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Biomedical subjects

N Blau

Publications and source records attributed to N Blau.

At least 37 records · Page 2Linked to original sources
PubMed2001

Pediatric urolithiasis in Armenia: a study of 198 patients observed from 1991 to 1999.

To study prospectively the risk factors and etiology of urolithiasis in all stone patients aged <15 years admitted from 1991 to 1999 to the Arabkir hospital in Yerevan. Stones were obtained by surgery (64%), extracorporeal shockwave lithotripsy (ESWL) (7%) or cystoscopic extraction (4%); 25% passed spontaneously. All were examined by infrared spectroscopy, and spot urines were analyzed chemically. 198 patients, 180 (68% males) with renal stones and 18 (83% males) with primary bladder stones, were studied. Calcium oxalate (CaOx) was the predominant constituent in 62% of the kidney stones, followed by struvite (17%), calcium phosphate (7%), uric acid (7%), ammonium acid urate (5%), and cystine (2%). Bladder stones contained CaOx in 72%, uric acid in 22% and ammonium acid urate in 6% of patients. Etiology was obviously metabolic in 5% and possibly metabolic in 26%. Twenty percent of stones were infectious, and 19% were endemic (9% bladder and 10% kidney stones); 4% were secondary to urinary stasis with malformation but no infection. Etiology in 26% remained unknown. Stone composition and metabolic etiology are similar to that in central Europe and North America. In contrast, infectious calculi and particularly endemic stones are still common, although becoming less so now. Urolithiasis in Armenia thus reflects the transition from a rural to an urban society.

Adolescent↗
PubMed2001

A splice mutation in the GTP cyclohydrolase I gene causes dopa-responsive dystonia by exon skipping.

Four different mutations in the GTP cyclohydrolase I gene were found (P199L, M211V, IVS5+1G>A, G203R) in 6 out of 33 families with dopa-responsive dystonia. A splice mutation (IVS5+1G>A) located at the border of exon 5 to intron 5 was found in one of these families. Three members of the family carry the IVS5+1G>A mutation on one allele, inherited from the father to the daughter and son. Examination of the mRNA showed an exon 5 skipping that results in a reduction of enzyme activity in cultured fibroblasts to 4-17% compared to controls. The father and daughter never had clinical symptoms of dopa-responsive dystonia. The son was symptomatic at the age of 3 years and was treated successfully with L-dopa/carbidopa. After 20 years this therapy was terminated and for the next 6 years he was free of symptoms. With increased motoric activity, symptoms reappeared and the therapy was reintroduced.

Alleles↗
PubMed2001

Tetrahydrobiopterin-responsive phenylalanine hydroxylase deficiency in Dutch neonates.

Four neonates with a positive phenylalanine screening test (Phe concentrations between 258 and 1250 micromol/L) were investigated further to differentiate between phenylalanine hydroxylase (PAH) deficiency and variant hyperphenylalaninaemia (HPA) forms. In patients 1 and 2 a tetrahydrobiopterin (BH4) load caused a significant decrease of the plasma Phe levels. A combined phenylalanine/BH4 loading test was performed in patients 2, 3 and 4. In the latter two patients, plasma Phe concentrations completely normalized within 8 h after the BH4 load (20 mg/kg). Basal urinary pterins were normal in all four patients. The activity of dihydropteridine reductase (DHPR) was normal in patients 1, 2 and 3 and 50% of control values in patient 4 (not in the range of DHPR-deficient patients). In patient 3 a subsequent phenylalanine loading test with concomitant analysis of plasma biopterins revealed a normal increase of biopterin, excluding a BH4 biosynthesis defect. Pterins and neurotransmitter metabolites in CSF of patients 1, 3 and 4 were normal. DNA mutations detected in the PAH gene of patients 1-4 were A313T, and L367fsinsC; V190A and R243X; A300S and A403V; R241C and A403V. The results are suggestive for mutant PAH enzymes with decreased affinity for the cofactor BH4.

Biopterins↗
PubMed2001

Epidermal H(2)O(2) accumulation alters tetrahydrobiopterin (6BH4) recycling in vitiligo: identification of a general mechanism in regulation of all 6BH4-dependent processes?

