Prevalence of a common point mutation in the Dihydropyrimidine dehydrogenase (DPD) gene within the 5 '-splice donor site of intron 14 in patients with severe 5-fluorouracil (5-FU)-related toxicity compared with controls

Deficiency of dihydropyrimidine dehydrogenase (DPD), the rate-limiting enzy me in 5-fluorouracil (5-FU) catabolism, has been linked to toxic side effec ts of 5-FU. The most prominent mutation of the DPD gene resulting in severe DPD deficiency is a G to A mutation in the GT 5 ' -splice recognition site of intron 14 (exon 14-skipping mutation). The corresponding mRNA lacks exo n 14, and the enzymatic activity of the translated DPD protein is virtually absent. We developed a reverse transcription-PCR-based assay suitable for routine identification of the exon 14-skipping mutation and screened a cont rol cohort of 851 Caucasian individuals as well as a cohort of 25 cancer pa tients reported by their physicians to have suffered from WHO grades 3-4 to xicity upon 5-FU chemotherapy. Within the control cohort, in total, eight h eterozygotes were detected (0.94%): one heterozygote in 51 healthy donors, (1.96%); Five heterozygotes in 572 hospital patients (0.87%); and two heter ozygotes in 228 colorectal tumor patients (0.88%). Among the 25 patients wi th severe 5-FU-related toxicity, 5 (20%) were heterozygous and 1 (4%) was h omozygous for the exon 14-skipping mutation. All six patients had experienc ed WHO grade 4 myelosuppression. Lethal outcome was seen in the homozygous and two of the heterozygous cases. We conclude that carriers of the DPD exo n 14-skipping mutation are at significantly increased risk to experience li fe-threatening myelosuppression upon 5-FU treatment, even when the allelic status is heterozygous. These data lead us to suggest routine testing for t he exon 14-skipping mutation before 5-FU treatment.