Your body uses the DPYD gene to make an enzyme that breaks down natural building blocks of DNA and cancer medicines such as 5-fluorouracil and capecitabine. If this gene works poorly, those drugs can stay in the body too long and cause major side effects, and rare inherited loss of function can also affect brain development. Some people first learn about this gene when treatment is being checked before these medicines are used. Knowing your DPYD result can help explain why drug safety differs from one person to another.
What is a gene?
Genes are stretches of DNA that hold instructions your cells use to make molecules or regulate processes throughout the body. Some genes provide the directions for producing proteins, the working parts of cells. Other genes mostly help direct when certain processes happen, where they happen, and how active they are. Taken together, genes affect how the body develops and functions, and they can influence how you respond to food, stress, or medications. For a deeper look at this topic, you can learn more in the LearnHub.
Overview
DPYDGene function
What if the gene works
The DPYD gene helps your body break down pyrimidines, the building blocks of DNA and RNA. It also clears fluoropyrimidine medicines and supports normal chemical balance in cells.
Risk
What if the gene does not work
Variants in the DPYD gene can slow breakdown of fluoropyrimidine medicines, increasing the risk of severe side effects. Milder variants may have smaller effects, while more severe variants can also cause rare DPD deficiency with developmental and neurologic features.
Treatment
What does that mean for your treatment
Pathogenic or loss-of-function variants in the DPYD gene can greatly reduce breakdown of fluoropyrimidine medicines such as fluorouracil, capecitabine, and tegafur. This is well established and can change treatment: many people need a much lower starting dose, and some should avoid these drugs and use alternatives.
Conditions associated with DPYD
Gene function
What if the gene works
Your body constantly makes, uses, and clears small natural chemicals that help build DNA and RNA. The DPYD gene helps with this cleanup by starting the breakdown of uracil and thymine, two closely related building blocks. This supports steady chemical balance in many tissues, especially the liver.
One of the main jobs of the DPYD gene is to start breaking down uracil after your cells have used it. This helps your body manage normal cell turnover and keeps natural chemical levels more balanced.
It also helps process thymine, a related building block used in DNA. By beginning this step, the DPYD gene supports the body’s usual recycling and cleanup work.
Through its protein, the DPYD gene helps control how quickly certain pyrimidines (building blocks related to DNA and RNA) are cleared. This is a key part of what the DPYD gene does in the body each day.
What is a variant?
A genetic variant is a small difference in the DNA sequence of a gene. These changes are common and help explain normal human diversity, such as differences in appearance, metabolism, or the body’s response to environmental influences. Many variants do not have any noticeable effect and simply represent natural genetic variation. In some situations, though, a variant can change a gene’s function to a greater extent and may contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
DPYD gene variants can change how much working DPD enzyme a cell makes, or how well the enzyme folds and breaks down fluoropyrimidine drugs such as 5-fluorouracil and capecitabine. Some DPYD gene variants cause only partial loss of activity, while more severe variants leave little or no activity. This functional range helps explain why some people process these medicines a bit more slowly, while others can have much stronger drug effects.
How variants are linked to conditions
Pathogenic variants in the DPYD gene can cause dihydropyrimidine dehydrogenase deficiency, a rare inherited condition linked to developmental delay, seizures, and other neurologic features in some people. More often, reduced-function changes are identified in the setting of DPYD gene variants and fluoropyrimidine toxicity, because they are strongly associated with a higher risk of severe side effects from 5-fluorouracil, capecitabine, and related chemotherapy. These drug-response variants affect risk, not certainty, and people can differ in how strongly they are affected.
A variant is not necessarily a diagnosis
Variants in genes are a routine part of human biology and are widely seen in the general population. Most do not have a direct effect on health and simply reflect normal human diversity. For many genes, having a variant linked to a condition suggests a possible association rather than a definite diagnosis, especially when several genes and environmental factors play a role. In some situations, though, a single well-characterized variant in a specific gene can be enough to confirm a diagnosis.
Are there things that can increase or change my risk?
