Argininosuccinic Aciduria Research Articles

P17.13 A case of argininosuccinic aciduria associated with high serum creatinine phosphokinase levels

P17.13 A case of argininosuccinic aciduria associated with high serum creatinine phosphokinase levels

Argininosuccinate lyase deficiency—Argininosuccinic aciduria and beyond

The urea cycle consists of six consecutive enzymatic reactions that convert waste nitrogen into urea. Deficiencies of any of these enzymes of the cycle result in urea cycle disorders (UCD), a group of inborn errors of hepatic metabolism that often result in life threatening hyperammonemia. Argininosuccinate lyase (ASL) is a cytosolic enzyme which catalyzes the fourth reaction in the cycle and the first degradative step, that is, the breakdown of argininosuccinic acid to arginine and fumarate. Deficiency of ASL results in an accumulation of argininosuccinic acid in tissues, and excretion of argininosuccinic acid in urine leading to the condition argininosuccinic aciduria (ASA). ASA is an autosomal recessive disorder and is the second most common UCD. In addition to the accumulation of argininosuccinic acid, ASL deficiency results in decreased synthesis of arginine, a feature common to all UCDs except argininemia. Arginine is not only the precursor for the synthesis of urea and ornithine as part of the urea cycle but it is also the substrate for the synthesis of nitric oxide, polyamines, proline, glutamate, creatine, and agmatine. Hence, while ASL is the only enzyme in the body able to generate arginine, at least four enzymes use arginine as substrate: arginine decarboxylase, arginase, nitric oxide synthetase (NOS) and arginine/glycine aminotransferase. In the liver, the main function of ASL is ureagenesis, and hence, there is no net synthesis of arginine. In contrast, in most other tissues, its role is to generate arginine that is designated for the specific cell's needs. While patients with ASA share the acute clinical phenotype of hyperammonemia, encephalopathy, and respiratory alkalosis common to other UCD, they also present with unique chronic complications most probably caused by a combination of tissue specific deficiency of arginine and/or elevation of argininosuccinic acid. This review article summarizes the clinical characterization, biochemical, enzymatic, and molecular features of this disorder. Current treatment, prenatal diagnosis, diagnosis through the newborn screening as well as hypothesis driven future treatment modalities are discussed.

The First Neonatal Case of Neonatal Argininosuccinic Aciduria in Korea

Argininosuccinic aciduria (ASAuria) is a rare autosomal recessive urea cycle disorder. Neonatal presentation of ASAuria is the most common form. It is characterized by lethargy, feeding intolerance, decreased consciousness, and coma after 24 to 72 hours of birth. We describe a rare case of ASAuria in a female neonate who presented with severe hyperammonemia, a typical characteristic of urea cycle disorders. This patient’s diagnosis was confirmed by biochemical analyses, and we found that the patient had a point mutation of the argininosuccinate lyase gene, which was homozygous for a novel 556C>T substitution. We have never seen the neonatal form of ASAuria in Korea. Therefore, this is the first report of neonatal onset ASAuria in Korea.

677. A Combination of Pharmacological and Liver-Directed Gene Therapy Results in Long-Term Phenotypic Correction of a Mouse Model of Argininosuccinic Aciduria

677. A Combination of Pharmacological and Liver-Directed Gene Therapy Results in Long-Term Phenotypic Correction of a Mouse Model of Argininosuccinic Aciduria

Novel mutations underlying argininosuccinic aciduria in Saudi Arabia

BackgroundArgininosuccinic aciduria (ASAuria) is an autosomal recessive disorder of the urea cycle relatively common in Saudi Arabia as a consequence of extensive consanguinity. It is the most common urea cycle disorder identified in the Saudi population, which therefore prioritizes the need to delineate the underlying molecular defects leading to disease.FindingsWe utilized Whole Genome Amplification (WGA), PCR and direct sequencing to identify mutations underlying ASAuria cases diagnosed by our institution. A missense mutation that accounts for 50% of Saudi ASAuria patients was recently reported by our laboratory. In this study we report a further six novel mutations (and one previously reported) found in Saudi patients with ASAuria. The novel four missense, one nonsense and one splice-site mutation were confirmed by their absence in >300 chromosomes from the normal population. Pathogenicity of the novel splice-site mutation was also confirmed using reverse transcriptase-PCR analysis. Cross species amino acid conservation at the substituted residues described were observed in some but not all instances.ConclusionsTogether, the eight mutations described by our laboratory, encompass >90% of ASAuria patients in Saudi Arabia and add to about 45 other ASAuria mutations reported worldwide.

