Arginase deficiency-An unheralded cause of developmental epileptic encephalopathy.

Arginase deficiency, which leads to hyperargininaemia is a rare urea cycle disorder caused by a mutation in the ARG1 gene. It is an under-recognized cause of pediatric developmental epileptic encephalopathy, with the key coexistent clinical features being developmental delay or regression and spasticity. Detection of ARG1 gene mutation on genetic testing is the confirmatory diagnostic test. However, elevated levels of plasma arginine and low plasma arginase level can be considered as biochemical markers for diagnosis. We present two cases of arginase deficiency with genetically confirmed ARG1 mutation in one and biochemical confirmation in both. As the spectrum of epilepsy in arginase deficiency has been less explored, we attempted to elucidate the novel electroclinical features and syndromic presentations in these patients. Informed consent was obtained from families of patients. Electroclinical diagnosis was consistent with Lennox Gastaut syndrome (LGS) in the first patient while the second patient had refractory atonic seizures with electrophysiological features consistent with developmental and epileptic encephalopathy. Though primary hyperammonaemia is not a consistent feature, secondary hyperammonaemia in the setting of infectious triggers and drugs like valproate (valproate sensitivity) has been well described as also observed in our patient. In the absence of an overt antecedent in a child with spasticity and seizure disorder, with a progressive course consistent with a developmental epileptic encephalopathy, arginase deficiency merits consideration. Diagnosis often has important therapeutic implications with respect to dietary management and choice of the appropriate antiseizure medications.

Arginase deficiency in Bulgaria: first cases and potential endemic region for the disorder.

Arginase deficiency is an autosomal recessive urea cycle disorder caused by pathogenic variants in the ARG1 gene. The clinical features of the disease include spasticity, tremour, ataxia, hypotonia, microcephaly and seizures. Growth delay can also be observed in the affected individuals. Here we describe the results from molecular-genetic analysis of two patients with arginase deficiency. In the first case, we reported a novel homozygous missense variant c.775G>A p.(Gly259Ser) in a patient with Bulgarian ethnic origin. In the second case, a novel homozygous splice site variant c.329+1G>A was detected in a patient from a consanguineous family of Roma ethnic origin. A hundred samples of newborns of Roma origin were screened for variant c.329+1G>A and one individual was found to be a heterozygous carrier of variant c.329+1G> A. The results from this study indicated the necessity for screening of the Roma population with respect to the disease arginase deficiency in Bulgaria.

The role and control of arginine levels in arginase 1 deficiency.

Arginase 1 Deficiency (ARG1-D) is a rare urea cycle disorder that results in persistent hyperargininemia and a distinct, progressive neurologic phenotype involving developmental delay, intellectual disability, and spasticity, predominantly affecting the lower limbs and leading to mobility impairment. Unlike the typical presentation of other urea cycle disorders, individuals with ARG1-D usually appear healthy at birth and hyperammonemia is comparatively less severe and less common. Clinical manifestations typically begin to develop in early childhood in association with high plasma arginine levels, with hyperargininemia (and not hyperammonemia) considered to be the primary driver of disease sequelae. Nearly five decades of clinical experience with ARG1-D and empirical studies in genetically manipulated models have generated a large body of evidence that, when considered in aggregate, implicates arginine directly in disease pathophysiology. Severe dietary protein restriction to minimize arginine intake and diversion of ammonia from the urea cycle are the mainstay of care. Although this approach does reduce plasma arginine and improve patients' cognitive and motor/mobility manifestations, it is inadequate to achieve and maintain sufficiently low arginine levels and prevent progression in the long term. This review presents a comprehensive discussion of the clinical and scientific literature, the effects and limitations of the current standard of care, and the authors' perspectives regarding the past, current, and future management of ARG1-D.

A Delayed Presentation of Arginase Deficiency Presenting with Status Epilepticus.

