What you carry at this position in your DNA and what research says about it.
Chemotherapy Sensitivity: 9/10 evidence, 25 publications.
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Sample genotype (not yours): A/A
Typical Chemotherapy Response
Normal cytidine deaminase enzyme activity characterizes this genetic profile. It represents the most common variation globally.
What this genotype means: Typical cytidine deaminase enzyme activity; Lower risk of cytarabine-induced liver damage; Typical red blood cell measurements.
Sample genotype (not yours): A/C
Altered Chemotherapy Sensitivity
A single copy of the C allele may alter how the body processes several common chemotherapy medications.
What this genotype means: Moderately reduced cytidine deaminase activity; Increased risk of gemcitabine and cytarabine toxicity; Decreased risk of capecitabine-induced hand-foot syndrome.
Sample genotype (not yours): C/C
Two copies of the C allele are linked to reduced enzyme activity, affecting the metabolism of pyrimidine-based drugs.
What this genotype means: Significantly reduced cytidine deaminase activity; Higher risk of cytarabine and gemcitabine side effects; Lower risk of capecitabine side effects.
Gene function and biological role
Gene Function: The CDA gene encodes cytidine deaminase, an enzyme responsible for the breakdown of cytidine and deoxycytidine into uridine and deoxyuridine [1]. This metabolic pathway is crucial for maintaining the balance of cellular nucleotide pools. Beyond its physiological role, cytidine deaminase is a major player in the metabolism of several pyrimidine-based chemotherapy drugs [2]. It acts as an inactivating enzyme for drugs like gemcitabine and cytarabine, rendering them harmless. Conversely, it serves as an activating enzyme in the multi-step conversion of the prodrug capecitabine into its active, cancer-fighting form [3].
Variant Impact: The rs2072671 variant, also known as p.Lys27Gln or 79A>C, is a missense mutation in the first exon of the CDA gene. This genetic change substitutes the amino acid lysine with glutamine at position 27 of the cytidine deaminase protein. This substitution alters the enzyme's structure and can significantly impact its metabolic rate [4]. Studies indicate that the variant C allele generally leads to reduced cytidine deaminase activity [2]. Consequently, individuals carrying this variant may process certain chemotherapy drugs differently than those with the reference allele [1].
Key Insight: This single genetic variant acts as a double-edged sword, increasing the toxicity of some chemotherapy drugs while simultaneously decreasing the side effects of others.
Location: CDA. Chromosome 1 · 1p36.12 · 20.6 Mb
Estimated prevalence by population
Global 57.3%; European 43.9%; African 82.6%; East Asian 74.0%; South Asian 61.0%; Americas 46.6%; Ashkenazi 31.8%; Finnish 62.5%; Middle Eastern 36.7%; Amish 34.0%.
Estimated AA genotype frequency.
Global 35.1%; European 44.7%; African 16.6%; East Asian 24.1%; South Asian 34.2%; Americas 43.3%; Ashkenazi 49.2%; Finnish 33.1%; Middle Eastern 47.7%; Amish 48.6%.
Estimated AC genotype frequency.
Global 7.6%; European 11.4%; African 0.8%; East Asian 2.0%; South Asian 4.8%; Americas 10.1%; Ashkenazi 19.0%; Finnish 4.4%; Middle Eastern 15.5%; Amish 17.4%.
Estimated CC genotype frequency.
Showing effects for A/A genotype
Pharmacogenomics
Chemotherapy Response
Gemcitabine Toxicity. Evidence: 6/10. Source: PMID 33462346. Lower Nausea Risk.
Capecitabine Response. Evidence: 5/10. Source: PMID 38156857. Poorer Response.
Cytarabine Toxicity. Evidence: 5/10. Source: PMID 19458626. Lower Toxicity Risk.
Cardiovascular & Metabolic
Blood Cell & Iron Traits
Red Blood Cell Size. Evidence: 9/10. Source: PMID 32888494. Typical Size.
Red Blood Cell Count. Evidence: 9/10. Source: PMID 30595370. Slightly Higher.