Long-term outcome of patients with argininosuccinate lyase deficiency diagnosed by newborn screening in Austria

Twenty-three patients with late onset argininosuccinate lyase deficiency (ASLD) were identified during a 27-year period of newborn screening in Austria (1:95,600, 95% CI=1:68,036–1:162,531). One additional patient was identified outside the newborn screening with neonatal hyperammonemia. Long-term outcome data were available in 17 patients (median age 13years) ascertained by newborn screening. Patients were treated with protein restricted diet and oral arginine supplementation during infancy and childhood. IQ was average/above average in 11 (65%), low average in 5 (29%), and in the mild intellectual disability range in 1 (6%) patients. Four patients had an abnormal EEG without evidence of clinical seizures and three had abnormal liver function tests and/or evidence of hepatic steatosis. Plasma citrulline levels were elevated in four patients. Plasma ammonia levels were within normal range prior and after a protein load in all patients. Seven different mutations were identified in the 16 alleles investigated. Four mutations were novel (p.E189G, p.R168C, p.R126P, and p.D423H). All mutations were associated with low argininosuccinate lyase activities (0–15%) in red blood cells. Newborn screening might be beneficial in the prevention of chronic neurologic and intellectual sequelae in late onset ASLD, but a proportion of benign variants might have contributed to the overall favorable outcome as well.

Clinical and biochemical characteristics of patients with urea cycle disorders in a developing country

Objectives To report the clinical and laboratory characteristics of urea cycle disorder (UCD) patients at a tertiary care center in a developing country. Design and methods Retrospective study of clinical and laboratory data of UCD patients. Results Thirty-seven UCD patients were studied, 31 symptomatic (high risk) patients (15 neonatal onset, 16 late onset) and 6 with positive neonatal screening. Argininosuccinate synthetase deficiency was the most frequent disease (17/37, 46%), followed by ornithine transcarbamylase (10/37, 27%), arginase (7/37, 19%), and argininosuccinate lyase (3/37, 8%) deficiencies. Mortality of symptomatic patients was 38% (10/26), neonatal onset had the worst outcome, with 50% of survival. Conclusions In Mexico, the mortality of the UCD patients is higher than those reported in other countries, and neurological sequels are frequent and severe. It is essential to implement practice guidelines for the professional management of these patients.

Functional Complementation in Yeast Allows Molecular Characterization of Missense Argininosuccinate Lyase Mutations

Deficiency of argininosuccinate lyase (ASL) causes argininosuccinic aciduria, an urea cycle defect that may present with a severe neonatal onset form or with a late onset phenotype. To date phenotype-genotype correlations are still not clear because biochemical assays of ASL activity correlate poorly with clinical severity in patients. We employed a yeast-based functional complementation assay to assess the pathogenicity of 12 missense ASL mutations, to establish genotype-phenotype correlations, and to screen for intragenic complementation. Rather than determining ASL enzyme activity directly, we have measured the growth rate in arginine-free medium of a yeast ASL(null) strain transformed with individual mutant ASL alleles. Individual haploid strains were also mated to obtain diploid, "compound heterozygous" yeast. We show that the late onset phenotypes arise in patients because they harbor individual alleles retaining high residual enzymatic activity or because of intragenic complementation among different mutated alleles. In these cases complementation occurs because in the hybrid tetrameric enzyme at least one active site without mutations can be formed or because the differently mutated alleles can stabilize each other, resulting in partial recovery of enzymatic activity. Functional complementation in yeast is simple and reproducible and allows the analysis of large numbers of mutant alleles. Moreover, it can be easily adapted for the analysis of mutations in other genes involved in urea cycle disorders.

Experience with the treatment of argininosuccinic aciduria during pregnancy

We present the details of the management and the outcome of a pregnancy of a woman affected with argininosuccinic aciduria. Management with a closely monitored, protein-restricted diet, supplemented with L-arginine, resulted in the birth of a healthy infant boy and an uneventful perinatal course for the mother.

