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Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of 5-fluorouracil (5FU). A deficiency of DPD is increasingly being recognized as the cause of an important pharmacogenetic syndrome. The importance of DPD deficiency in the aetiology of unexpected severe 5FU toxicity has been demonstrated by the fact that, in 39-59% of cases, decreased DPD activity could be detected in peripheral blood mononuclear (PBM) cells. It was observed that 55% of the patients with a decreased DPD activity suffered from grade IV neutropenia compared with 13% of the patients with a normal DPD activity (P = 0.01). Furthermore, toxicity developed significantly earlier in patients with low DPD activity than in patients with normal DPD activity (10.0 +/- 7.6 versus 19.1 +/- 15.3 days, P < 0.05). In patients suffering from severe 5FU-associated toxicity, 11 mutations have been identified in DPYD, including one splice-site mutation (IVS14 + 1G-->A), one nonsense mutation (E386X), four missense mutations (M166V, V335L, I560S, D949V) and five polymorphisms (C29R, R21Q, S534N, I543V, V732I). Considering the common use of 5FU in the treatment of cancer patients, the severe 5FU-related toxicities in patients with a low DPD activity and the high prevalence of the IVS14 + 1G-->A mutation, analysis of the DPD activity in PBM cells or screening for the IVS14 + 1G-->A mutation should be routinely carried out prior to the start of treatment with 5FU.

Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of 5-fluorouracil (5FU), and it is suggested that patients with a partial deficiency of this enzyme are at risk for developing a severe 5FU-associated toxicity. To evaluate the importance of this specific type of inborn error of pyrimidine metabolism in the etiology of 5FU toxicity, an analysis of the DPD activity, the DPD gene, and the clinical presentation of patients suffering from severe toxicity after the administration of 5FU was performed. Our study demonstrated that in 59% of the cases, a decreased DPD activity could be detected in peripheral blood mononuclear cells. It was observed that 55% of patients with a decreased DPD activity suffered from grade IV neutropenia compared with 13% of patients with a normal DPD activity (P = 0.01). Furthermore, the onset of toxicity occurred, on average, twice as fast in patients with low DPD activity as compared with patients with a normal DPD activity (10.0 +/- 7.6 versus 19.1 +/- 15.3 days; P < 0.05). Analysis of the DPD gene of 14 patients with a reduced DPD activity revealed the presence of mutations in 11 of 14 patients, with the splice site mutation IVS14+1G-->A being the most abundant one (6 of 14 patients; 43%). Two novel missense mutations 496A-->G (M166V) and 2846A-->T (D949V) were detected in exon 6 and exon 22, respectively. Our results demonstrated that at least 57% (8 of 14) of the patients with a reduced DPD activity have a molecular basis for their deficient phenotype.

Dihydropyrimidine dehydrogenase (DPD) deficiency is an autosomal recessive disease characterised by thymine-uraciluria in homozygous deficient patients and has been associated with a variable clinical phenotype. In order to understand the genetic and phenotypic basis for DPD deficiency, we have reviewed 17 families presenting 22 patients with complete deficiency of DPD. In this group of patients, 7 different mutations have been identified, including 2 deletions [295-298delTCAT, 1897delC], 1 splice-site mutation [IVS14+1G>A)] and 4 missense mutations (85T>C, 703C>T, 2658G>A, 2983G>T). Analysis of the prevalence of the various mutations among DPD patients has shown that the G-->A point mutation in the invariant splice donor site is by far the most common (52%), whereas the other six mutations are less frequently observed. A large phenotypic variability has been observed, with convulsive disorders, motor retardation and mental retardation being the most abundant manifestations. A clear correlation between the genotype and phenotype has not been established. An altered beta-alanine, uracil and thymine homeostasis might underlie the various clinical abnormalities encountered in patients with DPD deficiency.

