Spastic gait, intellectual disability and seizures due to a rare mutation causing hyperargininemia.

Hyperargininemia is an autosomal recessive disorder caused by a defect in the arginase I enzyme. We present a case of a 20-year-old male with severe spastic gait, intellectual disability and seizures. Metabolic tests revealed high levels of arginine in blood serum. Hyperargininemia was attributed to a likely pathogenic rare mutation of ARG1 gene [Chr6: g131905002_131905002 G>A (p.Arg308Gln) homozygous] detected in Whole Exome Sequencing resulting in deficiency in arginase I enzyme. Following the diagnosis, the patient has been treated with low protein diet, aminoacid and vitamin supplements. The accumulation of arginine, may contribute to the pathogenesis of severe neurological manifestations, however, low protein intake diet may lead to a favorable outcome. Therefore, clinicians should screen for hyperargininemia in early childhood in case of strong clinical suspicion.

Clinical effect and safety profile of pegzilarginase in patients with arginase 1 deficiency.

Hyperargininemia in patients with arginase 1 deficiency (ARG1-D) is considered a key driver of disease manifestations, including spasticity, developmental delay, and seizures. Pegzilarginase (AEB1102) is an investigational enzyme therapy which is being developed as a novel arginine lowering approach. We report the safety and efficacy of intravenously (IV) administered pegzilarginase in pediatric and adult ARG1-D patients (n = 16) from a Phase 1/2 study (101A) and the first 12 weeks of an open-label extension study (102A). Substantial disease burden at baseline included lower-limb spasticity, developmental delay, and previous hyperammonemic episodes in 75%, 56%, and 44% of patients, respectively. Baseline plasma arginine (pArg) was elevated (median 389 µM, range 238-566) on standard disease management. Once weekly repeat dosing resulted in a median decrease of pArg of 277 µM after 20 cumulative doses (n = 14) with pArg in the normal range (40 to 115 µM) in 50% of patients at 168 hours post dose (mean pegzilarginase dose 0.10 mg/kg). Lowering pArg was accompanied by improvements in one or more key mobility assessments (6MWT, GMFM-D & E) in 79% of patients. In 101A, seven hypersensitivity reactions occurred in four patients (out of 162 infusions administered). Other common treatment-related adverse events (AEs) included vomiting, hyperammonemia, pruritus, and abdominal pain. Treatment-related serious AEs that occurred in five patients were all observed in 101A. Pegzilarginase was effective in lowering pArg levels with an accompanying clinical response in patients with ARG1-D. The improvements with pegzilarginase occurred in patients receiving standard treatment approaches, which suggests that pegzilarginase could offer benefit over existing disease management.

Sodium phenylbutyrate improved the clinical state in an adult patient with arginase 1 deficiency.

An adult female patient was diagnosed with arginase 1 deficiency (ARG1-D) at 4 years of age, and had been managed with protein restriction combined with sodium benzoate therapy. Though the treatment was successful in ameliorating hyperammonemia, hyperargininemia persisted. After being under control with a strict restriction of dietary protein, severe fall of serum albumin levels appeared and her condition became strikingly worsened. However, after sodium phenylbutyrate (NaPB) therapy was initiated, the clinical condition and metabolic stability was greatly improved. Current management of ARG1-D is aimed at lowering plasma arginine levels. The nitrogen scavengers, such as NaPB can excrete the waste nitrogen not through the urea cycle but via the alternative pathway. The removal of nitrogen via alternative pathway lowers the flux of arginine in the urea cycle. Thereby, the clinical complications due to insufficient amount of protein intake can be prevented. Thus, NaPB therapy can be expected as a useful therapeutic option, particularly in patients with ARG1-D.

Leveraging Rational Protein Engineering to Improve mRNA Therapeutics.