It has been shown in vivo that patients with the depigmentation disorder vitiligo accumulate hydrogen peroxide (H(2)O(2)) accompanied by low catalase levels and high concentrations of 6- and 7-biopterin in their epidermis. Earlier it was demonstrated that epidermal 4a-OH-tetrahydrobiopterin dehydratase, an important enzyme in the recycling process of 6(R)-L-erythro 5,6,7,8 tetrahydrobiopterin (6BH(4)), has extremely low activities in these patients concomitant with a build-up of the abiogenic 7-isomer (7BH(4)), leading to competitive inhibition of epidermal phenylalanine hydroxylase. A topical substitution for the impaired epidermal catalase with a pseudocatalase effectively removes epidermal H(2)O(2), yielding a recovery of epidermal 4a-OH-tetrahydrobiopterin dehydratase activities and physiologic 7BH(4) levels in association with successful repigmentation demonstrating recovery of the 6BH(4) recycling process. Examination of recombinant enzyme activities, together with 4a-OH-tetrahydrobiopterin dehydratase expression in the epidermis of untreated patients, identifies H(2)O(2)-induced inactivation of this enzyme. These results are in agreement with analysis of genomic DNA from these patients yielding only wild-type sequences for 4a-OH-tetrahydrobiopterin dehydratase and therefore ruling out the previously suspected involvement of this gene. Furthermore, our data show for the first time direct H(2)O(2) inactivation of the important 6BH(4) recycling process. Based on this observation, we suggest that H(2)O(2) derived from various sources could be a general mechanism in the regulation of all 6BH(4)-dependent processes.

Biopterins↗
PubMed2001

Diagnosis of dopa-responsive dystonia and other tetrahydrobiopterin disorders by the study of biopterin metabolism in fibroblasts.

BACKGROUND: Dopa-responsive dystonia (DRD) and tetrahydrobiopterin (BH4) defects are inherited disorders characterized by monoamine neurotransmitter deficiency with decreased activity of one of the BH4-metabolizing enzymes. The aim of the study was to determine the utility of cultured skin fibroblasts for the diagnosis of these diseases. METHODS: Neopterin and biopterin production and GTP cyclohydrolase I (GTPCH) activity were measured in cytokine-stimulated fibroblasts; 6-pyruvoyltetrahydropterin synthase (PTPS), sepiapterin reductase (SR), and dihydropteridine reductase (DHPR) activities were measured in unstimulated fibroblasts. We examined 8 patients with DRD, 3 with autosomal recessive GTPCH deficiency, 7 with PTPS deficiency, 3 with DHPR deficiency, and 49 controls (35 fibroblast and 14 amniocyte samples). RESULTS: Fibroblasts from patients with DRD and autosomal recessive GTPCH deficiency showed reduced GTPCH activity (15.4% and 30.7% of normal activity, respectively) compared with controls (P < 0.001). Neopterin production was very low and biopterin production was reduced in both disorders. PTPS- and DHPR-deficient cells showed no enzyme activities; in PTPS deficiency the pattern of pterin production was typical (neopterin, 334-734 pmol/mg; controls, 18-98 pmol/mg; biopterin, 0 pmol/mg; controls, 154-303 pmol/mg). Reference values of all enzyme activities and pterin production were measured in fibroblasts and also in amniocytes for prenatal diagnosis. CONCLUSIONS: Cultured skin fibroblasts are a useful tool in the diagnosis of BH4 deficiencies. Intracellular neopterin and biopterin concentrations and GTPCH activity in cytokine-stimulated fibroblasts are particularly helpful in diagnosing patients with DRD.

Alcohol Oxidoreductases↗
PubMed2000

Tetrahydrobiopterin biosynthesis, regeneration and functions.

