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.
Meinsma
R
R
Laboratory of Molecular Carcinogenesis, National Cancer Institute, Bethesda, MD 20892.
Fernandez-Salguero
P
P
Van Kuilenburg
A B
AB
Van Gennip
A H
AH
Gonzalez
F J
FJ
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