Dihydropyrimidine dehydrogenase (DPD) is responsible for the breakdown of the widely used antineoplastic agent 5-fluorouracil (5-FU), thereby limiting the efficacy of the therapy. It has been suggested that patients suffering from 5-FU toxicities due to a low activity of DPD are genotypically heterozygous for a mutant allele of the gene encoding DPD. In this study we investigated the cDNA and a genomic region of the DPD gene of a cancer patient experiencing severe toxicity following 5-FU treatment for the presence of mutations. Although normal activity of DPD was observed in fibroblasts, the DPD activity in leucocytes of the cancer patient proved to be in the heterozygous range. Analysis of the DPD cDNA showed heterozygosity for a 165bp deletion that results from exon skipping. Sequence analysis of the genomic region encompassing the skipped exon showed that the tumour patient was heterozygous for a G-->A point mutation in the invariant GT splice donor sequence in the intron downstream of the skipped exon. So far, the G-->A point mutation has also been found in 8 out of 11 patients suffering from a complete deficiency of DPD. Considering the frequent use of 5-FU in the treatment of cancer patients, the severe 5-FU-related toxicities in patients with a low activity of DPD and the high frequency of the G-->A mutation in DPD deficient patients, analysis of the DPD activity and screening for the G-->A mutation should be routinely carried out prior to the start of the treatment with 5-FU.

Dihydropyrimidine dehydrogenase catalyzes the first and rate-limiting step in the breakdown of thymine, uracil, and the widely used antineoplastic drug, 5-fluorouracil. Sequence analysis of the dihydropyrimidine dehydrogenase cDNA in a Dutch consanguineous family identified a novel four-base deletion (delTCAT296-299) leading to premature termination of translation. The deletion is located in a TCAT tandem-repeat sequence and most likely results from unequal crossing-over or slipped mispairing. In this family we identified three homozygous individuals for this mutation. Two of these showed convulsive disorders but one was clinically normal. This observation suggests that, at least in this family, there is no clear correlation between the dihydropyrimidine dehydrogenase genotype and phenotype.

Dihydropyrimidine dehydrogenase (DPD) deficiency is an autosomal recessive disease characterized by thymine-uraciluria and associated with a variable clinical phenotype. In order to identify the molecular defect underlying complete DPD deficiency in a Dutch patient previously shown to have a 165 base pair deletion in the mature DPD mRNA, we cloned the genomic region encompassing the skipped exon and its flanking intron sequences. Sequence analysis revealed that the patient was homozygous for a single G-->A point mutation in the invariant GT dinucleotide splice donor site downstream of the skipped exon. The same mutation was identified in another, unrelated, Dutch patient. Because this mutation destroys a unique MaeII restriction site, rapid screening using restriction enzyme cleavage of the amplified genomic region encompassing this mutation is possible. Analysis of 50 controls revealed no individuals heterozygous for this mutation.

In the urine of a child with unexplained convulsions large amounts of uracil and thymine were detected by gas chromatography. Identification was performed by coupled gas chromatography-mass spectrometry. Quantitation of the urinary excretion by means of a sensitive high-performance liquid chromatographic (HPLC) method revealed a 1000-fold elevation compared to normal. Serum and cerebrospinal fluid levels of the two pyrimidine bases were about a hundred times higher than normal. In fibroblasts the activity of dihydrothymine dehydrogenase was determined by measuring the conversion of radioactive labelled thymine to dihydrothymine with HPLC of the reaction mixture. In the patient's cells a complete deficiency of dihydrothymine dehydrogenase activity was found. Our patient is the first case described with such a proven enzyme deficiency.

A family with dihydropyrimidine dehydrogenase (DPD) deficiency is presented. In 3 persons a complete deficiency, and in 3 others a partial deficiency was detected in cultured fibroblasts. Two homozygote subjects and 1 heterozygote subject suffered from epileptic manifestations, in one of these homozygote subjects also microcephaly was found. DPD deficiency might be an etiological factor in the clinical picture of these patients. An autosomal recessive mode of inheritance of this deficiency was found.