5-fluorocytosine-related bone-marrow depression and conversion to fluorouracil: a pilot study

The aim of this study is to investigate whether fluorouracil (5-FU) could be responsible for bone-marrow depression occurring in fluorocytosine 5-FC) treated patients. Six 5-FC treated patients were included in this pilot study. Toxicity was monitored by means of thrombocyte and leucocyte counts. 5-FC and 5-FU serum levels were measured using a high-performance liquid chromatography (HPLC) assay that allows simultaneous determination of both compounds. The amounts of 5-FU in the 34 available serum samples remained below the limit of quantitation ( <0.05 mg/L), whereas 5-FC levels could be detected in all samples. Instead, low levels of the 5-FU catabolite alpha-fluoro-beta-alanine (FBAL) were detected in several of the investigated serum samples. In case of three patients thrombocyte counts remained within the normal range during 5-FC treatment, whereas one patient developed thrombocytopenia (50 x 10(9) thrombocytes/L) during therapy. Furthermore, one patient developed leucocytopenia (2.6 x 10(9) leucocytes/L) during 5-FC therapy, whereas the remaining five patients were suffering from leucocytosis prior to 5-FC therapy. In conclusion, we found nondetectable 5-FU serum concentrations ( <0.05 mg/L) in ICU patients treated with intravenous 5-FC, making it unlikely that 5-FC associated toxicity results from 5-FU exposure in patients receiving intravenous 5-FC therapy. These findings may be explained by the fact that our patients received 5-FC intravenously instead of orally, therefore not allowing active conversion of 5-FC to 5-FU by the human intestinal microflor

Investigation of IVS14+ 1G > A polymorphism of DPYD gene in a group of Turkish patients with colorectal cancer

BACKGROUND: Dihydropyrimidine dehydrogenase (DPD) is a critical enzyme in the catabolism of 5-fluorouracil (5-FU), a drug frequently used in cancer therapy. One of the possible causes of severe 5-FU toxicity is genetic polymorphisms in the DPYD gene, such as IVS14+1G > A. In this study we aimed to investigate the frequency of the IVS14+1G > A mutation in the DPYD gene in Turkish patients with colorectal cancer (CRC) and healthy controls. MATERIALS AND METHODS: Blood samples were collected from 218 individuals (56 patients with CRC and 162 healthy individuals), and the DNA was isolated. A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was used to detect the frequency of the IVS14+1G > A mutation in our population. RESULTS: The IVS14+1G > A mutation (heterozygous) in the DPYD gene was identified in two healthy subjects in this Turkish population. CONCLUSION: The apparently high prevalence (allele frequency of 0.6%) of the IVS14+1G > A mutation warrants genetic screening for this mutation in cancer patients before the administration of 5-F

Atypical presentation of Arts syndrome due to a novel hemizygous loss-of-function variant in the PRPS1 gene

The PRPS1 gene, located on Xq22.3, encodes phosphoribosyl-pyrophosphate synthetase (PRPS), a key enzyme in de novo purine synthesis. Three clinical phenotypes are associated with loss-of-function PRPS1 variants and decreased PRPS activity: Arts syndrome (OMIM: 301835), Charcot-Marie-Tooth disease type 5 (CMTX5, OMIM: 311070), and nonsyndromic X-linked deafness (DFN2, OMIM: 304500). Hearing loss is present in all cases. CMTX5 patients also show peripheral neuropathy and optic atrophy. Arts syndrome includes developmental delay, intellectual disability, ataxia, and susceptibility to infections, in addition to the above three features. Gainof-function PRPS1 variants result in PRPS superactivity (OMIM: 300661) with hyperuricemia and gout. We report a 6-year-old boy who presented with marked generalized muscular hypotonia, global developmental delay, lack of speech, trunk instability, exercise intolerance, hypomimic face with open mouth, oropharyngeal dysphagia, dysarthria, and frequent upper respiratory tract infections. However, his nerve conduction velocity, audiologic, and funduscopic investigations were normal. A novel hemizygous variant, c.130A &gt; G p.(Ile44Val), was found in the PRPS1 gene by panel sequencing. PRPS activity in erythrocytes was markedly reduced, confirming the pathogenicity of the variant. Serum uric acid and urinary purine and pyrimidine metabolite levels were normal. In conclusion, we present a novel PRPS1 loss-of-function variant in a patient with some clinical features of Arts syndrome, but lacking a major attribute, hearing loss, which is congenital/early-onset in all other reported Arts syndrome patients. In addition, it is important to acknowledge that normal levels of serum and urinary purine and pyrimidine metabolites do not exclude PRPS1-related disorders

