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.

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.

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.

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.

[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.

A new metabolic disorder in human cationic amino acid transporter-2 that mimics arginase 1 deficiency in newborn screening

PURPOSE

We report a patient with a human cationic amino acid transporter 2 (CAT-2) defect discovered due to a suspected arginase 1 deficiency observed in newborn screening (NBS).

METHODS

A NBS sample was analyzed using tandem mass spectrometry. Screen results were confirmed by plasma and urine amino acid quantification. Molecular diagnosis was done using clinical exome sequencing. Dimethylated arginines were determined by HPLC and nitrate/nitrite levels by a colorimetric assay. The metabolomic profile was analyzed using 1D nuclear magnetic resonance spectroscopy.

RESULTS

A Spanish boy of nonconsanguineous parents had high arginine levels in a NBS blood sample. Plasma and urinary cationic amino acids were high. Arginase enzyme activity in erythrocytes was normal and no pathogenic mutations were identified in the ARG1 gene. Massive parallel sequencing detected two loss-of-function mutations in the SLC7A2 gene. Currently, the child receives a protein-controlled diet of 1.2 g/kg/day with protein-and amino-acid free infant formula, 30 g/day, and is asymptomatic.

CONCLUSION

We identified a novel defect in human CAT-2 due to biallelic pathogenic variants in the SLC7A2 gene. The characteristic biochemical profile includes high plasma and urine arginine, ornithine, and lysine levels. NBS centers should know of this disorder since it can be detected in arginase 1 deficiency screening.

Recurrent hepatic failure and status epilepticus: an uncommon presentation of hyperargininemia

Argininemia is a rare hereditary disease due to a deficiency of hepatic arginase, which is the last enzyme of the urea cycle and hydrolyzes arginine to ornithine and urea. Herein we report a patient with arginase I (ARG1) deficiency who presented with recurrent nonconvulsive status epilepticus and liver failure. A novel homozygous frameshift mutation c.703_707delGGACTinsAGACTGGACC (p.G235Rfs*20) was detected.

A case report of neurological complications owing to lately diagnosed hyperargininemia emphasizing the role of national neonatal screening policies in the kingdom of Bahrain

INTRODUCTION

Arginine is an essential amino acid that plays an important role in various body functions including cell division, wound healing, removal of ammonia, immune function, and release of hormones. Hyperargininemia, an autosomal recessive genetic disorder, is considered one of the least common urea cycle disorders. It rarely presents in the neonatal period but rather appears in children at the age between 2 and 4 years.

CASE PRESENTATION

Herein, we demonstrate a case of a 14-year-old female who presented to the neurology clinic with several neurological complications, which were found to be a consequence of high levels of arginine discovered after performing a metabolic screening test. The hyperargininemia was because of a point mutation of A1 gene on 6q23 resulting in deficiency in arginase enzyme. The complications of this lately diagnosed case of hyperargininemia would have been avoided if a newborn screen were done as a part of a national program.

CONCLUSION

This study presented certain neurological complications in a 14-year-old female who was lately diagnosed with hyperargininemia. Out case report strongly emphasizes the importance of establishing a national neonatal screening policy to ensure early detection of inherited metabolic disorders, in particular those which can be easily treated, in the Kingdom of Bahrain.

Argininemia as a cause of severe chronic stunting and partial growth hormone deficiency (PGHD): A case report

RATIONALE

Argininemia is an autosomal recessive inherited disorder of the urea cycle. Because of its atypical symptoms in early age, diagnosis can be delayed until the typical chronic manifestations - including spastic diplegia, deterioration in cognitive function, and epilepsy - appear in later childhood.

PATIENT CONCERNS

A Chinese boy initially presented with severe stunting and partial growth hormone deficiency (PGHD) at 3 years old and was initially treated with growth hormone replacement therapy. Seven years later (at 10 years old), he presented with spastic diplegia, cognitive function lesions, epilepsy, and peripheral neuropathy.

