD gene provides instructions for producing dihydropyrimidine dehydrogenase, an essential enzyme responsible for breaking down the pyrimidine bases uracil and thymine. In oncology, DPD plays a critical role in pharmacokinetics: it eliminates more than 80% of administered fluoropyrimidine chemotherapies, including 5-fluorouracil (5-FU) and its oral prodrug capecitabine. When DPD enzyme activity is significantly impaired, these cytotoxic drugs accumulate to dangerous concentrations in systemic circulation. This accumulation can lead to life-threatening adverse reactions, such as severe neutropenia, profuse diarrhea, mucositis, and neurotoxicity. Consequently, genetic variation across the DPYD locus is heavily studied to predict fluoropyrimidine safety.
Evidence Strength and Clinical Guidelines
While primary clinical guidelines from consortia like the Clinical Pharmacogenetics Implementation Consortium (CPIC) focus heavily on established, high-impact variants such as DPYD*2A (rs3918290) and c.2846A>T (rs67376798), evidence for rs3957357 remains classified as limited. Several pharmacogenetic association studies have observed that carriers of the minor allele exhibit higher rates of grade 3 or higher toxicities during 5-FU or capecitabine regimens. However, findings across independent cohorts have been mixed, and rs3957357 is not currently utilized as a standalone actionable marker in standard consensus dosing algorithms. Its precise predictive power remains an active subject of ongoing pharmacogenomic research.
Population Distribution and Ancestry Patterns
Population genetics datasets, including gnomAD and the 1000 Genomes Project, show that rs3957357 is relatively common in several global groups. The minor allele frequency typically ranges between 15% and 25% across individuals of European and American ancestries. In contrast, its distribution can vary substantially in African, East Asian, and South Asian populations. Because common intronic polymorphisms frequently differ in frequency across geographic groups, evaluating background ancestry and potential linkage disequilibrium with other functional loci is essential when interpreting cohort-level pharmacogenomic associations.
Interpreting Results and Clinical Perspective
Discovering an rs3957357 genotype on a personal genomic report does not constitute a clinical diagnosis of complete DPD deficiency, nor does it guarantee an adverse drug reaction. Chemotherapy tolerance depends on multiple factors, including renal and liver function, co-administered medications, patient performance status, and other well-validated DPYD alleles. Individuals scheduled to undergo treatment with 5-fluorouracil, capecitabine, or tegafur should never adjust or refuse treatment on their own based on recreational or direct-to-consumer data. Any questions about pharmacogenetic susceptibility and pre-treatment screening should be discussed directly with an oncologist or clinical pharmacologist.
How common is this variant?
The minor allele frequency of rs3957357 typically ranges from approximately 0.15 to 0.25 in European and American populations, while frequencies vary across other global ancestral groups.
Frequently asked questions
What is DPYD rs3957357?
The rs3957357 polymorphism is an intronic single-nucleotide variant in the DPYD gene. It has been researched for potential regulatory effects on dihydropyrimidine dehydrogenase levels and fluoropyrimidine chemotherapy tolerance.
Does having rs3957357 mean I cannot take capecitabine or 5-FU?
No, carrying this variant does not mean you cannot receive these medications. Evidence connecting rs3957357 to severe drug toxicity is considered limited, and major clinical guidelines rely on other core DPYD variants to guide prescribing.
How is rs3957357 different from DPYD*2A?
DPYD*2A is a well-established splice-site mutation that severely disrupts enzyme function and mandates dose reduction or drug avoidance under CPIC guidelines. In contrast, rs3957357 is an intronic variant with modest, less conclusive evidence regarding its clinical impact.
Should I change my chemotherapy dose if I carry this variant?
You should never alter or stop any medical treatment based on individual genetic test results. Always review pharmacogenetic findings with your oncologist or hospital pharmacist to determine if specialized DPD activity testing or dose adjustments are warranted.
Sources & further reading
Educational information only, last refreshed 9/9/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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