Messenger RNA (mRNA) is a promising new class of therapeutics that has potential for treatment of diseases in fields such as immunology, oncology, vaccines, and inborn errors of metabolism. mRNA therapy has several advantages over DNA-based gene therapy, including the lack of the need for nuclear import and transcription, as well as limited possibility of genomic integration. One drawback of mRNA therapy, especially in cases such as metabolic disorders where repeated dosing will be necessary, is the relatively short in vivo half-life of mRNA (∼6-12 h). We hypothesize that protein engineering designed to improve translation, yielding longer-lasting protein, or modifications that would increase enzymatic activity would be helpful in alleviating this issue. In this study, we present two examples where sequence engineering improved the expression and duration, as well as enzymatic activity of target proteins in vitro. We then confirmed these findings in wild-type mice. This work shows that rational engineering of proteins can lead to improved therapies in vivo.

Biochemical markers and neuropsychological functioning in distal urea cycle disorders.

Urea cycle disorders often present as devastating metabolic conditions, resulting in high mortality and significant neuropsychological damage, despite treatment. The Urea Cycle Disorders Longitudinal Study is a natural history study that collects data from regular clinical follow-up and neuropsychological testing. This report examines links between biochemical markers (ammonia, glutamine, arginine, citrulline) and primary neuropsychological endpoints in three distal disorders, argininosuccinic acid synthetase deficiency (ASD or citrullinemia type I), argininosuccinic acid lyase deficiency (ASA or ALD), and arginase deficiency (ARGD). Laboratory results and test scores from neuropsychological evaluations were assessed in 145 study participants, ages 3 years and older, with ASD (n = 64), ASA (n = 65) and ARGD (n = 16). Mean full scale IQ was below the population mean of 100 ± 15 for all groups: (ASD = 79 ± 24; ASA = 71 ± 21; ARGD = 65 ± 19). The greatest deficits were noted in visual performance and motor skills for all groups. While ammonia levels remain prominent as prognostic biomarkers, other biomarkers may be equally valuable as correlates of neuropsychological functioning. Cumulative exposure to the biomarkers included in the study proved to be highly sensitive indicators of neuropsychological outcomes, even when below the cut-off levels generally considered toxic. Blood levels of biomarkers obtained on the day of neuropsychological evaluations were not correlated with measures of functioning for any disorder in any domain. The importance of cumulative exposure supports early identification and confirms the need for well-controlled management of all biochemical abnormalities (and not just ammonia) that occur in urea cycle disorders.

Newborn screening for hyperargininemia due to arginase 1 deficiency.

Hyperargininemia caused by Arginase 1 deficiency is a rare disorder of the urea cycle that can be diagnosed by elevation of arginine in newborn screening blood spots when analyzed by tandem mass spectrometry. Hyperargininemia is currently included as a secondary target on the U.S. Recommended Uniform Screening Panel, which directly influences state-based newborn screening. Because of the apparent low disease frequency and lack of case detection and treatment data, detailed attention has not been given to a model newborn screening algorithm including appropriate analytical cutoff values for disease indicators. In this paper we assess the frequency of hyperargininemia in the U.S. identified by newborn screening to date and document the current status and variability of hyperargininemia newborn screening across U.S. newborn screening programs. We also review other data that support improved screening efficacy by utilizing the arginine/ornithine ratio and other amino acid ratios as discriminators in the screening algorithm. Analysis of archived California screening data showed that an arginine cutoff of 50µM combined with an arginine/ornithine ratio of 1.4 would have resulted in a recall rate of 0.01%. Using an arginine cutoff of 60µM and an arginine/(phenylalanine x leucine) ratio of 1.4, reportedly used in one screening program, or the R4S Tool Runner, would have resulted in a recall rate of <0.005%. All 9 diagnosed patients would have been found for either protocol. Thus, use of appropriate ratios as part of the screening algorithm has the potential to increase both screening sensitivity and specificity. Improved newborn screening effectiveness should lead to better case detection and more rapid treatment to lower plasma arginine levels hence improving long term outcome of individuals with hyperargininemia.

Rescue of the Functional Alterations of Motor Cortical Circuits in Arginase Deficiency by Neonatal Gene Therapy.

