Analysis of pyrimidine synthesis "de novo" intermediates in urine and dried urine filter- paper strips with HPLC-electrospray tandem mass spectrometry. (1/21)

BACKGROUND: The concentrations of the pyrimidine "de novo" metabolites and their degradation products in urine are useful indicators for the diagnosis of an inborn error of the pyrimidine de novo pathway or a urea-cycle defect. Until now, no procedure was available that allowed the analysis of all of these metabolites in a single analytical run. We describe a rapid, specific method to measure these metabolites by HPLC-tandem mass spectrometry. METHODS: Urine or urine-soaked filter-paper strips were used to measure N-carbamyl-aspartate, dihydroorotate, orotate, orotidine, uridine, and uracil. Reversed-phase HPLC was combined with electrospray ionization tandem mass spectrometry, and detection was performed by multiple-reaction monitoring. Stable-isotope-labeled reference compounds were used as internal standards. RESULTS: All pyrimidine de novo metabolites and their degradation products were measured within a single analytical run of 14 min with lower limits of detection of 0.4-3 micromol/L. The intra- and interassay variation for urine with added compounds was 1.2-5% for urines and 2-9% for filter-paper extracts of the urines. Recoveries of the added metabolites were 97-106% for urine samples and 97-115% for filter-paper extracts of the urines. Analysis of urine samples from patients with a urea-cycle defect or pyrimidine degradation defect showed an aberrant metabolic profile when compared with controls. CONCLUSION: HPLC with electrospray ionization tandem mass spectrometry allows rapid testing for disorders affecting the pyrimidine de novo pathway. The use of filter-paper strips could facilitate collection, transport, and storage of urine samples.  (+info)

Clinical consequences of urea cycle enzyme deficiencies and potential links to arginine and nitric oxide metabolism. (2/21)

Urea cycle disorders (UCD) are human conditions caused by the dysregulation of nitrogen transfer from ammonia nitrogen into urea. The biochemistry and the genetics of these disorders were well elucidated. Earlier diagnosis and improved treatments led to an emerging, longer-lived cohort of patients. The natural history of some of these disorders began to point to pathophysiological processes that may be unrelated to the primary cause of acute morbidity and mortality, i.e., hyperammonemia. Carbamyl phosphate synthetase I single nucleotide polymorphisms may be associated with altered vascular resistance that becomes clinically relevant when specific environmental stressors are present. Patients with argininosuccinic aciduria due to a deficiency of argininosuccinic acid lyase are uniquely prone to chronic hepatitis, potentially leading to cirrhosis. Moreover, our recent observations suggest that there may be an increased prevalence of essential hypertension. In contrast, hyperargininemia found in patients with arginase 1 deficiency is associated with pyramidal tract findings and spasticity, without significant hyperammonemia. An intriguing potential pathophysiological link is the dysregulation of intracellular arginine availability and its potential effect on nitric oxide (NO) metabolism. By combining detailed natural history studies with the development of tissue-specific null mouse models for urea cycle enzymes and measurement of nitrogen flux through the cycle to urea and NO in UCD patients, we may begin to dissect the contribution of different sources of arginine to NO production and the consequences on both rare genetic and common multifactorial diseases.  (+info)

Neonatal argininosuccinic aciduria with normal brain and kidney but absent liver argininosuccinate lyase activity. (3/21)

An infant is described who died at 6 days of age with hyperammonemia and argininosuccinic acid in the urine. Argininosuccinic acid lyase (AL) was absent in liver, decreased in red blood cells, but normal in brain and kidney. The instability of AL in frozen stored tissues accounts for previous reports of deficient AL activity in the brain and kidney of neonates with this disease. The variation of AL activity in the tissues of this patient demonstrates that more than one gene locus either codes for the structure of this enzyme or regulates its biosynthesis in different organs.  (+info)

Contrasting features of urea cycle disorders in human patients and knockout mouse models. (4/21)

The urea cycle exists for the removal of excess nitrogen from the body. Six separate enzymes comprise the urea cycle, and a deficiency in any one of them causes a urea cycle disorder (UCD) in humans. Arginase is the only urea cycle enzyme with an alternate isoform, though no known human disorder currently exists due to a deficiency in the second isoform. While all of the UCDs usually present with hyperammonemia in the first few days to months of life, most disorders are distinguished by a characteristic profile of plasma amino acid alterations that can be utilized for diagnosis. While enzyme assay is possible, an analysis of the underlying mutation is preferable for an accurate diagnosis. Mouse models for each of the urea cycle disorders exist (with the exception of NAGS deficiency), and for almost all of them, their clinical and biochemical phenotypes rather closely resemble the phenotypes seen in human patients. Consequently, all of the current mouse models are highly useful for future research into novel pharmacological and dietary treatments and gene therapy protocols for the management of urea cycle disorders.  (+info)

Systemic hypertension in two patients with ASL deficiency: a result of nitric oxide deficiency? (5/21)

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Argininosuccinate lyase deficiency: longterm outcome of 13 patients detected by newborn screening. (6/21)

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Argininosuccinate lyase deficiency-argininosuccinic aciduria and beyond. (7/21)

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Argininosuccinic aciduria: clinical and biochemical phenotype findings in Malaysian children. (8/21)

Argininosuccinic aciduria is an inborn error of the urea cycle caused by deficiency of argininosuccinate lyase (ASL). ASL-deficient patients present with progressive intoxication due to accumulation of ammonia in the body. Early diagnosis and treatment of hyperammonemia are necessary to improve survival and prevent long-term handicap. Two clinical phenotypes have been recognized--neonatal acute and milder late-onset form. We investigated patients with hyperammonemia by a stepwise approach in which quantitative amino acids analysis was the core diagnostic procedure. Here, we describe the clinical phenotypes and biochemical characteristics in diagnosing this group of patients. We have identified 13 patients with argininosuccinic aciduria from 2003 till 2009. Ten patients who presented with acute neonatal hyperammonemic encephalopathy had markedly elevated blood ammonia (> 430 micromol/L) within the first few days of life. Three patients with late-onset disease had more subtle clinical presentations and they developed hyperammonemia only during the acute catabolic state at two to twelve months of age. Their blood ammonia was mild to moderately elevated (> 75-265 micromol/L). The diagnosis was confirmed by detection of excessive levels of argininosuccinate in the urine and/or plasma. They also have moderately increased levels of citrulline and, low levels of arginine and ornithine in their plasma. Two patients succumbed to the disease. To date, eleven patients remained well on a dietary protein restriction, oral ammonia scavenging drugs and arginine supplementation. The majority of them have a reasonable good neurological outcome.  (+info)

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