Argininosuccinate lyase deficiency: Longterm outcome of 13 patients detected by newborn screening

Argininosuccinate lyase deficiency is a urea cycle disorder which can present in the neonatal period with hyperammonemic encephalopathy, or later in childhood with episodic vomiting, growth and developmental delay. Abnormal hair, hepatomegaly, and hepatic fibrosis are unique features of this disorder. Twelve patients with argininosuccinate lyase deficiency were ascertained between 4 and 6 weeks of age by urine amino acid screening. One infant in a previously identified family was diagnosed shortly after birth. Diagnosis was confirmed by enzyme assay in red blood cells and/or skin fibroblasts. At the time of last follow-up, patients had been followed for 13–33 years. All patients were asymptomatic at detection, 7 had slightly increased blood ammonia, and all were initially treated with low-protein diet. Utilization of 14C-citrulline by intact skin fibroblasts measured by 14C incorporation into macromolecules was 74–135% of the control mean for 7 of the 8 patients studied. Nine patients had normal development, 4 had learning disability, 6 had EEG abnormalities, 3 had seizure disorder. None had any episodes of hyperammonemic coma. None had hepatomegaly. Patients detected by screening had higher enzyme activity measured by the 14C-citrulline incorporation assay than comparison groups of patients with neonatal-onset and with late-onset detected by clinical disease. The ability to utilize 14C-citrulline by intact fibroblasts seems to correlate with clinical outcome and may have prognostic value. It is likely that early diagnosis and treatment contributed to the relatively mild clinical course of the study group.

Systemic hypertension in two patients with ASL deficiency: A result of nitric oxide deficiency?

Argininosuccinic aciduria (ASA) is an inborn error of ureagenesis which if untreated leads to hyperammonemia, accumulation of argininosuccinic acid and arginine depletion. The presence of high blood pressure in patients with ASA has been reported so far as transient in one newborn. We describe the first two patients, one child and one young adult, with ASA and persistent systemic hypertension. Extensive evaluation of both patients excluded secondary causes of systemic hypertension. The intriguing link between nitric oxide (NO) production and hypertension lead us to hypothesize that the deficiency of endogenously synthesized arginine caused by ASL deficiency is responsible for the increased blood pressure.

173. Phenotypic Correction of the Hypomorphic Mouse Model of Argininosuccinate Lyase Deficiency Using Small Molecules and Gene Therapy

173. Phenotypic Correction of the Hypomorphic Mouse Model of Argininosuccinate Lyase Deficiency Using Small Molecules and Gene Therapy

Treatment of a Newborn with Urea-Cycle-Disorder and Cerebral Edema with Venovenous Hemodiafiltration and Therapeutic Hypothermia

We report about a term newborn with urea-cycle disorder with severe cerebral edema in which the pharmacological treatment was combined with venovenous hemodiafiltration (VVHDF) and therapeutic hypothermia. A 50h old boy was admitted at a NICU in an external hospital because of convulsions and respiratory failure. Initial metabolic workup showed ammonia 2320µmol/l and the boy was transferred to our hospital. Initial examination showed a ventilated newborn with hepatomegalia and severe hypotension and ammonia concentrations of 2391µmol/l under treatment with Arginin-HCL and Na-Benzoat. Cranial ultrasound (CUS) showed a cerebral edema with systolic peaks and a pulsatility index (PI) of 3.0. After placing of a dual lumen catheter in the right jugularian vein VVHDF was started. In addition neuroprotection was performed by cooling the boy to a rectal temperature of 33°C for the first 24h using CritiCool cooling therapy system. Then the boy was rewarmed stepwise to 36°C over the next 48h. Ammonia concentration was decreased during the first 3h to 830.4µmol/l by VVHDF and CUS showed a significant improvement of the cerebral blood flow. VVHDF was stopped 3h later at ammonia 224.3µmol/l. There was no rebound of hyperammonemia and CUS showed regular findings. The metabolic investigation revealed an Argininosuccinate lyase deficiency. After Extubation at day 10, the boy was discharged at day 38. The 2 months follow up showed an adequate neurological development despite the classic signs of metabolic stroke in MRI. Conclusion: Life-threatening cerebral edema in newborns with inborn urea-cycle defects can be treated effectively by the combination of VVHDF with therapeutic hypothermia.