Lifestyle, Fitness & Aging
Height & Body Size
Height. Evidence: 8/10. Source: PMID 36224396. Typical.
Showing effects for A/C genotype
Gemcitabine Toxicity. Evidence: 6/10. Source: PMID 33462346. Higher Toxicity Risk.
Capecitabine Response. Evidence: 5/10. Source: PMID 38156857. Lower Toxicity Risk.
Cytarabine Toxicity. Evidence: 5/10. Source: PMID 19458626. Higher Toxicity Risk.
Red Blood Cell Size. Evidence: 9/10. Source: PMID 32888494. Slightly Larger.
Red Blood Cell Count. Evidence: 9/10. Source: PMID 30595370. Typical.
Height. Evidence: 8/10. Source: PMID 36224396. Slightly Taller.
Showing effects for C/C genotype
Gemcitabine Toxicity. Evidence: 6/10. Source: PMID 33462346. Higher Nausea Risk.
What this genotype means for the people who carry it
Sample genotype: AA (Homozygous)
Normal cytidine deaminase enzyme function is maintained by this specific genetic profile [1]. When treated with the chemotherapy drug gemcitabine, this genotype is associated with a lower risk of nausea compared to those carrying the C allele [2]. However, some studies suggest a potentially higher risk of overall drug toxicity or neutropenia under specific treatment regimens [3]. For capecitabine therapy, this genotype may be linked to a poorer response rate because the enzyme efficiently processes the drug but might not achieve optimal therapeutic levels in some tumor types [4]. Additionally, cytarabine treatment carries a decreased risk of liver damage for individuals with this profile [5]. In terms of physical traits, this genotype is associated with typical red blood cell size and count [6].
Typical cytidine deaminase enzyme activity; Lower risk of cytarabine-induced liver damage; Typical red blood cell measurements.
Sample genotype: AC (Heterozygous)
A moderate reduction in cytidine deaminase enzyme activity is common with this heterozygous profile [1]. During gemcitabine chemotherapy, this genotype is associated with an increased likelihood of nausea and higher overall drug toxicity [2]. Conversely, when receiving capecitabine, individuals with this genotype show a decreased likelihood of severe drug toxicity and hand-foot syndrome [3]. However, this reduced activation rate might also contribute to a poorer therapeutic response to capecitabine in some cases [4]. For cytarabine therapy, the slower breakdown of the drug can result in increased drug toxicity [5]. Outside of medication response, this genotype is linked to slightly larger red blood cells and a slightly lower red blood cell count [6].
Moderately reduced cytidine deaminase activity; Increased risk of gemcitabine and cytarabine toxicity; Decreased risk of capecitabine-induced hand-foot syndrome.
Sample genotype: CC (Homozygous)
The lowest levels of cytidine deaminase enzyme activity are typically observed with this homozygous variant profile [1]. This slow-metabolizer status means that cytarabine and gemcitabine are broken down much more slowly, which can lead to an increased risk of drug toxicity and nausea [2]. On the other hand, because capecitabine requires cytidine deaminase for activation, this genotype is associated with a decreased risk of capecitabine-induced toxicities, such as hand-foot syndrome [3]. However, this may also lead to a less effective response to capecitabine therapy [4]. In general health traits, this genotype is associated with slightly larger red blood cells, a lower red blood cell count, and a minor increase in height [5] [6].
Significantly reduced cytidine deaminase activity; Higher risk of cytarabine and gemcitabine side effects; Lower risk of capecitabine side effects.
Variants with shared genetic architecture
rs602950 · CDA Gene · Chr 1 · Chemotherapy Toxicity Risk
rs1048977 · CDA Gene · Chr 1 · Chemotherapy Drug Response
rs532545 · CDA Gene · Chr 1 · Chemotherapy Side Effects
Correlation between cytidine deaminase genotype and gemcitabine deamination in blood samples.
The Polygenic and Monogenic Basis of Blood Traits and Diseases.
Identification of new SNPs associated with severe toxicity to capecitabine.
A saturated map of common genetic variants associated with human height.
Content updated August 2026.
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