Initial dose reduction of at least 50% is proposed for patients heterozygous for DPYD*2A, DPYD*13 and c.2846A > T, who are considered to have intermediate or partial DPD enzyme activity, while a choice of alternative drug is strongly recommended for patients with complete DPD deficiency [23]. The gene discussed is DPYD; the disease is dihydropyrimidine dehydrogenase deficiency.