Identification of purine nucleoside phosphorylase deficiency in dried blood spots by a non-radiochemical assay using reversed-phase high-performance liquid chromatography

Purine nucleoside phosphorylase (PNP) deficiency results in severe T cell dysfunction and hypouricemia. An assay to measure PNP activity in dried blood spots was developed using reversed-phase HPLC. The assay was linear with reaction times between 5 and 12.5 minutes, and protein concentrations ranging from 0.4 to 1.8 mg/ml. The intra-assay CV and the inter-assay CV for the complete assay was <3.6%. The PNP activity in a control blood spot, stored at 4 degrees C, remained stable for at least one year. In a patient suffering from a PNP deficiency, the residual PNP activity was only 0.3% compared to that observed in controls (1431 +/- 238 nmol/mg/h, n = 114). The PNP activity (483 +/- 35 nmol/mg/h, n = 3) in heterozygotes for the c.614A > C mutation (p.E205A) in the PNP gene was 34% compared to controls. Thus, the analysis of the PNP activity in blood spots can readily detect patients with a PNP deficiency.

Determination of adenosine deaminase activity in dried blood spots by a nonradiochemical assay using reversed-phase high-performance liquid chromatography

Adenosine deaminase (ADA) deficiency is a rare metabolic disease causing severe combined immunodeficiency (SCID). An assay to determine ADA activity in dried blood spots was developed using reversed-phase HPLC. The assay was linear with reaction times up to at least 4 hours, and protein concentrations up to at least 2.2 mg/ml. The intra-assay CV and the inter-assay CV for the complete assay was 3.5 and 8.4%, respectively. The ADA activity in a control blood spot, stored at 4 degrees C, remained stable for at least one year. Only a slightly decreased ADA activity (35 +/- 13 nmol/mg/h, n = 4) was observed in heterozygotes for a c.704G > A mutation in the ADA gene when compared to that observed in controls (41 +/- 13 nmol/mg/h, n = 108). In addition, increased ADA activity as found in a rare form of congenital anemia can be assessed, as observed in a bloodspot from a patient diagnosed with Diamond Blackfan anemia (ADA activity 150 nmol/mg/h).

Dihydropyrimidine dehydrogenase deficiency caused by a novel genomic deletion c.505_513del of DPYD

Dihydropyrimidine dehydrogenase (DPD) deficiency is an autosomal recessive disorder of the pyrimidine degradation pathway. In a patient presenting with convulsions, psychomotor retardation and Reye like syndrome, strongly elevated levels of uracil and thymine were detected in urine. No DPD activity could be detected in peripheral blood mononuclear cells. Analysis of the gene encoding DPD (DPYD) showed that the patient was homozygous for a novel c.505_513del (p.169_171del) mutation in exon 6 of DPYD.

Beta-ureidopropionase deficiency presenting with congenital anomalies of the urogenital and colorectal systems

Beta-ureidopropionase deficiency (McKusick 606673) is an autosomal recessive condition caused by mutations in the UPB1 gene. To date, five patients have been reported, including one putative case detected through newborn screening. Clinical presentation includes neurological and developmental problems. Here, we report another case of beta-ureidopropionase deficiency who presented with congenital anomalies of the urogenital and colorectal systems and with normal neurodevelopmental milestones. Analysis of a urine sample, because of the suspicion of renal stones on ultrasound, showed strongly elevated levels of the characteristic metabolites, N-carbamyl-beta-amino acids. Subsequent analysis of UPB1 identified a novel mutation 209 G>C (R70P) in exon 2 and a previously reported splice receptor mutation IVS1-2A>G. Expression studies of the R70P mutant enzyme showed that the mutant enzyme did not possess any residual activity. Long-term follow-up is required to determine the clinical significance of the beta-ureidopropionase deficiency in our patient.

Determination of thymidine phosphorylase activity in human blood cells and fibroblasts by a nonradiochemical assay using reversed-phase high-performance liquid chromatography

In this study, we demonstrated that the highest activity of thymidine phosphorylase (TP) was found in peripheral blood mononuclear (PBM) cells followed by that of thrombocytes and granulocytes whereas no activity of TP could be detected in erythrocytes. The activity of TP in leukocytes proved to be intermediate compared to the TP activity observed in PBM cells and granulocytes. The activity of TP also was readily detectable in human fibroblasts.

Lethal outcome of a patient with a complete dihydropyrimidine dehydrogenase (DPD) deficiency after administration of 5-fluorouracil: frequency of the common IVS14+1G>A mutation causing DPD deficiency

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 from developing a severe 5FU-associated toxicity. In this study, we demonstrated that a lethal toxicity after a treatment with 5FU was attributable to a complete deficiency of DPD. Analysis of the DPD gene for the presence of mutations showed that the patient was homozygous for a G-->A mutation in the invariant GT splice donor site flanking exon 14 (IVS14+1G>A). As a consequence, no significant residual activity of DPD was detected in peripheral blood mononuclear cells. To determine the frequency of the IVS14+1G>A mutation in the Dutch population, we developed a novel PCR-based method allowing the rapid analysis of the IVS14+1G>A mutation by RFLP. Screening for the presence of this mutation in 1357 Caucasians showed an allele frequency of 0.91%. In our view, the apparently high prevalence of the IVS14+1G>A mutation in the normal population, with 1.8% heterozygotes, warrants genetic screening for the presence of this mutation in cancer patients before the administration of 5FU.

Clinical implications of dihydropyrimidine dehydrogenase (DPD) deficiency in patients with severe 5-fluorouracil-associated toxicity: identification of new mutations in the DPD gene

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.