DPYD and hyperinsulinemic hypoglycemia, familial, 4: For example, patients with deletion polymorphism of the thymidylate synthase (TYMS) gene (Cho et al., 2007) or dihydropyrimidine dehydrogenase (DPD) deficiency (Meulendijks et al., 2015) tend to have increased toxicity from 5-FU.