What you carry at this position in your DNA and what research says about it.
Chemotherapy Toxicity: 6/10 evidence, 43 publications.
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Sample genotype (not yours): T/T
Typical Chemotherapy Toxicity Risk
Standard processing of fluoropyrimidine-based chemotherapy drugs is typical for this genetic profile. It does not elevate the risk of severe side effects or toxicity from these medications.
What this genotype means: Standard chemotherapy drug clearance; Typical baseline risk of side effects.
Sample genotype (not yours): C/C
Higher Risk of Chemotherapy Toxicity
Reduced microRNA expression and an increased risk of severe chemotherapy side effects are characteristic of this profile. It is also associated with slightly higher white blood cell counts.
What this genotype means: Increased risk of severe chemotherapy side effects; Slightly higher baseline white blood cell counts.
Sample genotype (not yours): T/C
An increased risk of severe side effects from fluoropyrimidine chemotherapies is linked to this genetic profile.
What this genotype means: Increased risk of severe chemotherapy side effects; Higher likelihood of treatment-induced neutropenia.
Gene function and biological role
Gene Function: The MIR27A gene encodes microRNA-27a, a small non-coding RNA molecule that plays a key role in post-transcriptional gene regulation. It regulates the expression of various target genes involved in cell proliferation, apoptosis, and drug metabolism. Notably, microRNA-27a acts as a direct regulator of dihydropyrimidine dehydrogenase, an enzyme critical for breaking down fluoropyrimidine chemotherapy drugs [1]. Variations in this gene can alter microRNA expression levels, thereby influencing enzyme activity and drug sensitivity [2]. This regulatory network is crucial for determining how patients tolerate specific cancer therapies.
Variant Impact: The rs895819 variant is a single nucleotide polymorphism located in the stem-loop region of the pre-microRNA-27a sequence. This genetic change from a thymine to a cytosine allele can alter the secondary hairpin structure of the pre-microRNA [1]. Such structural changes can affect the processing and maturation of the microRNA by cellular machinery. Consequently, this variant leads to altered levels of mature microRNA-27a, which in turn impacts the regulation of target genes [2]. These downstream effects are particularly significant for chemotherapy metabolism and certain cell-type counts.
Key Insight: Carrying the C allele can significantly reduce the expression of mature microRNA-27a in plasma, which unexpectedly increases the risk of severe toxicity when undergoing standard chemotherapy with fluoropyrimidines.
Location: MIR27A. Chromosome 19 · 19p13.12 · 13.8 Mb
Estimated prevalence by population
Global 39.8%; European 45.2%; African 25.5%; East Asian 50.9%; South Asian 45.2%; Americas 45.1%; Ashkenazi 51.8%; Finnish 39.7%; Middle Eastern 48.8%; Amish 61.6%.
Estimated TT genotype frequency.
Global 45.6%; European 44.1%; African 50.0%; East Asian 40.9%; South Asian 44.0%; Americas 44.1%; Ashkenazi 40.3%; Finnish 46.6%; Middle Eastern 42.1%; Amish 33.8%.
Estimated TC genotype frequency.
Global 14.6%; European 10.7%; African 24.5%; East Asian 8.2%; South Asian 10.7%; Americas 10.8%; Ashkenazi 7.9%; Finnish 13.7%; Middle Eastern 9.1%; Amish 4.6%.
Estimated CC genotype frequency.
Showing effects for T/T genotype
Pharmacogenomics
Chemotherapy Response
Chemotherapy Toxicity. Evidence: 6/10. Source: PMID 38353109. Typical Risk.
Cardiovascular & Metabolic
Blood Cell & Iron Traits
Lymphocyte Count. Evidence: 8/10. Source: PMID 32888494. Typical.
Myeloid White Cell Count. Evidence: 6/10. Source: PMID 32888493. Typical.
Cancer & Oncology
Colorectal Cancer
Colorectal Cancer. Evidence: 4/10. Source: PMID 30447914. Typical Risk.
Showing effects for C/C genotype
Chemotherapy Toxicity. Evidence: 6/10. Source: PMID 38353109. Increased Risk.
Lymphocyte Count. Evidence: 8/10. Source: PMID 32888494. Higher.
Myeloid White Cell Count. Evidence: 6/10. Source: PMID 32888493. Higher.
Colorectal Cancer. Evidence: 4/10. Source: PMID 30447914. Increased Risk.
Showing effects for T/C genotype
Lymphocyte Count. Evidence: 8/10. Source: PMID 32888494. Slightly Higher.
Myeloid White Cell Count. Evidence: 6/10. Source: PMID 32888493. Slightly Higher.
Colorectal Cancer. Evidence: 4/10. Source: PMID 30447914. Slightly Increased.
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
A genetic profile with two copies of the common major allele is typical for this group. This genetic profile is associated with typical levels of microRNA-27a expression, which supports normal regulation of the dihydropyrimidine dehydrogenase enzyme. Consequently, when treated with fluoropyrimidine-based chemotherapies like 5-fluorouracil or capecitabine, standard drug clearance is expected [1]. There is no genetically elevated risk of severe toxicities, such as profound neutropenia or gastrointestinal distress, that is seen in carriers of the variant allele [2]. This genotype represents the baseline risk profile in the general population. Most individuals in this category tolerate standard chemotherapy regimens without genetic complications.
Standard chemotherapy drug clearance; Typical baseline risk of side effects.
Sample genotype: CC (Homozygous)
A homozygous profile with two copies of the minor variant allele has been shown to severely reduce the circulating levels of mature microRNA-27a in plasma [1]. This reduction in microRNA expression can disrupt the normal regulation of metabolic enzymes, leading to an increased risk of severe toxicity when treated with fluoropyrimidine-based chemotherapies [2]. Common adverse reactions associated with this genotype include severe neutropenia and gastrointestinal distress [3]. Additionally, large-scale genetic studies have linked this genotype to slightly higher baseline counts of lymphocytes and myeloid leukocytes, though these usually remain within normal ranges [4]. Personalized medicine aims to minimize side effects while maximizing therapeutic efficacy.
Increased risk of severe chemotherapy side effects; Slightly higher baseline white blood cell counts.
Sample genotype: TC (Heterozygous)
Altered microRNA-27a expression is associated with this heterozygous profile, which can impair the regulation of dihydropyrimidine dehydrogenase, the primary enzyme responsible for metabolizing fluoropyrimidine drugs. Clinical studies have shown that a heterozygous profile leads to a significantly higher likelihood of experiencing severe chemotherapy-induced toxicities [1]. These adverse effects frequently include severe neutropenia, which is a dangerous drop in white blood cell counts, as well as intense gastrointestinal complications [2]. The variant serves as an important independent risk factor for treatment safety. Patients undergoing cancer therapies often receive multiple medications, making drug-gene interactions highly relevant.
Increased risk of severe chemotherapy side effects; Higher likelihood of treatment-induced neutropenia.
Variants with shared genetic architecture
rs75017182 · DPYD Gene · Chr 1 · Chemotherapy Drug Toxicity
rs17376848 · DPYD Gene · Chr 1 · Chemotherapy Toxicity Risk
rs2297595 · DPYD Gene · Chr 1 · Chemotherapy Toxicity Risk
Content updated September 2026.
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