UGT1A1 and dihydropyrimidine dehydrogenase deficiency: Moreover, patients with dihydropyrimidine dehydrogenase (DPD) deficiency (present in 8% of African-American and 3–5% of Caucasian patients) [30] are at increased risk of toxicity when treated with fluoropyrimidines while those with uridine diphosphate glucoronosyltransferase 1A (UGT1A) polymorphisms (present in at least 20% of Caucasians and 15% of African-Americans or Asian patients) [31] are at an increased risk of toxicity when treated with irinotecan.