For DPYD, risk mainly changes if you are treated with certain chemotherapy medicines, especially fluorouracil or capecitabine. The exact DPYD variant matters, and risk is usually higher with two changed copies than with one. Dose, age, and kidney or liver problems can also raise the chance of serious side effects.
Inheritance of DPYD variants
For DPD deficiency, variants in the DPYD gene are inherited in an autosomal recessive pattern. This means a child usually inherits one altered copy of the DPYD gene from each parent. When both parents carry one variant, each pregnancy has a 25% chance of a child with the condition, a 50% chance of a child who is a carrier, and a 25% chance of a child with two usual copies. In discussions of DPYD gene inheritance, it also helps to know that carriers can still pass the variant to sons or daughters because the DPYD gene is on an autosome, not a sex chromosome.
What does my DPYD result mean for my family?
For families, a DPYD result can matter because close relatives may also carry the same change. In families affected by full DPD deficiency, brothers, sisters, and future children may be more likely to carry a DPYD change, and some relatives may have the condition themselves. A parent, child, or sibling who shares the variant may also have a higher chance of severe side effects from certain chemotherapy drugs.
Genetic information
Genetic testing
How you find out about variants
DPYD genetic testing before capecitabine or 5-fluorouracil looks for inherited variants in a blood sample or cheek swab. A laboratory reads the DPYD gene and checks for well-established changes linked to slower drug breakdown. Results can show whether you carry a variant that may affect drug safety.
When should I consider getting a genetic test?
DPYD testing is worth considering before starting chemotherapy with fluorouracil (5-FU), capecitabine, or related medicines, because some inherited changes can make these drugs build up and cause serious side effects. It can also help explain unusually severe reactions after a first dose or a family history of major problems with these treatments.
A genetic result is only one part of your health story
A genetic result can be informative, but how much it explains depends on the condition and on the type of variant involved. Many factors also shape how the body works over time, including lifestyle, environment, age, and medical history. For some conditions, especially those influenced by many genes, genetic information provides context rather than certainty and is best understood together with other parts of care. In other situations, a genetic result can offer a clear answer. In areas such as medication response, genetic results can also help put individual experiences into context.
Pharmacogenetics
How variants shape your response to medicine
Variants in the DPYD gene can change how your body breaks down certain chemotherapy medicines, especially fluoropyrimidines such as 5-fluorouracil and capecitabine. If you carry a reduced function DPYD variant, these medicines may build up in the body, which can raise the chance of stronger side effects. This is one example of pharmacogenetics: common genetic differences help explain why the same medicine can work differently or feel harder to tolerate from one person to another.
What is Pharmacogenetics?
Pharmacogenetics examines how differences in a person’s genes affect the way medications work. By looking at relationships between genes and drugs, it helps explain why the same treatment can have different effects in different people. With many medicines, genes influence either how much effect a drug has or how the body handles it. This information can support treatment choices that are more informed and more tailored to the individual. More detailed information on this topic is available in the LearnHub.
Drugs influenced by the DPYD gene
When should I seek medical advice?
If you are about to start certain chemotherapy medicines from the fluoropyrimidine family, it is worth talking with your doctor about the DPYD gene before treatment begins. Some people with DPYD changes break down these medicines more slowly and can have severe side effects, so this discussion also matters if side effects appear soon after starting treatment.
History
The DPYD gene entered medical practice through studies of unexpected, sometimes life threatening reactions to 5-fluorouracil and related chemotherapy drugs. In the 1980s and 1990s, researchers connected these reactions to reduced activity of the body system that breaks down these medicines, and later traced part of that risk to variants in the DPYD gene. Initially understood only through visible traits, later recognized as tied to a specific gene, this work helped shift cancer care toward pharmacogenetics, the use of genes to guide drug treatment. Over time, descriptions became more precise. Specific DPYD variants were added to clinical guidance, and testing before treatment became part of routine care in several countries. Today, DPYD is widely recognized as a landmark gene in safer chemotherapy prescribing.