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Fluorouracil (5-FU) and Capecitabine, a prodrug of 5-FU, are fluoropyrimidine chemotherapy agents used in the treatment of cancer. These drugs form a key component of the chemotherapy regime for colorectal, breast, heapato-pancreato-biliary and many other cancers. These drugs are catabolised by the dihydropyrimadine deyhydrogenase (DPD) enzyme, itself encoded by the DPYD gene. Approximately 3–5% of the European population have a partial DPD enzyme deficiency due to a mutation in the gene (1), and complete enzyme deficiency has also been described. In the US it is reported that up to 8% of the general population have at least a partial deficiency (2). Individuals with a complete deficiency are at risk of life threatening or even fatal chemotherapy toxicity when given 5-FU or Capecitabine. Those with a partial deficiency usually experience gastrointestinal adverse reactions such as prolonged vomiting, as well as haematological effects including a decreased white blood cell count when given therapy at the standard dose. The latter puts patients at risk of serious infection, and a fever is often also reported in those with a partial deficiency. Some studies have shown that almost 25% of patients who are given fluoropyrimidine chemotherapy as a first-line drug experience severe toxicity (3). DPYD testing allows for those with a partial or complete deficiency to be identified, and either a modified dose or alternative therapy given to prevent such adverse reactions. Last month Yourgene Health conducted a mini series of interviews with experts in the field of precision medicine, specifically DPD deficiency.

Dr Gabriel Brooks (GB) is a Medical Oncologist specialising in treating gastrointestinal cancers at Darmouth-Hitchcock Medical Centre. He has a specialist interest in DPD deficiency and cancer care delivery research. 

Holly Ellis (HE) and Hannah Stevens (HS) are both scientists working in Genomics in the NHS. They have both been involved in establishing and running a DPYD testing service at the hospital for routine testing of patients undertaking chemotherapy. Holly is also known on social media as ‘The Scouse Scientist’. In this role she aims to break stereotypes in science, as well as educate and inform the general public on issues such as the use of genomics in precision medicine. 

The 5FU Test Alliance is a patient led organisation founded and run by a small group of people who have either lost a loved one or suffered toxic events themselves as a result of DPD deficiency. Founder member Louise Brown (LB) lost her Father Keith Gadd a month after taking Capecitabine for a successfully removed bowel tumour. They later discovered he had a DPYD mutation.

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