DIAGNOSES

Ultimately, the patient was diagnosed with argininemia with homozygous mutation (c.32T>C) of the ARG1 gene at 10 years old. Blood tests showed mildly elevated blood ammonia and creatine kinase, and persistently elevated bilirubin.

INTERVENTIONS

Protein intake was limited to 0.8 g/kg/day, citrulline (150-200 mg [kg d]) was prescribed.

OUTCOMES

The patient's mental state and vomiting had improved after 3 months treatment. At 10 years and 9 month old, his height and weight had reached 121cm and 22kg, respectively, but his spastic diplegia symptoms had not improved.

LESSONS

This case demonstrates that stunting and PGHD that does not respond to growth hormone replacement therapy might hint at inborn errors of metabolism (IEM). IEM should also be considered in patients with persistently elevated bilirubin with or without abnormal liver transaminase, as well as elevated blood ammonia and creatine kinase, in the absence of hepatic disease.

Hyperargininemia: 7-month follow-up under sodium benzoate therapy in an Italian child presenting progressive spastic paraparesis, cognitive decline, and novel mutation in ARG1 gene

BACKGROUND

Hyperargininemia due to mutations in ARG1 gene is an autosomal recessive inborn error of metabolism caused by a defect in the final step of the urea cycle. Common clinical presentation is a variable association of progressive spastic paraparesis, epilepsy, and cognitive deficits.

METHODS

We describe the clinical history of an Italian child presenting progressive spastic paraparesis, carrying a new homozygous missense mutation in the ARG1 gene. A detailed clinical, biochemical, and neurophysiological follow-up after 7 months of sodium benzoate therapy is reported.

RESULTS

Laboratory findings, gait abnormalities, spastic paraparesis, and electroencephalographic and neurophysiological abnormalities remained quite stable over the follow-up. Conversely, a mild cognitive deterioration has been detected by means of the neuropsychologic assessment.

CONCLUSIONS

Further longitudinal studies by means of longer follow-up and using clinical, biochemical, radiological, and neurophysiological assessments are needed in such patients to describe natural history and monitor the effects of treatments.

Arginase 2 deficiency reduces hyperoxia-mediated retinal neurodegeneration through the regulation of polyamine metabolism

Hyperoxia treatment has been known to induce neuronal and glial death in the developing central nervous system. Retinopathy of prematurity (ROP) is a devastating disease in premature infants and a major cause of childhood vision impairment. Studies indicate that, in addition to vascular injury, retinal neurons are also affected in ROP. Using an oxygen-induced retinopathy (OIR) mouse model for ROP, we have previously shown that deletion of the arginase 2 (A2) significantly reduced neuro-glial injury and improved retinal function. In the current study, we investigated the mechanism of A2 deficiency-mediated neuroprotection in the OIR retina. Hyperoxia treatment has been known to induce neuronal death in neonates. During the hyperoxia phase of OIR, a significant increase in the number of apoptotic cells was observed in the wild-type (WT) OIR retina compared with A2-deficient OIR. Mass spectrometric analysis showed alterations in polyamine metabolism in WT OIR retina. Further, increased expression level of spermine oxidase was observed in WT OIR retina, suggesting increased oxidation of polyamines in OIR retina. These changes were minimal in A2-deficient OIR retina. Treatment using the polyamine oxidase inhibitor, N, N'-bis (2, 3-butadienyl)-1, 4-butanediamine dihydrochloride, significantly improved neuronal survival during OIR treatment. Our data suggest that retinal arginase is involved in the hyperoxia-induced neuronal degeneration in the OIR model, through the regulation of polyamine metabolism.

