Fluoropyrimidine (5-FU) toxicity risk

DPYD breaks down the chemotherapy drugs 5-fluorouracil and capecitabine. A no-function variant lets these drugs accumulate to dangerous levels, risking severe toxicity.

Possible results

Normal 5-FU breakdown. You don't carry the no-function DPYD variant, so the enzyme that breaks down the chemotherapy drugs 5-fluorouracil and capecitabine works normally as far as this gene goes. These drugs should clear at the usual rate (other DPYD variants aren't covered here).

Higher 5-FU toxicity risk. You carry one non-working copy of DPYD, so you break down the chemo drugs 5-fluorouracil and capecitabine more slowly. If you ever need these specific chemotherapies, this genotype is important, since a reduced dose is usually recommended to avoid severe side effects. It only matters in that context.

High 5-FU toxicity risk. You have two non-working copies of DPYD and make little or none of the enzyme that clears 5-fluorouracil and capecitabine. These chemo drugs could reach dangerous levels, so they're generally avoided or used only with major dose changes. This is critical information if cancer treatment ever comes up.

Evidence & sources

Across global populations, fewer than 1% of people carry two copies of this variant, and about 99% carry none.

CPIC provides dosing guidance for fluorouracil based on this gene.

This variant appears in 1 published genetic study: PubMed 35347128.

Related

CYP2C19 metabolizer status (clopidogrel & others) · Drug acetylation speed (NAT2) · Efavirenz / drug metabolism (CYP2B6*6) · Gilbert syndrome (UGT1A1 gene) · Hepatitis C treatment response (IL28B) · Opioid receptor response (OPRM1 A118G) · Tacrolimus metabolism (CYP3A5 gene)