Tetrahydrobiopterin (BH(4)) cofactor is essential for various processes, and is present in probably every cell or tissue of higher organisms. BH(4) is required for various enzyme activities, and for less defined functions at the cellular level. The pathway for the de novo biosynthesis of BH(4) from GTP involves GTP cyclohydrolase I, 6-pyruvoyl-tetrahydropterin synthase and sepiapterin reductase. Cofactor regeneration requires pterin-4a-carbinolamine dehydratase and dihydropteridine reductase. Based on gene cloning, recombinant expression, mutagenesis studies, structural analysis of crystals and NMR studies, reaction mechanisms for the biosynthetic and recycling enzymes were proposed. With regard to the regulation of cofactor biosynthesis, the major controlling point is GTP cyclohydrolase I, the expression of which may be under the control of cytokine induction. In the liver at least, activity is inhibited by BH(4), but stimulated by phenylalanine through the GTP cyclohydrolase I feedback regulatory protein. The enzymes that depend on BH(4) are the phenylalanine, tyrosine and tryptophan hydroxylases, the latter two being the rate-limiting enzymes for catecholamine and 5-hydroxytryptamine (serotonin) biosynthesis, all NO synthase isoforms and the glyceryl-ether mono-oxygenase. On a cellular level, BH(4) has been found to be a growth or proliferation factor for Crithidia fasciculata, haemopoietic cells and various mammalian cell lines. In the nervous system, BH(4) is a self-protecting factor for NO, or a general neuroprotecting factor via the NO synthase pathway, and has neurotransmitter-releasing function. With regard to human disease, BH(4) deficiency due to autosomal recessive mutations in all enzymes (except sepiapterin reductase) have been described as a cause of hyperphenylalaninaemia. Furthermore, several neurological diseases, including Dopa-responsive dystonia, but also Alzheimer's disease, Parkinson's disease, autism and depression, have been suggested to be a consequence of restricted cofactor availability.

Alcohol Oxidoreductases↗
PubMed2000

Isolated central form of tetrahydrobiopterin deficiency associated with hemizygosity on chromosome 11q and a mutant allele of PTPS.

6-Pyruvoyl-tetrahydropterin synthase (PTS or PTPS) is involved in tetrahydrobiopterin (BH(4)) biosynthesis, the cofactor for various enzymes including the aromatic amino acid hydroxylases. Inherited PTPS deficiency is a heterogeneous disease with different phenotypes leading to BH(4) depletion. The severe form of PTPS deficiency causes hyperphenylalaninemia and monoamine neurotransmitter deficiency, whereas the mild form gives rise to hyperphenylalaninemia only. From 228 patients with PTPS deficiency at least 32 different mutant alleles have been identified on its corresponding gene, located on chromosome 11q22.3-q23.3. Here we describe a new allele from a child with PTPS deficiency who exhibited a mild but transient form of hyperphenylalaninemia, yet was deficient in CSF monoamines. The patient was found to carry, on her genomic DNA and cDNA, a homozygous A>G transition, leading to PTPS codon alteration Tyr99 to Cys (Y99C). The mother and several members of the maternal family were carriers of the Y99C allele, also verified by the reduced PTPS enzyme activity in erythrocytes. By cytogenetic, molecular, and FISH analyses, a de novo deletion spanning from 11q14 to 11q23.3 on the patient's paternal chromosome was mapped, establishing hemizygosity of the Y99C allele. The PTPS mutation observed in this patient generates a novel phenotype with an apparently isolated central form of BH(4) deficiency.

Alleles↗
PubMed2000

Evaluation of urinary acylglycines by electrospray tandem mass spectrometry in mitochondrial energy metabolism defects and organic acidurias.

We analyzed the urinary acylglycine excretion in 26 patients with mitochondrial energy metabolism disorders and in 55 patients with organic acidurias by electrospray tandem mass spectrometry (ESI-MS/MS), monitoring precursor ions of m/z 90. Urinary concentrations of the different acylglycines were quantified using deuterated internal standards. Normal values for the most important acylglycines were established. In MCAD and MAD (neonatal form) deficiencies, typical excretion patterns of urinary acylglycines were found in all the samples. In isovaleric aciduria, propionic aciduria, and 3-methylcrotonylglycinuria typical glycine conjugates were always found. Methylmalonic aciduria (mutase deficiency), multiple carboxylase deficiency, and 3-hydroxy-3-methylglutaric aciduria revealed pathological acylglycine profiles, even if not specific for the disease. In all these diseases acylglycine excretion seems to be less influenced by the clinical status than organic acid excretion. This method is a useful diagnostic tool for these metabolic disorders, complementary to organic acids and acylcarnitine profiles.

Acyl-CoA Dehydrogenase↗
PubMed2000

Hyperphenylalaninemia and 7-pterin excretion associated with mutations in 4a-hydroxy-tetrahydrobiopterin dehydratase/DCoH: analysis of enzyme activity in intestinal biopsies.

