DPYD and dihydropyrimidine dehydrogenase deficiency: People found to carry DPYD variants (c.1905 + 1G > A, (DPYD *2A), c.2846A > T, c.1679 T > G and c.1236G > A/HapB3), have decreased function of their alleles to make DPD enzyme, resulting in DPD deficiency and FP toxicity when standard FP doses are administered [17, 18] (Table 1).