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Dihydropyrimidinase deficiency: structural organization, chromosomal localization, and mutation analysis of the human
N Hamajima1, M Kouwaki, P Vreken
1Department of Pediatrics, Nagoya City University Medical School, Nagoya City Higashi General Hospital, Nagoya, Japan. hamajima@med.nagoya-cu.ac.jp
Abstract:
Dihydropyrimidinase (DHP) deficiency (MIM 222748) is characterized by dihydropyrimidinuria and is associated with a variable clinical phenotype. This disease might be associated with a risk of 5-fluorouracil toxicity, although no cases have been reported. We present here both the molecular characterization of the human DHP gene and, for the first time, the mutations causing DHP deficiency. The human DHP gene spans >80 kb and consists of 10 exons. It has been assigned to 8q22, by FISH. We performed mutation analysis of genomic DNA in one symptomatic and five asymptomatic individuals presenting with dihydropyrimidinuria. We identified one frameshift mutation and five missense mutations. Two related Japanese adult subjects were homozygous for the Q334R substitution, whereas two other, unrelated Japanese infant subjects were heterozygous for the same mutation, but this mutation is not common in the Japanese population. A Caucasian pediatric patient exhibiting epileptic attacks, dysmorphic features, and severe developmental delay was homozygous for W360R. Using a eukaryotic expression system, we showed that all mutations reduced enzyme activity significantly, indicating that these are crucial DHP deficiency-causing mutations. There was no significant difference, in residual activity, between mutations observed in the symptomatic and those observed in the asymptomatic individuals.
Insights
Dihydropyrimidinase (DHP) deficiency, a genetic disorder causing dihydropyrimidinuria, is linked to mutations in the DHP gene. These mutations significantly reduce enzyme activity, impacting patients with variable clinical outcomes.
Area of Science:
- Biochemistry
- Genetics
- Molecular Biology
Background:
- Dihydropyrimidinase (DHP) deficiency is a genetic disorder characterized by dihydropyrimidinuria and variable clinical presentations.
- The potential association with 5-fluorouracil toxicity is noted, though not yet documented.
- Understanding the genetic basis of DHP deficiency is crucial for diagnosis and management.
Purpose of the Study:
- To perform molecular characterization of the human DHP gene.
- To identify mutations responsible for DHP deficiency.
- To investigate the functional impact of identified mutations on enzyme activity.
Main Methods:
- Mutation analysis of genomic DNA from symptomatic and asymptomatic individuals with dihydropyrimidinuria.
- Fluorescence in situ hybridization (FISH) for gene localization.
- Eukaryotic expression system to assess the effect of mutations on DHP enzyme activity.
Main Results:
- The human DHP gene, spanning over 80 kb with 10 exons, was assigned to chromosome 8q22.
- One frameshift and five missense mutations were identified in patients.
- All identified mutations significantly reduced DHP enzyme activity, regardless of clinical phenotype.
Conclusions:
- Identified mutations in the DHP gene are causative of DHP deficiency.
- The severity of DHP deficiency is not directly correlated with residual enzyme activity.
- Further research may elucidate the variable clinical phenotypes associated with DHP deficiency.