Identification of three novel mutations in the dihydropyrimidine dehydrogenase gene associated with altered pre-mRNA splicing or protein function

Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of the pyrimidine bases uracil and thymine, as well as of the widely used chemotherapeutic drug 5-fluorouracil (5FU). Analysis of the DPD gene (DPYD) in two patients presenting with complete DPD deficiency and the parents of an affected child showed the presence of three novel mutations, including one splice site mutation IVS11 +1G --> T and the missense mutations 731A --> C (E244V) and 1651G --> A (A551T). The G --> T mutation in the invariant GT splice donor site flanking exon 11 (IVS11+1G --> T) created a cryptic splice site within exon 11. As a consequence, a 141-bp fragment encoding the aminoacid residues 400-446 of the primary sequence of the DPD protein was missing in the mature DPD mRNA. Analysis of the crystal structure of pig DPD suggested that the E244V mutation might interfere with the electron flow between NADPH and the pyrimidine binding site of DPD. The A551T point mutation might prevent binding of the prosthetic group FMN and affect folding of the DPD protein. The identification of these novel mutations in DPYD will allow the identification of patients with an increased risk of developing severe 5FU-associated toxicity.