Hyperphenylalaninemia, which can cause neurological disorders and mental retardation, results from a mutation in phenylalanine hydroxylase or an enzyme required for biosynthesis or regeneration of its cofactor, tetrahydrobiopterin. The hyperphenylalaninemia variant primapterinuria is characterized by the excretion of 7-biopterin (primapterin). This disorder is thought to be due to a deficiency of 4a-hydroxy-tetrahydrobiopterin dehydratase (pterin-4a-carbinolamine dehydratase), but a lack of tissue activity has not been directly demonstrated. The five mutations so far recognized in patients with primapterinuria are associated with either a single amino acid change or a premature stop codon. Only C81R has been successfully expressed in soluble form, and was found to have 40% of normal activity. Tissues which could be obtained by minimally invasive procedures were analyzed for dehydratase activity. None was detected in normal human white cells or fibroblasts. However, activity was found in intestine of rat, dog, pig, and particularly humans where it was only eight times lower than in liver. Distribution along the length and across the wall of small intestine was relatively uniform. Moreover, the dehydratases from human liver and intestinal mucosa have identical kinetic properties. A biopsy of duodenal mucosa from a patient with homozygous E96K dehydratase had activity of 55 nmol. min(-1)g(-1) mucosa compared to 329 +/- 32 nmol. min(-1)g(-1) tissue in controls (n = 12). The sixfold lower tissue activity of the E96K mutant alone may not be sufficient to account for the biochemical symptoms of primapterinuria in this patient. However, accumulation of a 4a-hydroxy-tetrahydrobiopterin degradation product (a side-chain cyclic adduct), which has been observed in vitro and appears to be a dehydratase inhibitor, may further exacerbate the problem.

Adolescent↗
PubMed2000

Diagnostic potential of neutrophil elastase inhibitor complex in the routine care of critically ill newborn infants.

UNLABELLED: It has been suggested that determination of the neutrophil elastase alpha1-proteinase inhibitor complex (E-alpha1PI) improves the diagnosis of bacterial infection in newborns. We evaluated the use of E-alpha1PI measurements in 143 newborns, consecutively admitted to a tertiary intensive care unit, employing a new random access assay and a sampling procedure that minimises post-collection artefacts. The 95% range for noninfected newborns was 20-110 microg/l up to the 5th day of life and 20-85 microg/l thereafter. The sensitivity as to the diagnosis of culture-proven bloodstream infection was 80% for E-alpha1PI, 86% for the immature to total neutrophil ratio, 64% for C-reactive protein and 37% for the total white blood cell count. The corresponding specificity amounted to 97%, 85%, 85% and 86%, respectively. E-alpha1PI increases preceded elevations of C-reactive protein by 18 h. Like C-reactive protein, E-alpha1PI levels did not distinguish between bloodstream infection and non-bacterial inflammatory responses. Results of E-alpha1PI became available within 1 h of collection and usually 2-3 h before manual leucocyte counts. CONCLUSION: Determination of neutrophil elastase alpha1-proteinase inhibitor levels yields diagnostic advantages comparable to those of manual differential counts but provide faster turnaround times.

Cohort Studies↗
PubMed2000

The neurochemistry of phenylketonuria.

UNLABELLED: The mechanisms by which deficiency of hepatic phenylalanine hydroxylase causes central nervous system disease are reviewed. The neurological disease appears to be secondary to increased concentrations of phenylalanine and a decrease in the concentrations of other large neutral amino acids, especially methionine and tyrosine, within the central nervous system. This causes a deficiency of the neurotransmitter dopamine, reduced protein synthesis and demyelination. Similar mechanisms appear to be operating when blood phenylalanine concentrations are in the range expected for early continuously treated phenylketonuria. CONCLUSION: The severe brain disease found in phenylketonuria is caused by a raised blood phenylalanine content which increases the brain free phenylalanine and decreases the concentration of other large neutral amino acids. Brain protein synthesis is decreased, myelin turnover is increased and there are abnormalities in amine neurotransmitter systems.

Amino Acids↗
PubMed2000

Urinary oxalate excretion in urolithiasis and nephrocalcinosis.