Inducible arginase 1 deficiency in mice leads to hyperargininemia and altered amino acid metabolism

Arginase deficiency is a rare autosomal recessive disorder resulting from a loss of the liver arginase isoform, arginase 1 (ARG1), which is the final step in the urea cycle for detoxifying ammonia. ARG1 deficiency leads to hyperargininemia, characterized by progressive neurological impairment, persistent growth retardation and infrequent episodes of hyperammonemia. Using the Cre/loxP-directed conditional gene knockout system, we generated an inducible Arg1-deficient mouse model by crossing “floxed” Arg1 mice with CreER^T2 mice. The resulting mice (Arg-Cre) die about two weeks after tamoxifen administration regardless of the starting age of inducing the knockout. These treated mice were nearly devoid of Arg1 mRNA, protein and liver arginase activity, and exhibited symptoms of hyperammonemia. Plasma amino acid analysis revealed pronounced hyperargininemia and significant alterations in amino acid and guanidino compound metabolism, including increased citrulline and guanidinoacetic acid. Despite no alteration in ornithine levels, concentrations of other amino acids such as proline and the branched-chain amino acids were reduced. In summary, we have generated and characterized an inducible Arg1-deficient mouse model exhibiting several pathologic manifestations of hyperargininemia. This model should prove useful for exploring potential treatment options of ARG1 deficiency.

[Advances in clinical and molecular genetics studies on argininemia]

Argininemia is a rare, autosomal recessive, metabolic disorder caused by an hereditary deficiency of hepatocytes arginase due to ARG1 gene defect. Arginase is the final enzyme in the urea cycle, catalyzing the hydrolysis of arginine to ornithine and urea. Research advances in the clinical manifestations, diagnosis, treatment, prenatal diagnosis and genetics of argininemia were reviewed in this paper. The clinical manifestations of patients with argininemia are complicated and nonspecific so that clinical diagnosis is usually difficult and delayed. Progressive spastic tetraplegia, seizures and cerebella atrophy are common clinical features of the disease. Blood amino acids analysis, arginase assay and ARG1 gene analysis are important to the diagnosis of argininemia. Early diagnosis and a protein-restricted diet with citrulline and benzoate supplements can contribute a lot to improve patient prognosis. With the application of liquid chromatography-tandem mass spectrometry in selective screening and newborn screening for inborn errors of metabolism, an ever-increasing number of patients with argininemia are detected at the asymptomatic or early stages.

Lethal phenotype in conditional late-onset arginase 1 deficiency in the mouse

Human arginase deficiency is characterized by hyperargininemia and infrequent episodes of hyperammonemia, which lead to neurological impairment with spasticity, loss of ambulation, seizures, and severe mental and growth retardation; uncommonly, patients suffer early death from this disorder. In a murine targeted knockout model, onset of the phenotypic abnormality is heralded by weight loss at around day 15, and death occurs typically by postnatal day 17 with hyperargininemia and markedly elevated ammonia. This discrepancy between the more attenuated juvenile-onset human disease and the lethal neonatal murine model has remained suboptimal for studying and developing therapy for the more common presentation of arginase deficiency. These investigations aimed to address this issue by creating an adult conditional knockout mouse to determine whether later onset of arginase deficiency also resulted in lethality. Animal survival and ammonia levels, body weight, circulating amino acids, and tissue arginase levels were examined as outcome parameters after widespread Cre-recombinase activation in a conditional knockout model of arginase 1 deficiency. One hundred percent of adult female and 70% of adult male mice died an average of 21.0 and 21.6 days, respectively, after the initiation of tamoxifen administration. Animals demonstrated elevated circulating ammonia and arginine at the onset of phenotypic abnormalities. In addition, brain and liver amino acids demonstrated abnormalities. These studies demonstrate that (a) the absence of arginase in adult animals results in a disease profile (leading to death) similar to that of the targeted knockout and (b) the phenotypic abnormalities seen in the juvenile-onset model are not exclusive to the age of the animal but instead to the biochemistry of the disorder. This adult model will be useful for developing gene- and cell-based therapies for this disorder that will not be limited by the small animal size of neonatal therapy and for developing a better understanding of the characteristics of hyperargininemia.

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.