Arginase 1(ARG1) deficiency is a rare disorder of the urea cycle. The presentation is usually late, leading to loss of intellectual milestones, spasticity and liver involvement. Hyperammonemic crises are rarely encountered. We herein present a case of a 16-year immigrant girl of Syrian origin who was evaluated for acute onset of fever, vomiting, and seizures. Laboratory analyses showed slightly elevated lactate, creatine kinase, and coagulation parameters. Ammonium levels were also moderately increased. On 5th day of admission, she went into an encephalopathic state. Blood amino acid analysis showed highly elevated arginine levels. An increased level of orotic acid was found in urine organic acid analysis. Molecular genetic analysis of ARG1 gene showed a novel homozygous mutation. Although the presentation of ARG1 deficiency is usually chronic in the majority of patients, an acute crisis of encephalopathy due to hyperammonemia may occur and delayed diagnosis may lead to irreversible neurological damage. Key Words: Urea cycle disorder, Hyperammonemia, Argininemia, Encephalopathy.

Epidemiology, methods of diagnosis, and clinical management of patients with arginase 1 deficiency (ARG1-D): A systematic review.

BACKGROUND: Arginase 1 Deficiency (ARG1-D) is a rare, progressive, metabolic disorder that is characterized by devastating manifestations driven by elevated plasma arginine levels. It typically presents in early childhood with spasticity (predominately affecting the lower limbs), mobility impairment, seizures, developmental delay, and intellectual disability. This systematic review aims to identify and describe the published evidence outlining the epidemiology, diagnosis methods, measures of disease progression, clinical management, and outcomes for ARG1-D patients. METHODS: A comprehensive literature search across multiple databases such as MEDLINE, Embase, and a review of clinical studies in ClinicalTrials.gov (with results reported) was carried out per PRISMA guidelines on 20 April 2020 with no date restriction. Pre-defined eligibility criteria were used to identify studies with data specific to patients with ARG1-D. Two independent reviewers screened records and extracted data from included studies. Quality was assessed using the modified Newcastle-Ottawa Scale for non-comparative studies. RESULTS: Overall, 55 records reporting 40 completed studies and 3 ongoing studies were included. Ten studies reported the prevalence of ARG1-D in the general population, with a median of 1 in 1,000,000. Frequently reported diagnostic methods included genetic testing, plasma arginine levels, and red blood cell arginase activity. However, routine newborn screening is not universally available, and lack of disease awareness may prevent early diagnosis or lead to misdiagnosis, as the disease has overlapping symptomology with other diseases, such as cerebral palsy. Common manifestations reported at time of diagnosis and assessed for disease progression included spasticity (predominately affecting the lower limbs), mobility impairment, developmental delay, intellectual disability, and seizures. Severe dietary protein restriction, essential amino acid supplementation, and nitrogen scavenger administration were the most commonly reported treatments among patients with ARG1-D. Only a few studies reported meaningful clinical outcomes of these interventions on intellectual disability, motor function and adaptive behavior assessment, hospitalization, or death. The overall quality of included studies was assessed as good according to the Newcastle-Ottawa Scale. CONCLUSIONS: Although ARG1-D is a rare disease, published evidence demonstrates a high burden of disease for patients. The current standard of care is ineffective at preventing disease progression. There remains a clear need for new treatment options as well as improved access to diagnostics and disease awareness to detect and initiate treatment before the onset of clinical manifestations to potentially enable more normal development, improve symptomatology, or prevent disease progression.

Arginase 1 Deficiency: using genetic databases as a tool to establish global prevalence.

BACKGROUND/OBJECTIVE: Arginase 1 Deficiency (ARG1-D) is a rare inherited metabolic disease with progressive, devastating neurological manifestations with early mortality and high unmet need. Information on prevalence is scarce and highly variable due to limited newborn screening (NBS) availability, variability of arginine levels in the first days of life, and high rates of misdiagnosis. US birth prevalence was recently estimated via indirect methods at 1.1 cases per million live births. Due to the autosomal recessive nature of ARG1-D we hypothesize that the global prevalence may be more accurately estimated using genetic population databases. METHODS: MEDLINE and EMBASE were systematically searched for previously reported disease variants. Disease variants in ARG1-D were annotated wherever possible with allele frequencies from gnomAD. Ethnicity-specific prevalence was calculated using the Hardy-Weinberg equation and applied to generate country-specific carrier frequencies for 38 countries. Finally, documented consanguinity rates were applied to establish a birth prevalence for each country. RESULTS: 133 of 228 (58%) known causative alleles were annotated with ethnic-specific frequencies. Global birth prevalence for ARG1-D was estimated at 2.8 cases per million live births (country-specific estimates ranged from 0.92 to 17.5) and population prevalence to be 1.4 cases per million people (approximately 1/726,000 people). Birth prevalence estimates were dependent on population demographics and consanguinity rate. CONCLUSION: Birth prevalence of ARG1-D based on genetic database analysis was estimated to be more frequent than previous NBS studies have indicated. There was a higher degree of confidence in North American and European countries due to availability of genetic databases and mutational analysis versus other regions. These findings suggest the need for greater disease education around signs and manifestations of ARG1-D, as well as more widespread testing and standardization of screening for this severe disease in order to appropriately identify patients prior to disease progression.

