5-Fluorouracil (5-FU) are fluoropyrimidine-based chemotherapeutic agents that are widely used for the treatment of colorectal cancer and other solid tumors. The dihydropyrimidine dehydrogenase (DPYD) gene encodes the rate-limiting enzyme for 5-FU catabolism and eliminates over 80% of administered 5-FU. Mutations in DPYD gene can result in a wide variability of dihydropyrimidine dehydrogenase (DPD) enzymatic activity, ranging from partial (3%-5% of population) to complete loss (0.2% of population) of function. Patients who are deficient in DPD are at an increased risk for side effects and toxicity when undergoing 5-FU treatment. DPD deficiency shows large phenotypic variability, ranging from no symptoms to a convulsive disorder with motor and intellectual disabilities.

The key DPYD mutations associated with reduced enzymatic activity are c.1905+1 G>A, c.1679 T>G, c.2846 A>T & 1129-5923C>G. The following table displays the DPYD variants detected by this assay, the corresponding star allele, and the effect on DPYD enzyme