Neonatal cholestasis: an uncommon presentation of hyperargininemia

Hyperargininemia is a rare inborn error of metabolism due to arginase deficiency, which is inherited in an autossomal recessive manner. Arginase is the final enzyme of the urea cycle and catalyzes the conversion of arginine to urea and ornithine. This condition typically presents in early childhood (between 2 and 4 years of age) with developmental delay associated with progressive spastic paraparesis. Neonatal presentation is very uncommon with a poorly described outcome. Here, we discuss two cases of neonatal cholestasis as initial clinical presentation of hyperargininemia. In case 1, diagnosis was established at 2 months of age upon investigation of the etiology of cholestatic injury pattern and hepatosplenomegaly, and treatment was then initiated at when the patient was 3 months old. Unfortunately, the patient had progressive biliary cirrhosis to end-stage liver disease complicated with portal hypertension for which she underwent successful orthotopic liver transplant at 7 years of age. In case 2, hyperargininemia was identified through newborn screening and treatment was started when patient was 21 days old. Cholestasis was only identified in the patient's further evaluation and it resolved 2 weeks into treatment. The patient is currently 18 months old and her development and neurological examination remain unremarkable. Neonatal cholestasis as first presentation of hyperargininemia is rare, but this disorder should be included in the differential diagnosis of unexplained cholestasis in the neonate. In fact, these two cases suggest that arginase deficiency may be the cause of cholestatic liver disease.

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.

Mouse model for human arginase deficiency

Deficiency of liver arginase (AI) causes hyperargininemia (OMIM 207800), a disorder characterized by progressive mental impairment, growth retardation, and spasticity and punctuated by sometimes fatal episodes of hyperammonemia. We constructed a knockout mouse strain carrying a nonfunctional AI gene by homologous recombination. Arginase AI knockout mice completely lacked liver arginase (AI) activity, exhibited severe symptoms of hyperammonemia, and died between postnatal days 10 and 14. During hyperammonemic crisis, plasma ammonia levels of these mice increased >10-fold compared to those for normal animals. Livers of AI-deficient animals showed hepatocyte abnormalities, including cell swelling and inclusions. Plasma amino acid analysis showed the mean arginine level in knockouts to be approximately fourfold greater than that for the wild type and threefold greater than that for heterozygotes; the mean proline level was approximately one-third and the ornithine level was one-half of the proline and ornithine levels, respectively, for wild-type or heterozygote mice--understandable biochemical consequences of arginase deficiency. Glutamic acid, citrulline, and histidine levels were about 1.5-fold higher than those seen in the phenotypically normal animals. Concentrations of the branched-chain amino acids valine, isoleucine, and leucine were 0.4 to 0.5 times the concentrations seen in phenotypically normal animals. In summary, the AI-deficient mouse duplicates several pathobiological aspects of the human condition and should prove to be a useful model for further study of the disease mechanism(s) and to explore treatment options, such as pharmaceutical administration of sodium phenylbutyrate and/or ornithine and development of gene therapy protocols.

Arginase expression in mouse embryonic development

We are using the model of the developing mouse embryo to elucidate the pattern of arginase expression in mammalian cells in normal animals and in arginase I (AI) deficiency during development by digoxigenin-labeled RNA in situ hybridization. Our goal is to understand the regulation of these isozymes, with the expectation that this knowledge will help patients suffering from AI deficiency. We found that AI mRNA was widely and strongly expressed in the normal developing mouse embryo; in contrast, a relatively strong AII mRNA signal was found only in the intestine. In the AI knockout mouse embryo, no AII overexpression was found. These results indicated that arginases are needed in mouse embryonic development and AI is the principal form required. The strong AI expression in the peripheral nervous system suggests that the pathogenesis of the neurological retardation in AI deficiency may be conditioned by AI deficiency in the nervous system during embryonic development.

Arginase deficiency

Hyperargininemia due to arginase deficiency is a rare, inherited, urea cycle disorder. We report a case of arginase deficiency in a 5-year old boy presenting with mild hyperammonemia, hyperargininemia, and dibasic aminoaciduria.