Case series of arginase 1 deficiency: Expanding the spectrum in hyperargininemia.

BACKGROUND: Arginase-1 deficiency is a rare, autosomal recessively inherited disorder of the urea cycle. In this study, we describe the clinical and molecular details of six patients who were diagnosed with argininemia, and we describe two of the patients with hyperargininemia who carried two novel variations of the Arginase-1 gene. METHODS: The clinical and demographic characteristics of the patients were retrospectively evaluated. RESULTS: The ages of the six patients ranged from 1 day to 20 years, and each patient had consanguineous parents. Neuromotor retardation and spastic paraparesis were found in all patients except one, who was diagnosed prenatally. Hyperargininemia was present in all patients. Urinary orotic acid excretion was increased in four of the six patients. The diagnosis was confirmed by genetic analysis in all the patients. Elevated liver enzymes were detected in three patients and blood urea nitrogen levels were normal in each of the six patients. CONCLUSIONS: In this study, we describe the two patients with hyperargininemia who carried two novel variations of the ARG1 gene. Also, we present a patient with normal neurodevelopment who was diagnosed prenatally and treated at an early stage of the disease.

Two Japanese siblings with arginase-1 deficiency identified using a novel frameshift mutation of ARG1 (p.Lys41Thrfs∗2).

We described two Japanese siblings with arginase-1 (ARG1) deficiency. A 10-year-old girl (the proband and elder sister) was referred to our hospital complaining about her short stature. We diagnosed her with ARG1 deficiency, possibly with elevated levels of blood ammonia and plasma arginine. Her younger sister was found to have spastic paraparesis in her lower extremities and short stature at the age of 4 years. The younger sister also had high levels of plasma arginine, instead of normal levels of blood ammonia. Interestingly, they also prefer to avoid protein-rich foods such as meat, soybeans, cow milk, and dairy products. Genetic testing identified compound heterozygous mutations (c.121_122insCTT [p.Lys41Thrfs∗2] and c.298G>A [p.Asp100Asn]) in the ARG1 gene. The ARG1 mutation of p.Lys41Thrfs∗2 is a novel pathogenic mutation according to open databases and literature.

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.

Neurological Deterioration in Three Siblings: Exploring the Spectrum of Argininemia.

Argininemia or hyperargininemia is a urea cycle disorder caused by deficiency of the enzyme arginase 1. It is inherited in an autosomal recessive fashion. It commonly leads to spastic diplegia in childhood, but other important features include cognitive deterioration and epilepsy. Unlike other disorders of the urea cycle, hyperammonemia is not prominent. The authors report three siblings with genetically proven argininemia who presented with diverse phenotypes but with spasticity being a common feature. Sibling 1 developed motor regression in early childhood, sibling 2 developed delayed motor milestones from early infancy, whereas sibling 3 had global developmental delay in late infancy after a period of normal development. All siblings had mild hyperammonemia only. Early recognition is imperative, not only to initiate ammonia scavenging therapy which may lead to definite clinical improvement, but also to provide genetic counselling.

Development of a Protein Scaffold for Arginine Sensing Generated through the Dissection of the Arginine-Binding Protein from Thermotoga maritima.