UNLABELLED: Arginase 1 deficiency is a urea cycle disorder associated with hyperargininemia, spastic diplegia, loss of ambulation, intellectual disability, and seizures. To gain insight on how loss of arginase expression affects the excitability and synaptic connectivity of the cortical neurons in the developing brain, we used anatomical, ultrastructural, and electrophysiological techniques to determine how single-copy and double-copy arginase deletion affects cortical circuits in mice. We find that the loss of arginase 1 expression results in decreased dendritic complexity, decreased excitatory and inhibitory synapse numbers, decreased intrinsic excitability, and altered synaptic transmission in layer 5 motor cortical neurons. Hepatic arginase 1 gene therapy using adeno-associated virus rescued nearly all these abnormalities when administered to neonatal homozygous knock-out animals. Therefore, gene therapeutic strategies can reverse physiological and anatomical markers of arginase 1 deficiency and therefore may be of therapeutic benefit for the neurological disabilities in this syndrome. SIGNIFICANCE STATEMENT: These studies are one of the few investigations to try to understand the underlying neurological dysfunction that occurs in urea cycle disorders and the only to examine arginase deficiency. We have demonstrated by multiple modalities that, in murine layer 5 cortical neurons, a gradation of abnormalities exists based on the functional copy number of arginase: intrinsic excitability is altered, there is decreased density in asymmetrical and perisomatic synapses, and analysis of the dendritic complexity is lowest in the homozygous knock-out. With neonatal administration of adeno-associated virus expressing arginase, there is near-total recovery of the abnormalities in neurons and cortical circuits, supporting the concept that neonatal gene therapy may prevent the functional abnormalities that occur in arginase deficiency.

Human recombinant arginase enzyme reduces plasma arginine in mouse models of arginase deficiency.

Arginase deficiency is caused by deficiency of arginase 1 (ARG1), a urea cycle enzyme that converts arginine to ornithine. Clinical features of arginase deficiency include elevated plasma arginine levels, spastic diplegia, intellectual disability, seizures and growth deficiency. Unlike other urea cycle disorders, recurrent hyperammonemia is typically less severe in this disorder. Normalization of plasma arginine levels is the consensus treatment goal, because elevations of arginine and its metabolites are suspected to contribute to the neurologic features. Using data from patients enrolled in a natural history study conducted by the Urea Cycle Disorders Consortium, we found that 97% of plasma arginine levels in subjects with arginase deficiency were above the normal range despite conventional treatment. Recently, arginine-degrading enzymes have been used to deplete arginine as a therapeutic strategy in cancer. We tested whether one of these enzymes, a pegylated human recombinant arginase 1 (AEB1102), reduces plasma arginine in murine models of arginase deficiency. In neonatal and adult mice with arginase deficiency, AEB1102 reduced the plasma arginine after single and repeated doses. However, survival did not improve likely, because this pegylated enzyme does not enter hepatocytes and does not improve hyperammonemia that accounts for lethality. Although murine models required dosing every 48 h, studies in cynomolgus monkeys indicate that less frequent dosing may be possible in patients. Given that elevated plasma arginine rather than hyperammonemia is the major treatment challenge, we propose that AEB1102 may have therapeutic potential as an arginine-reducing agent in patients with arginase deficiency.

Minimal ureagenesis is necessary for survival in the murine model of hyperargininemia treated by AAV-based gene therapy.

Hyperammonemia is less severe in arginase 1 deficiency compared with other urea cycle defects. Affected patients manifest hyperargininemia and infrequent episodes of hyperammonemia. Patients typically suffer from neurological impairment with cortical and pyramidal tract deterioration, spasticity, loss of ambulation, seizures and intellectual disability; death is less common than with other urea cycle disorders. In a mouse model of arginase I deficiency, the onset of symptoms begins with weight loss and gait instability, which progresses toward development of tail tremor with seizure-like activity; death typically occurs at about 2 weeks of life. Adeno-associated viral vector gene replacement strategies result in long-term survival of mice with this disorder. With neonatal administration of vector, the viral copy number in the liver greatly declines with hepatocyte proliferation in the first 5 weeks of life. Although the animals do survive, it is not known from a functional standpoint how well the urea cycle is functioning in the adult animals that receive adeno-associated virus. In these studies, we administered [1-13C] acetate to both littermate controls and adeno-associated virus-treated arginase 1 knockout animals and examined flux through the urea cycle. Circulating ammonia levels were mildly elevated in treated animals. Arginine and glutamine also had perturbations. Assessment 30 min after acetate administration demonstrated that ureagenesis was present in the treated knockout liver at levels as low at 3.3% of control animals. These studies demonstrate that only minimal levels of hepatic arginase activity are necessary for survival and ureagenesis in arginase-deficient mice and that this level of activity results in control of circulating ammonia. These results may have implications for potential therapy in humans with arginase deficiency.

