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DPYS gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

DPYS gene

The DPYS gene provides instructions for making the dihydropyrimidinase enzyme, which is essential for breaking down pyrimidines and certain cancer-treating drugs.

Normal Function

The DPYS gene provides instructions for making an enzyme called dihydropyrimidinase. This enzyme is involved in the breakdown of molecules called pyrimidines, which are building blocks of DNA and its chemical cousin RNA. The dihydropyrimidinase enzyme is involved in the second step of the three-step process that breaks down pyrimidines. This step opens the ring-like structures of molecules called 5,6-dihydrothymine and 5,6-dihydrouracil.

Further breakdown of these molecules leads to the production of other molecules called beta-aminoisobutyric acid and beta-alanine, which are thought to play roles in the nervous system. Beta-aminoisobutyric acid increases the production and release of a protein called leptin, which has been found to help protect brain cells from damage caused by toxins, inflammation, and other factors. Beta-alanine is thought to be involved in sending signals between nerve cells (synaptic transmission) and in controlling the level of a chemical messenger (neurotransmitter) called dopamine.

The dihydropyrimidinase enzyme also helps break down certain drugs called fluoropyrimidines that are used to treat cancer. Common examples of these drugs are 5-fluorouracil and capecitabine.

Health Conditions Related to Genetic Changes

Dihydropyrimidinase deficiency

At least 23 DPYS gene mutations have been identified in people with dihydropyrimidinase deficiency, a disorder that can cause neurological and gastrointestinal problems in some affected individuals. Other people with dihydropyrimidinase deficiency have no signs or symptoms related to the disorder, and in these individuals the condition can be diagnosed only by laboratory testing.

People with dihydropyrimidinase deficiency, including those who otherwise exhibit no symptoms, may be vulnerable to severe, potentially life-threatening toxic reactions to fluoropyrimidines. These drugs may not be broken down efficiently and can build up to toxic levels in the body (fluoropyrimidine toxicity), leading to drug reactions including gastrointestinal problems, blood abnormalities, and other signs and symptoms.

The DPYS gene mutations that cause dihydropyrimidinase deficiency greatly reduce or eliminate dihydropyrimidinase enzyme function. As a result, the enzyme is unable to begin the breakdown of 5,6-dihydrothymine and 5,6-dihydrouracil. Excessive amounts of these molecules accumulate in the blood and in the fluid that surrounds and protects the brain and spinal cord (the cerebrospinal fluid or CSF) and are released in the urine.

Failure to complete this step in the breakdown of pyrimidines also impedes the final step of the process, which produces beta-aminoisobutyric acid and beta-alanine. Reduced production of these molecules may impair their function in the nervous system, leading to neurological problems in some people with dihydropyrimidinase deficiency. It is unknown why some people with dihydropyrimidinase deficiency do not develop health problems related to the condition; other genetic and environmental factors likely help determine the effects of this disorder.

Other Names for This Gene

  • DHP
  • DHPase
  • dihydropyrimidine amidohydrolase
  • hydantoinase

Frequently Asked Questions

The dihydropyrimidinase enzyme is responsible for producing beta-alanine and beta-aminoisobutyric acid, which play roles in nervous system function. Beta-alanine is involved in synaptic transmission and dopamine regulation, while beta-aminoisobutyric acid helps protect brain cells from toxin and inflammation damage. Deficiencies in these molecules may contribute to the neurological problems seen in some patients with dihydropyrimidinase deficiency, although the exact mechanism of how low levels cause specific symptoms is still an area of ongoing research.
Yes, many individuals with DPYS mutations have no visible neurological or gastrointestinal symptoms and may only be identified through specific laboratory testing. Diagnosis in asymptomatic individuals is typically confirmed by measuring enzyme activity in red blood cells or through genetic testing that identifies specific mutations in the DPYS gene. This is particularly important to determine before initiating cancer treatment to prevent severe drug reactions.
Patients with dihydropyrimidinase deficiency often experience severe, life-threatening toxicity when treated with fluoropyrimidine chemotherapy drugs because their bodies cannot break down these medications efficiently. This leads to dangerously high levels of the drug in the bloodstream, causing severe side effects such as intense diarrhea, vomiting, mouth sores, and bone marrow suppression. Clinicians must be aware of this genetic status before prescribing these drugs, as standard doses can be fatal for individuals with this deficiency.
Dihydropyrimidinase deficiency is typically inherited in an autosomal recessive pattern, meaning a person must inherit two mutated copies of the DPYS gene, one from each parent, to have the condition. If an individual is diagnosed with the deficiency, their siblings and potentially their parents should be considered for genetic counseling and testing, as they may carry the mutation or be affected. Identifying carriers is crucial for family planning and for ensuring safe medical care if any family member requires fluoropyrimidine-based chemotherapy.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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