AIMS: To investigate urinary oxalate excretion in children with urolithiasis and/or nephrocalcinosis and to classify hyperoxaluria (HyOx). METHODS: A total of 106 patients were screened. In those in whom the oxalate: creatinine ratio was increased, 24 hour urinary oxalate excretion was measured. Liver biopsy and/or genomic analysis was performed if primary hyperoxaluria (PH) was suspected. Stool specimens were examined for Oxalobacter formigenes in HyOx not related to PH type 1 or 2 (PH1, PH2) and in controls. RESULTS: A total of 21 patients screened had HyOx (>0.5 mmol/24 h per 1.73 m(2)); they were classified into five groups. Eleven had PH (PH1 in nine and neither PH1 nor PH2 in two). Six had secondary HyOx: two enteric and four dietary. Four could not be classified. Seven patients had concomitant hypercalciuria. Only one of 12 patients was colonised with O formigenes compared to six of 13 controls. CONCLUSIONS: HyOx is an important risk factor for urolithiasis and nephrocalcinosis in children, and can coexist with hypercalciuria. A novel type of PH is proposed. Absence of O formigenes may contribute to HyOx not related to PH1.

Adolescent↗
PubMed1999

Serine 19 of human 6-pyruvoyltetrahydropterin synthase is phosphorylated by cGMP protein kinase II.

6-Pyruvoyltetrahydropterin synthase (PTPS) participates in tetrahydrobiopterin cofactor biosynthesis. We previously identified in a PTPS-deficient patient an inactive PTPS allele with an Arg(16) to Cys codon mutation. Arg(16) is located in the protein surface exposed phosphorylation motif Arg(16)-Arg-Ile-Ser, with Ser(19) as the putative phosphorylation site for serine-threonine protein kinases. Purification of recombinant PTPS-S19A from bacterial cells resulted in an active enzyme (k(cat)/K(m) = 6.4 x 10(3) M(-1) s(-1)), which was similar to wild-type PTPS (k(cat)/K(m) = 4.1 x 10(3) M(-1) s(-1)). In assays with purified enzymes, wild-type but not PTPS-S19A was a specific substrate for the cGMP-dependent protein kinase (cGK) type I and II. Upon expression in COS-1 cells, PTPS-S19A was stable but not phosphorylated and had a reduced activity of approximately 33% in comparison to wild-type PTPS. Extracts from several human cell lines, including brain, contained a kinase that bound to and phosphorylated immobilized wild-type, but not mutant PTPS. Addition of cGMP stimulated phosphotransferase activity 2-fold. Extracts from transfected COS-1 cells overexpressing cGKII stimulated Ser(19) phosphorylation more than 100-fold, but only 4-fold from cGKI overexpressing cells. Moreover, fibroblast extracts from mice lacking cGKII exhibited significantly reduced phosphorylation of PTPS. These results suggest that Ser(19) of human PTPS may be a substrate for cGKII phosphorylation also in vivo, a modification that is essential for normal activity.

Alkaloids↗
PubMed1999

Dominant negative allele (N47D) in a compound heterozygote for a variant of 6-pyruvoyltetrahydropterin synthase deficiency causing transient hyperphenylalaninemia.

Mutations in the 6-pyruvoyltetrahydropterin synthase (PTPS) gene result in persistent hyperphenylalaninemia and severe catecholamine and serotonin deficiencies. We investigated at the DNA level a family with a PTPS-deficient child presenting with an unusual form of transient hyperphenylalaninemia. The patient exhibited compound heterozygosity for the PTPS-mutant alleles N47D and D116G. Transfection studies with single PTPS alleles in COS-1 cells showed that the N47D allele was inactive, while D116G had around 66% of the wild-type activity. Upon co-transfection of two PTPS alleles into COS-1 cells, the N47D allele had a dominant negative effect on both the wild-type PTPS and the D116G mutant with relative reduction to about 20% of control values. Whereas the mother and the father had reduced enzyme activity in red blood cells (34.7% and 51.7%, respectively) and skin fibroblasts (2.8% and 15.4%, respectively), the clinically normal patient had in these cells activities at the detection limits, although PTPS-cross-reactive material was present in the fibroblasts. The specifically low PTPS activity in the mother's cells corroborated the evidence of a dominant negative effect of the maternal N47D allele on wild-type PTPS.

Animals↗