Five novel mutations in ARG1 gene in Chinese patients of argininemia.

BACKGROUND: Argininemia is an autosomal recessive genetic disorder caused by hepatocyte arginase deficiency. It could be detected by blood amino acids analysis (high arginine) and confirmed by molecular diagnosis. The clinical manifestations in patients are similar to cerebral palsy so the diagnosis is usually much delayed. Reports of argininemia from mainland China are few, and genetic analyses have not been reported. PATIENTS AND METHODS: Five Chinese patients with argininemia were investigated. They had progressive spastic tetraplegia, poor physical growth from 1 month to 4 years. When argininemia was found at the ages of 4 to 12 years, four of patients had mental retardation, and three had seizures. RESULTS: Elevated blood arginine and significantly decreased erythrocyte arginase activity in five patients confirmed the diagnosis of arginase deficiency. Liver dysfunction was found in four patients, two of whom had mildly elevated blood ammonia levels. Cranial magnetic resonance imaging showed progressive cerebral atrophy in three patients. Six mutations in the ARG1 gene were identified, of which only one (c.703 G>A, p.G235R) in exon 7 has been reported before; c.34 G>T (p.G12X) in exon 1, c.67delG (p.G23fsX31) in exon 2, c.539G>C (p.R180 T) in exon 5, c.374C>T (p.A125 V) in exon 4, and c.646-649del CTCA (p.T215fsX219) in exon 6 were novel mutations. CONCLUSIONS: Argininemia is one of the few treatable causes of pediatric spastic paraparesis. Early metabolic investigation is very important to reach a diagnosis and better outcome. Five Chinese patients with late-diagnosed argininemia were reported. The mutation spectrum of ARG1 gene should be different from other populations.

Analysis of novel ARG1 mutations causing hyperargininemia and correlation with arginase I activity in erythrocytes.

Hyperargininemia (HA) is an autosomal recessive disease that typically has a clinical presentation that is distinct from other urea cycle disorders. It is caused by the deficient activity of the enzyme arginase I, encoded by the gene ARG1. We screened for ARG1 mutations and measured erythrocyte enzyme activity in a series of 16 Brazilian HA patients. Novel mutations, in addition to previously described missense mutations, were analysed for their effect on the structure, stability and/or function of arginase I (ARG1) using bioinformatics tools. Three previously reported mutations were found (p.R21X; p.I11T and p.W122X), and five novel mutations were identified (p.G27D; p.G74V; p.T134I; p.R308Q; p.I174fs179). The p.T134I mutation was the most frequent in the Brazilian population. Patients carrying the p.R308Q mutation had higher residual ARG1 decreased activity, but presented no distinguishable phenotype compared to the other patients. Bioinformatics analyses revealed that missense mutations (1) affect the ARG1 active site, (2) interfere with the stability of the ARG1 folded conformation or (3) alter the quaternary structure of the ARG1. Our study reinforced the role of Arg308 residue for assembly of the ARG1 homotrimer. The panel of heterogeneous ARG1 mutations that cause HA was expanded, nevertheless a clear genotype-phenotype correlation was not observed in our series.

Recurrent unexplained hyperammonemia in an adolescent with arginase deficiency.

