Molecular basis of the human dihydropyrimidine dehydrogenase deficiency and 5-fluorouracil toxicity.

Abstract

Dihydropyrimidine dehydrogenase (DPD) deficiency constitutes an inborn error in pyrimidine metabolism associated with thymine-uraciluria in pediatric patients and an increased risk of toxicity in cancer patients receiving 5-fluorouracil (5-FU) treatment.The molecular basis for DPD deficiency in a British family having a cancer patient that exhibited grade IV toxicity 10 d after 5-FU treatment was analyzed.A 165-bp deletion spanning a complete exon of the DPYD gene was found in some members of the pedigree having low DPD catalytic activity.Direct sequencing of lymphocyte DNA from these subjects revealed the presence of a G to A point mutation at the 5 Ј -splicing site consensus sequence (GT to AT) that leads to skipping of the entire exon preceding the mutation during pre-RNA transcription and processing.A PCR-based diagnostic method was developed to determine that the mutation is found in Caucasian and Asian populations.This mutation was also detected in a Dutch patient with thymine-uraciluria and completely lacking DPD activity.A genotyping test for the G to A splicing point mutation could be useful in predicting cancer patients prone to toxicity upon administration of potentially toxic 5-FU and for genetic screening of heterozygous carriers and homozygous deficient subjects.( J. Clin.Invest.1996.98:610-615.)Key words: DPD deficiency • 5-FU toxicity • population genotyping • exon skipping MethodsFamily pedigree.Blood samples from a British family were collected after a family member displayed excessive 5-FU toxicity during chemotherapy.This family is unrelated to any family with DPD defi-