Beta-ureidopropionase deficiency presenting with febrile status epilepticus

Beta-ureidopropionase is the third enzyme in the catabolic pathway of uracil and thymine. To date, only three other patients are reported with this inborn error of metabolism. We report the clinical presentation of a male patient who presented at the age of 4 months after an ALTE-like event (ALTE = acute life-threatening event) with febrile status epilepticus. Such a clinical presentation has not been reported before in this condition. Diagnosis was based on biochemical, enzymatic and molecular studies. MRI (magnetic resonance imaging) at the age of 11 months demonstrated large subdural hematomata and global supratentorial atrophy. At that time the patient showed severe psychomotor retardation with muscular hypotonia, extremely limited visual contact and poorly controlled epilepsy. CONCLUSIONS: Pyrimidine degradation defects should be included in the differential diagnosis of convulsions, (febrile) status epilepticus, psychomotor retardation and possibly also ALTE-like event

Clinical, biochemical and genetic findings in two siblings with a dihydropyrimidinase deficiency

Dihydropyrimidinase (DHP) is the second enzyme of the pyrimidine degradation pathway and it catalyses the ring opening of 5,6-dihydrouracil and 5,6-dihydrothymine to N-carbamyl-beta-alanine and N-carbamyl-beta-aminoisobutyric acid, respectively. To date, only nine individuals have been reported suffering from a complete DHP deficiency. We report two siblings presenting with strongly elevated levels of 5,6-dihydrouracil and 5,6-dihydrothymine in plasma, cerebrospinal fluid and urine. One of the siblings had a severe delay in speech development and white matter abnormalities, whereas the other one was free of symptoms. Analysis of the DHP gene (DPYS) showed that both patients were compound heterozygous for the missense mutation 1078T>C (W360R) in exon 6 and a novel missense mutation 1235G>T (R412M) in exon 7. Heterologous expression of the mutant enzymes in Escherichia coli showed that both missense mutations resulted in a mutant DHP enzyme without residual activity. Analysis of the crystal structure of eukaryotic DHP from the yeast Saccharomyces kluyveri and the slime mold Dictyostelium discoideum suggests that the W360R and R412M mutations lead to structural instability of the enzyme which could potentially impair the assembly of the tetrame

Phosphoribosylpyrophosphate synthetase superactivity and recurrent infections is caused by a p.Val142Leu mutation in PRS-I

We identified a novel missense mutation, c.424G>C (p.Val142Leu) in PRPS1 in a patient with uric acid overproduction without gout but with developmental delay, hypotonia, hearing loss, and recurrent respiratory infections. The uric acid overproduction accompanying this combination of symptoms suggests that the patient presented with phosphoribosylpyrophosphate (PRPP) synthetase superactivity, but recurrent infections have not been associated with superactivity until now. However, recurrent infections are a prominent feature of patients with Arts syndrome, which is caused by PRPS1 loss-of-function mutations, indicating that the patient reported here has an intermediate phenotype. Molecular modeling predicts that the p.Val142Leu change affects both allosteric sites that are involved in inhibition of PRPS1 and the ATP-binding site, which suggests that this substitution can result both in a gain-of-function and loss-of-function of PRPP synthetase. This finding is in line with the normal PRPP synthetase activity in fibroblasts and the absence of activity in erythrocytes of the present patient. We postulate that the overall effect of the p.Val142Leu change on protein activity is determined by the cell type, being a gain-of-function in proliferating cells and a loss-of-function in postmitotic cells. Our results show that missense mutations in PRPS1 can cause a continuous spectrum of features ranging from progressive non-syndromic postlingual hearing impairment to uric acid overproduction, neuropathy, and recurrent infections depending on the functional sites that are affected. (C) 2012 Wiley Periodicals, Inc