OBJECTIVES: This report investigates the etiology of recurrent episodic elevations in plasma ammonia in an adolescent male with arginase deficiency as there were concerns regarding pre-analytical and analytical perturbations of ammonia measurements. There were repeated discrepancies between the magnitude of his ammonia levels and the severity of his clinical signs of hyperammonemia. PATIENT AND METHODS: The patient is a fourteen-year-old arginase-deficient male diagnosed at three years of age. Since 2008 (when he reached 10 years of age), there appeared to be an increase in the frequency of hospitalizations with elevated ammonia. A typical emergency visit with initial ammonia of 105 µmol/L (reference interval: 16-47 µmol/L) is illustrated. Pre-analytical and analytical procedures for the patient's sample handling were retrospectively examined. His ammonia levels were compiled since diagnosis. The frequency of his initial or peak ammonia levels greater than two times (94 µmol/L) or four times (188 µmol/L) the upper limit of normal was computed. Student t-test was used to calculate the significance of the differences before 2008 and since 2008. RESULTS: One out of eleven and ten out of 19 hospitalizations had initial ammonia greater than two times normal before and after 2008, respectively. Both the patient's overall ammonia and peak ammonia levels are significantly higher since 2008 (p value <0.001 for both) than those before 2008. CONCLUSIONS: To our knowledge, few adolescent males with arginase deficiency experience recurrent episodes of hyperammonemia requiring intravenous nitrogen scavenging agents. We hope that this study provides new insights into the natural history of arginase deficiency and the management of such patients.

Arginase I deficiency: severe infantile presentation with hyperammonemia: more common than reported?

Enzyme defects of the urea cycle typically present with significant hyperammonemia and its associated toxicity, in the first few months of life. However, arginase I (ARG1) deficiency, a rare autosomal recessive disorder, has classically been the exception. ARG1 deficiency usually presents later in life with spasticity, seizures, failure to thrive and developmental regression. Neonatal and early infantile presentation of ARG1 deficiency with severe hyperammonemia remains rare and only six such cases have been described. We report a severely affected infant with ARG1 deficiency who presented at 6 weeks of age with lethargy, poor feeding and severe encephalopathy caused by hyperammonemia. The clinical and biochemical features of the proband and six other previously reported cases with neonatal or infantile-onset presentation of ARG1 deficiency with hyperammonemia are reviewed. In addition, the clinical spectrum of seven previously unpublished patients with later onset ARG1 deficiency, who also experienced recurrent hyperammonemia, is presented. Several biochemical abnormalities have been postulated to play a role in the pathogenesis of the neurological changes in ARG1 deficiency including hyperargininemia, elevated guanidino compounds and elevated glutamine levels, as well as the hyperammonemia. The index case demonstrated many of these. The cases reviewed here suggest a genotype/phenotype correlation and advocate for the addition of arginine as a primary target in newborn screening programs.

A long-term survival case of arginase deficiency with severe multicystic white matter and compound mutations.

Neuropathology and neuroimaging of long-term survival cases of arginase deficiency are rarely reported. The magnetic resonance imaging (MRI) of our case showed severe multicystic white matter lesions with cortical atrophy, which were more severe compared with previous reports. In this patient, low-protein diet successfully reduced hyperammonemia, but hyperargininemia persisted. These severe neurological and MRI findings may be explained by a compound heterozygote, inheriting both of severe mutant alleles from her parents.

Guanidino compound levels in blood, cerebrospinal fluid, and post-mortem brain material of patients with argininemia.

The paucity of hyperammonemic crises together with spasticity, only seen in human arginase I deficient patients and not in patients with other urea cycle disorders, forces a search for candidates other than ammonia to associate with the pathophysiology and symptomatology. Therefore, we determined arginine together with some catabolites of arginine in blood and cerebrospinal fluid of these patients as well as in extremely rare post-mortem brain material of two patients with argininemia. The levels of alpha-keto-delta-guanidinovaleric acid, argininic acid and alpha-N-acetylarginine correlate with the arginine levels in blood and cerebrospinal fluid of patients with imposed or spontaneous protein restriction. The levels in blood are higher than the upper limit of normal in all studied patients. In addition to the highly increased levels of these same compounds in blood of a child with argininemia, the increase of guanidinoacetic acid, 24h before death, is remarkable. However, the manifest increases of these studied catabolites of arginine are not seen in post-mortem brain material of the same pediatric patient. Otherwise a clear increase of guanidinoacetic acid in post-mortem brain material of an adult patient was shown. A similar, comparable increase of homoarginine in both studied post-mortem brain materials is observed. Therefore the study of the pathobiochemistry of arginine in argininemia must be completed in the future by the determination of the end catabolites of the nitric oxide and agmatine biosynthesis pathways in the knockouts as well as in the patients to evaluate their role, together with the here studied catabolites, as candidates for association with pathophysiology and symptomatology.