Arginine is one of the most important nutrients of living organisms as it plays a major role in important biological pathways. However, the accumulation of arginine as consequence of metabolic defects causes hyperargininemia, an autosomal recessive disorder. Therefore, the efficient detection of the arginine is a field of relevant biomedical/biotechnological interest. Here, we developed protein variants suitable for arginine sensing by mutating and dissecting the multimeric and multidomain structure of Thermotoga maritima arginine-binding protein (TmArgBP). Indeed, previous studies have shown that TmArgBP domain-swapped structure can be manipulated to generate simplified monomeric and single domain scaffolds. On both these stable scaffolds, to measure tryptophan fluorescence variations associated with the arginine binding, a Phe residue of the ligand binding pocket was mutated to Trp. Upon arginine binding, both mutants displayed a clear variation of the Trp fluorescence. Notably, the single domain scaffold variant exhibited a good affinity (~3 µM) for the ligand. Moreover, the arginine binding to this variant could be easily reverted under very mild conditions. Atomic-level data on the recognition process between the scaffold and the arginine were obtained through the determination of the crystal structure of the adduct. Collectively, present data indicate that TmArgBP scaffolds represent promising candidates for developing arginine biosensors.

A novel compound heterozygous mutation in the arginase-1 gene identified in a Chinese patient with argininemia: A case report.

INTRODUCTION: Arginineemia, also known as arginase deficiency, is a rare autosomal recessive metabolic disease. The diagnosis sometimes may be delayed due to atypical clinical manifestations. Confirmation of arginineemia depends on genetic testing. PATIENT CONCERNS: We reported a Chinese male child presenting with hyperargininemia and progressive spastic diplegia, who has a novel compound heterozygous mutation in the arginase-1 (ARG1) gene (c.263-266delAGAA, p.K88Rfs45;c.674T>C,p.L216P), respectively, coming from his mother and father. DIAGNOSIS: The patient was diagnosed with argininemia with a novel compound homozygous mutation of the ARG1 gene at the age of 12 years. INTERVENTIONS: The patient had a low-protein diet (0.8 g/kg/day). Baclofen, eperisone hydrochloride, botulinum toxin, and rehabilitation training were used to improve his spastic diplegia symptoms for 3 months. OUTCOMES: The patient's blood arginine was still high after 3 months' low-protein diet. His spastic diplegia symptoms had not aggravated after 3 months' treatment. CONCLUSIONS: Argininemia should be considered in a patient with slowly progressive neurologic manifestations, especially spastic diplegia. This case also suggests that tandem mass spectrometry should be used as an effective tool in the validity of neonatal screening for early diagnosis.

Arginase impedes the resolution of colitis by altering the microbiome and metabolome.

Arginase 1 (Arg1), which converts l-arginine into ornithine and urea, exerts pleiotropic immunoregulatory effects. However, the function of Arg1 in inflammatory bowel disease (IBD) remains poorly characterized. Here, we found that Arg1 expression correlated with the degree of inflammation in intestinal tissues from IBD patients. In mice, Arg1 was upregulated in an IL-4/IL-13- and intestinal microbiota-dependent manner. Tie2-Cre Arg1fl/fl mice lacking Arg1 in hematopoietic and endothelial cells recovered faster from colitis than Arg1-expressing (Arg1fl/fl) littermates. This correlated with decreased vessel density, compositional changes in intestinal microbiota, diminished infiltration by myeloid cells, and an accumulation of intraluminal polyamines that promote epithelial healing. The proresolving effect of Arg1 deletion was reduced by an l-arginine-free diet, but rescued by simultaneous deletion of other l-arginine-metabolizing enzymes, such as Arg2 or Nos2, demonstrating that protection from colitis requires l-arginine. Fecal microbiota transfers from Tie2-Cre Arg1fl/fl mice into WT recipients ameliorated intestinal inflammation, while transfers from WT littermates into Arg1-deficient mice prevented an advanced recovery from colitis. Thus, an increased availability of l-arginine as well as altered intestinal microbiota and metabolic products accounts for the accelerated resolution from colitis in the absence of Arg1. Consequently, l-arginine metabolism may serve as a target for clinical intervention in IBD patients.

Hyperargininemic Encephalopathy with Unique Clinical Presentation and Novel Genetic Mutations.