Evaluation of endogenous nitric oxide synthesis in congenital urea cycle enzyme defects

Nitric oxide (NO) is synthesized from arginine and O 2 by nitric oxide synthase (NOS). Citrulline, which is formed as a by-product of the NOS reaction, can be recycled to arginine by the 2 enzymes acting in the urea cycle: argininosuccinate synthetase (ASS) and argininosuccinate lyase (ASL). Although the complete urea cycle is expressed only in the liver, ASS and ASL are expressed in other organs including the kidney and vascular endothelium. To examine possible alterations of the NO pathway in urea cycle defects, we measured plasma concentrations of arginine and citrulline and serum concentrations of nitrite/nitrate (NOx −, stable NO metabolites) and asymmetric dimethylarginine (ADMA, an endogenous NOS inhibitor) in patients with congenital urea cycle disorders of 3 types: ornithine transcarbamylase (OTC) deficiency, ASS deficiency, and ASL deficiency. All were receiving oral arginine replacement at the time of this study. The same parameters were also measured in healthy subjects, who participated as controls. The OTC-deficient patients had significantly high NOx − and nonsignificantly high ADMA concentrations. Their NOx − was significantly positively correlated with arginine. The ASS-deficient patients had significantly low NOx − and significantly high ADMA concentrations. The ASL-deficient patients had normal NOx − and nonsignificantly high ADMA concentrations. In ASS-deficient and ASL-deficient patients, the NOx − was significantly inversely correlated with citrulline. These results suggest that NO synthesis is enhanced in OTC-deficient patients while receiving arginine but that NO synthesis remains low in ASS-deficient patients despite receiving arginine. They also suggest that endogenous NO synthesis is negatively affected by citrulline and ADMA in ASS-deficient and ASL-deficient patients. Although the molecular mechanisms remain poorly understood, we infer that the NO pathway might play a role in the pathophysiology related to congenital urea cycle disorders.

Bloodspot acylcarnitine and amino acid analysis in cord blood samples: efficacy and reference data from a large cohort study

In order to test the feasibility of cord blood screening for inherited metabolic disease, a two-year cohort study of births in six obstetric units from five towns in the north of England was undertaken. These towns have a high prevalence of consanguineous marriages, largely among the immigrant Asian community. The purpose of the study was to determine whether early detection of metabolic disease was possible and whether early intervention would improve prognosis. Following parental consent, cord blood samples were collected at birth and analysed for acylcarnitine and amino acid profiles by tandem mass spectrometry in one of two laboratories. One laboratory used butylated derivatives, the other used underivatized samples. The same laboratories performed routine blood spot neonatal screening at 5-7 days of age on these babies. Patients with positive results were investigated and treated by a metabolic paediatrician as soon as possible. 24,983 births were examined. 12,952 samples were analysed as butyl derivatives, 12,031 samples were analysed underivatized. The following disorders were detected: medium-chain acyl-CoA dehydrogenase (MCAD) deficiency (1 case), 3-methylcrotonyl-CoA carboxylase (MCC) deficiency (2 cases), maternal carnitine transporter defect (2 cases), maternal MCC (1 case). The following disorders were diagnosed subsequently but were not detected by the cord blood screening: phenylketonuria (PKU) (1 case), maple syrup urine disease (MSUD) (2 cases), argininosuccinic aciduria (1 case), methylmalonic acidaemia (MMA) (1 case), glutaric aciduria type 2 (1 case), MCAD deficiency (2 cases), 3-hydroxy-3-methylglutaryl-CoA lyase deficiency (1 case). Comprehensive reference data for all analytes by both methods were obtained. Cord blood testing is of limited value in detecting inherited metabolic disease. The metabolites associated with most disorders examined were not elevated in cord blood. Some maternal disorders, carnitine transporter defect and 3-methlycrotonyl-CoA carboxylase deficiency, are detected. These remain of uncertain clinical significance. Comprehensive reference data have been obtained that will facilitate future interpretation of studies in cord blood.

Population screening in a Druze community: the challenge and the reward

PurposeThe Druze community is characterized by consanguinity and endogamy, and by reluctance to genetic testing and technological interventions for the prevention of birth defects. Multiple patients with four rare and severe inborn errors of metabolism cerebrotendinous xanthomatosis, prolidase deficiency, argininosuccinate lyase deficiency, and carbamyl phosphate synthetase I deficiency were identified in an isolated Druze village in northern Israel. The aims of this study were to identify couples at risk for four inherited diseases, and to prevent birth defects in a community presenting religious and cultural obstacles to genetic testing. MethodsA genetic screening and counseling program in a high-risk community. ResultsThe 1425 residents who attended group genetic counseling sessions between 2003 and 2007 consented to genetic testing. We identified 217 carriers for either one or two disease causing mutations. High carrier frequencies for cerebrotendinous xanthomatosis, prolidase deficiency, argininosuccinate lyase deficiency, and carbamyl phosphate synthetase I deficiency were identified as 1:11, 1:21, 1:41, and 1:95, respectively. Fifty-eight percent (125) of the carriers' spouses agreed to genetic counseling and testing. Ten couples at risk for affected offspring were identified and offered prenatal genetic counseling and diagnosis. ConclusionsThe genetic screening program, the first of its kind reported in a Druze community, was well received. We expect this program to increase awareness of genetic counseling, to contribute to disease prevention, and to serve as a model for other isolated communities.

