DPYD*2A (rs3918290) DPYD*13 (rs55886062), c.2846A>T (rs67376798, D949V) and c.1236G>A-HapB3 (rs56038477), the genetic variants included in the international pharmacogenetic guidelines for drug adjustments do not cover all the cases of DPD deficiency and their screening could not predict with sufficient sensitivity the risk of early severe toxic events induced by FPs. Here, DPYD is linked to dihydropyrimidine dehydrogenase deficiency.