Amino acids in CSF and plasma in hyperammonaemic coma due to arginase1 deficiency.

UNLABELLED: We report the CSF and plasma amino acid concentrations and their ratios in a male patient with arginase1 deficiency with an unusual early presentation at 34 days of age. He developed hyperammonaemic coma (ammonia >400 µmol/L; normal <90 µmol/L) on postnatal day 35. CSF and plasma concentrations were assayed by ion-exchange chromatography on day 36. Arginine was increased both in plasma (971 µmol/L; controls (mean ± 2SD) 50 ± 42) and in CSF (157 µmol/L; controls 19 ± 8.6), resulting in a normal CSF/plasma ratio of 0.16 (controls 0.41 ± 0.26). Interestingly, glutamine was disproportionately high in CSF (3114 µmol/L; controls 470 ± 236) but normal in plasma (420 µmol/L; controls 627 ± 246); the ratio exceeded unity (7.4; controls 0.76 ± 0.31). The CSF/plasma ratios of most neutral amino acids were elevated but not those of the imino- and of the dibasic amino acids lysine and ornithine. The mechanism leading to the increase of most neutral amino acids in brain is not known. CONCLUSION: A normal glutamine in plasma does not exclude an increased concentration in CSF; it could be useful to ascertain by MRS that a high CSF glutamine concentration truly reflects a high concentration in brain tissue for better understanding its pathogenesis.

Increased plasma and tissue guanidino compounds in a mouse model of hyperargininemia.

In humans, arginase I (AI)-deficiency results in hyperargininemia, a metabolic disorder with symptoms of progressive neurological and intellectual impairment, spasticity, persistent growth retardation, and episodic hyperammonemia. A deficiency of arginase II (AII) has never been detected and the clinical disorder, if any, associated with its deficiency has not been defined. Since the spasticity and paucity of hyperammonemic crises seen in human AI-deficient patients are not features of the other urea cycle disorders, the likelihood of ammonia as the main neuropathogenic agent becomes extremely low, and the modest elevations of arginine seen in the brains of our mouse model of hyperargininemia make it an unlikely candidate as well. Specific guanidino compounds, direct or indirect metabolites of arginine, are elevated in the blood of patients with uremia. Other guanidino compounds are also increased in plasma and cerebrospinal fluid of hyperargininemic patients making them plausible as neurotoxins in these disorders. We analyzed several guanidino compounds in our arginase single and double knockout animals and found that alpha-keto-delta-guanidinovaleric acid, alpha-N-acetylarginine, and argininic acid were increased in the brain tissue from the AI knockout and double knockout animals. Several compounds were also increased in the plasma, liver, and kidneys. This is the first time that several of the guanidino compounds have been shown to be elevated in the brain tissue of an arginase-deficient mammal, and it further supports their possible role as the neuropathogenic agents responsible for the complications seen in arginase deficiency.

L-NAME administration prevents the inhibition of nucleotide hydrolysis by rat blood serum subjected to hyperargininemia.

The main objective of the present study was to evaluate the in vivo and in vitro effect of Arg on serum nucleotide hydrolysis. The action of Nomega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase, on the effects produced by Arg was also examined. Sixty-day-old rats were treated with a single or a triple (with an interval of 1 h between each injection) intraperitoneal injection of saline (group I), Arg (0.8 g/kg) (group II), L-NAME (2.0 mg/kg or 20 mg/kg) (group III) or Arg (0.8 g/kg) plus L-NAME (2.0 mg/kg or 20 mg/kg) (group IV) and were killed 1 h later. The present results show that a triple Arg administration decreased ATP, ADP and AMP hydrolysis. Simultaneous injection of L-NAME (20 mg/kg) prevented such effects. Arg in vitro did not alter nucleotide hydrolysis. It is suggested that in vivo Arg administration reduces nucleotide hydrolysis in rat serum, probably through nitric oxide or/and peroxynitrite formation.