DPYD and dihydropyrimidine dehydrogenase deficiency: Four studies 43, 49, 51, 53 reported the functional characterization of several DPYD variants—including a number of rare and novel variants—that were identified by sequencing all exons and flanking intronic regions of DPYD gene using the Sanger method in a group of patients with DPD deficiency, who developed early-onset severe toxicity.