Hyperargininemia is a urea cycle disorder that has rarely been reported in adults. We present a case of arginase deficiency disorder in a 32-year man with metabolic encephalopathy. He presented with progressive limb spasticity, changes in personality, cognitive decline (impaired judgement, executive and language dysfunction) and pseudo-bulbar affect. He deteriorated to an akinetic mute and rigid state. MRI brain was suggestive of a metabolic disorder. Hyperammonemia was present, blood arginine levels were elevated, and serum arginase levels were reduced. The standard argI gene mutations were absent but rs2781666 (G/T) and rs2608897 (C/T) variations were noted in this patient. Hyperargininemic encephalopathy may present in adults and with atypical features. It should be kept in the differential diagnosis of metabolic encephalopathy in adults. Key Words: Metabolic encephalopathy, Pseudobulbar affect, Arginase deficiency, Hyperammonemia, Urea cycle.

Defective arginine metabolism impairs mitochondrial homeostasis in Caenorhabditiselegans.

Arginine catabolism involves enzyme-dependent reactions in both mitochondria and the cytosol, defects in which may lead to hyperargininemia, a devastating developmental disorder. It is largely unknown if defective arginine catabolism has any effects on mitochondria. Here we report that normal arginine catabolism is essential for mitochondrial homeostasis in Caenorhabditiselegans. Mutations of the arginase gene argn-1 lead to abnormal mitochondrial enlargement and reduced adenosine triphosphate (ATP) production in C. elegans hypodermal cells. ARGN-1 localizes to mitochondria and its loss causes arginine accumulation, which disrupts mitochondrial dynamics. Heterologous expression of human ARG1 or ARG2 rescued the mitochondrial defects of argn-1 mutants. Importantly, genetic inactivation of the mitochondrial basic amino acid transporter SLC-25A29 or the mitochondrial glutamate transporter SLC-25A18.1 fully suppressed the mitochondrial defects caused by argn-1 mutations. These findings suggest that mitochondrial damage probably contributes to the pathogenesis of hyperargininemia and provide clues for developing therapeutic treatments for hyperargininemia.

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.

[Analysis of AGR1 gene variants in an infant with early-onset argininemia].

OBJECTIVE: To explore the genetic basis for an infant with early-onset argininemia. METHODS: Potential variant was detected with an Ion Torrent semiconductor sequencer using a gene panel for inherited diseases. Suspected variants were verified by Sanger sequencing. RESULTS: Genetic testing indicated that he has carried c.560+2T>C and c.811T>C compound heterozygous variant of the AGR1 gene, which were inherited from his father and mother, respectively. Among these, c.560+2T>C was suspected to be pathogenic, while c.811T>C was of unknown clinical significance, and both were not reported previously. CONCLUSION: The c.560+2T>C and c.811T>C compound heterozygous variants of the AGR1 gene probably underlies the argininemia in this child. Above finding has enriched the variant spectrum of the AGR1 gene.

Hepatic arginase deficiency fosters dysmyelination during postnatal CNS development.

Deficiency of arginase is associated with hyperargininemia, and prominent features include spastic diplegia/tetraplegia, clonus, and hyperreflexia; loss of ambulation, intellectual disability and progressive neurological decline are other signs. To gain greater insight into the unique neuromotor features, we performed gene expression profiling of the motor cortex of a murine model of the disorder. Coexpression network analysis suggested an abnormality with myelination, which was supported by limited existing human data. Utilizing electron microscopy, marked dysmyelination was detected in 2-week-old homozygous Arg1-KO mice. The corticospinal tract was found to be adversely affected, supporting dysmyelination as the cause of the unique neuromotor features and implicating oligodendrocyte impairment in a deficiency of hepatic Arg1. Following neonatal hepatic gene therapy to express Arg1, the subcortical white matter, pyramidal tract, and corticospinal tract all showed a remarkable recovery in terms of myelinated axon density and ultrastructural integrity with active wrapping of axons by nearby oligodendrocyte processes. These findings support the following conclusions: arginase deficiency is a leukodystrophy affecting the brain and spinal cord while sparing the peripheral nervous system, and neonatal AAV hepatic gene therapy can rescue the defects associated with myelinated axons, strongly implicating the functional recovery of oligodendrocytes after restoration of hepatic arginase activity.