Hereditary urea cycle diseases in Finland

To estimate the incidence of urea cycle diseases (UCDs) in Finland and determine the course of the various disorders as well as the outcome. The original data were collected in the years 1998-2001. The diagnoses made after 2001, as well as the current status of the patients, were updated by surveys in the spring of 2007. We found a total of 55 cases of UCDs in Finland by 2007: 30 cases of ornithine transcarbamylase (OTC) deficiency, 20 of argininosuccinate lyase (ASL) deficiency, 3 of carbamyl phosphate synthetase (CPS-I) deficiency, 1 of type 1 citrullinaemia and 1 of argininaemia. The estimated total incidence of UCDs was 1:39 000. The incidences of individual disorders were: OTC deficiency 1:62 000, ASL deficiency 1:144 000, CPS deficiency 1:539 000 and citrullinaemia 1:1 616 000. Eighteen (33%) of the patients with a diagnosis of UCD have died, most during their first hyperammonaemic crisis. One patient with OTC deficiency has had a liver transplant. Neurological symptoms of varying severity are common among these patients, particularly those with ASL deficiency. The first survey on the incidence of UCDs in Finland shows some differences in the occurrence rates compared to other countries. Hyperammonaemia, and the neurological symptoms caused by it, can be avoided in most patients with late-onset UCDs with a standard treatment. However, in patients with ASL deficiency, the development of neurological symptoms seems to be inevitable in spite of careful treatment and avoidance of hyperammonaemia.

Cross-sectional multicenter study of patients with urea cycle disorders in the United States

Inherited urea cycle disorders comprise eight disorders (UCD), each caused by a deficiency of one of the proteins that is essential for ureagenesis. We report on a cross-sectional investigation to determine clinical and laboratory characteristics of patients with UCD in the United States. The data used for the analysis was collected at the time of enrollment of individuals with inherited UCD into a longitudinal observation study. The study has been conducted by the Urea Cycle Disorders Consortium within the Rare Diseases Clinical Research Network (RDCRN) funded by the National Institutes of Health. One-hundred eighty-three patients were enrolled into the study. Ornithine transcarbamylase (OTC) deficiency was the most frequent disorder (55%), followed by argininosuccinic aciduria (16%) and citrullinemia (14%). Seventy-nine percent of the participants were white (16% Latinos), and 6% were African American. Intellectual and developmental disabilities were reported in 39% with learning disabilities (35%) and half had abnormal neurological examination. Sixty-three percent were on a protein restricted diet, 37% were on Na-phenylbutyrate and 5% were on Na-benzoate. Forty-five percent of OTC deficient patients were on l-citrulline, while most patients with citrullinemia (58%) and argininosuccinic aciduria (79%) were on l-arginine. Plasma levels of branched-chain amino acids were reduced in patients treated with ammonia scavenger drugs. Plasma glutamine levels were higher in proximal UCD and in neonatal type disease. The RDCRN allows comprehensive analyses of rare inherited UCD, their frequencies and current medical practices.

Living Related Liver Transplant in a Patient With Argininosuccinic Aciduria and Cirrhosis: Metabolic Follow‐up

Living Related Liver Transplant in a Patient With Argininosuccinic Aciduria and Cirrhosis: Metabolic Follow‐up

Usefulness of Magnetic Resonance Spectroscopy in Urea Cycle Disorders

Late-onset urea cycle disorders are characterized by chronic encephalopathy and a risk of hyperammonemic crises triggered by environmental stressors. Reported here is the case of a 30-year-old woman with chronic encephalopathy due to argininosuccinate lyase deficiency. Cerebral proton magnetic resonance spectroscopy showed brain creatine deficiency and its normalization during treatment. These findings are in keeping with recent reports suggesting that creatine deficiency is involved in the neurological dysfunction of urea cycle disorders and demonstrate the usefulness of magnetic resonance spectroscopy in the diagnosis and follow-up of urea cycle disorders.