Human polymorphism in drug metabolism: mutation in the dihydropyrimidine dehydrogenase gene results in exon skipping and thymine uracilurea.
A condition called thymine uracilurea has been described that is due to a lack of dihydropyrimidine dehydrogenase (DPD) activity. Cancer patients experiencing acute 5-fluorouracil toxicity also have lower-than-normal DPD activities. However, to date, the molecular basis of this disorder has not been addressed. In this study, the phenotype and genotype of a family that presents a patient showing no DPD activity was determined. Fibroblast mRNAs from the patient and four family members were subjected to reverse transcriptase polymerase chain reaction (RT-PCR) using primers generated from the human DPD cDNA sequence. DPD mRNA from the patient was found to lack a segment of 165 nucleotides that results from exon skipping. DPD mRNA from the parents and a sibling were found to be heterozygous for the deleted and the normal mRNA, while a brother had two normal transcripts. DPD activities and levels of DPD protein correlated with genotype; the deficient patient had no detectable DPD protein. PCR analysis of the genomic DNA from this family revealed that the defective mRNA is not due to a deletion of a portion of the gene that contains the exon, thus implying that the mutation is the result of an as yet nonidentified point mutation that causes faulty splicing.
Laboratory of Molecular Carcinogenesis, National Cancer Institute, Bethesda, MD 20892.
R
R
Meinsma
P
P
Fernandez-Salguero
A B
AB
Van Kuilenburg
A H
AH
Van Gennip
F J
FJ
Gonzalez
D001483:Base Sequence; D002478:Cells, Cultured; D002675:Child, Preschool; D042943:Dihydrouracil Dehydrogenase (NADP); D005091:Exons / Q000235:genetics*; D005260:Female; D005347:Fibroblasts / Q000737:chemistry / Q000201:enzymology; D005838:Genotype; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D009426:Netherlands; D010088:Oxidoreductases / Q000172:deficiency* / Q000235:genetics*; D010375:Pedigree; D017354:Point Mutation; D016133:Polymerase Chain Reaction / Q000379:methods; D011110:Polymorphism, Genetic; D011686:Purine-Pyrimidine Metabolism, Inborn Errors / Q000201:enzymology / Q000208:ethnology / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D017384:Sequence Deletion; D013941:Thymine / Q000378:metabolism; D014498:Uracil / Q000378:metabolism
D012333:RNA, Messenger; D014498:Uracil; D010088:Oxidoreductases; D042943:Dihydrouracil Dehydrogenase (NADP); D013941:Thymine