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.

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.

Arginase I mRNA therapy - a novel approach to rescue arginase 1 enzyme deficiency.

Arginase I (ARG1) deficiency is an autosomal recessive urea cycle disorder, caused by deficiency of the enzyme Arginase I, resulting in accumulation of arginine in blood. Current Standard of Care (SOC) for ARG1 deficiency in patients or those having detrimental mutations of ARG1 gene is diet control. Despite diet and drug therapy with nitrogen scavengers, ~25% of patients suffer from severe mental deficits and loss of ambulation. 75% of patients whose symptoms can be managed through diet therapy continue to suffer neuro-cognitive deficits. In our research, we demonstrate in vitro and in vivo that administration of ARG1 mRNA increased ARG1 protein expression and specific activity in relevant cell types, including ARG1-deficient patient cell lines, as well as in wild type mice for up to 4 days. These studies demonstrate that ARG1 mRNA treatment led to increased functional protein expression of ARG1 and subsequently an increase in urea. Hence, ARG1 mRNA therapy could be a potential treatment option to develop for patients.

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.

[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.

Advances in clinical and molecular genetics studies on argininemia / 中国当代儿科杂志

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.

High plasma citrulline and arginine levels ensured by sustained-release citrulline supplementation in rats.

OBJECTIVE: Dietary-supplemented arginine has been shown to have positive effects on cardiovascular disease, but several drawbacks exist and could potentially be avoided by using L-citrulline, since it is recycled to L-arginine. However, citrulline is very rapidly metabolized. We therefore developed a sustained-release form of citrulline and evaluated its metabolic behavior in rats. METHODS: Male Sprague Dawley rats were divided into three groups: receiving "empty microcapsule" (control group), 1 g/kg/d immediate-release citrulline (IR citrulline group), or 1 g/kg/d sustained-release citrulline (SR citrulline group). Citrulline was given each day at 9 a.m. after blood samples for 9 d, and on day 10, blood samples were drawn every 4 h to study the decrease in plasma amino acid concentrations. RESULTS: SR citrulline led to a sustained increase in citrullinemia and argininemia compared to IR citrulline, and on day 6 argininemia was significantly (P < 0.01) higher with SR compared to IR citrulline. Moreover, argininemia was significantly higher in the SR citrulline group than in controls throughout the study and SR citrulline maintained high argininemia and citrullinemia, at least over 12 h. CONCLUSION: This experimental study provides a strong rationale for using this new formulation for atherosclerosis treatment.

Infection with arginase-deficient Leishmania major reveals a parasite number-dependent and cytokine-independent regulation of host cellular arginase activity and disease pathogenesis.

The balance between the products of L-arginine metabolism in macrophages regulates the outcome of Leishmania major infection. L-arginine can be oxidized by host inducible NO synthase to produce NO, which contributes to parasite killing. In contrast, L-arginine hydrolysis by host arginase blocks NO generation and provides polyamines, which can support parasite proliferation. Additionally, Leishmania encode their own arginase which has considerable potential to modulate infectivity and disease pathogenesis. In this study, we compared the infectivity and impact on host cellular immune response in vitro and in vivo of wild-type (WT) L. major with that of a parasite arginase null mutant (arg(-)) L. major. We found that arg(-) L. major are impaired in their macrophage infectivity in vitro independent of host inducible NO synthase activities. As with in vitro results, the proliferation of arg(-) L. major in animal infections was also significantly impaired in vivo, resulting in delayed onset of lesion development, attenuated pathology, and low parasite burden. Despite this attenuated pathology, the production of cytokines by cells from the draining lymph node of mice infected with WT and arg(-) L. major was similar at all times tested. Interestingly, in vitro and in vivo arginase levels were significantly lower in arg(-) than in WT-infected cases and were directly correlated with parasite numbers inside infected cells. These results suggest that Leishmania-encoded arginase enhances disease pathogenesis by augmenting host cellular arginase activities and that contrary to previous in vitro studies, the host cytokine response does not influence host arginase activity.

Guanidino compound analysis as a complementary diagnostic parameter for hyperargininemia: follow-up of guanidino compound levels during therapy.

The aim of this collaborative study was to investigate whether guanidino compound analyses in the biologic fluids can be used as a complementary diagnostic parameter for hyperargininemia. Guanidino compounds were determined in the biologic fluids of all known living hyperargininemic patients using a cation exchange chromatographic system with a fluorescence detection method. The serum arginine, homoarginine, alpha-keto-delta-guanidino-valeric acid, argininic acid, and N-alpha-acetylarginine levels of all the hyperargininemic patients are higher than the normal range. Similar increases were seen for the urinary excretion of alpha-keto-delta-guanidinovaleric acid and argininic acid. Untreated hyperargininemic patients have the highest guanidino compound levels in cerebrospinal fluid. However, even under therapy, the arginine, homoarginine, alpha-keto-delta-guanidinovaleric acid, and argininic acid levels in cerebrospinal fluid are still increased. Protein restriction alone is not sufficient to normalize the hyperargininemia, but protein restriction together with supplementation of essential amino acids with or without sodium benzoate decreases further the arginine levels. However, whereas the argininemia can be normalized, the catabolites of arginine are still increased. We conclude that the urinary amino acid levels may remain normal in hyperargininemia, whereas consistent increases of the guanidino compounds are observed. Thus, guanidino compound analyses can be used as a complementary biochemical diagnostic parameter for hyperargininemia. Although the argininemia can be normalized by therapy, the levels of the catabolites of arginine are still elevated.

Hyperammonemia.

A symptomatic elevation in plasma ammonium concentration, termed hyperammonemia, is associated with numerous congenital and acquired conditions (Table 11). In some cases, such as urea cycle disorders, ammonia is the principal toxin. In other instances, such as portal systemic encephalopathy, it is but one of a number of metabolic disturbances, However, in either case hyperammonemic episodes should be treated aggressively to prevent coma, subsequent brain damage, or death. This involves restricting protein intake, providing adequate calories, and giving agents that remove accumulated nitrogen. Long-term therapy relies on diagnosing the specific disease rate. This rarely requires invasive procedures such as liver biopsy. In most cases measurement of plasma amino acids and urinary organic acids will identify the defect. Treatment involving restriction of nitrogen intake, vitamin supplementation, or stimulation of alternative pathways of waste nitrogen excretion can then be instituted. Early therapy, especially in patients with neonatal-onset hyperammonemia, is imperative to avoid severe brain damage. On this basis, the plasma ammonium level should be determined in virtually every newborn with lethargy, hypotonia, poor feeding, seizures, and/or respiratory distress of unclear origin (Table 12).

Isoenzyme pattern and immunological properties of arginase in normal and hyperargininemia fibroblasts.

Arginase deficiency is an inborn error of the last step in the urea cycle and leads to profound hyperargininemia. The enzyme deficiency has been demonstrated in the liver and red blood cells. In cultured patient fibroblasts, the activity is normal. Arginase exists in multiple molecular forms only one of which is missing in hyperargininemic patients. In fibroblasts, three arginase isoenzymes can be demonstrated by DEAE-cellulose column chromatography, two by electrophoresis and by immunoprecipitation methods. From the present data, it is improbable that part of the A1 isoenzyme in fibroblasts originates from fetal calf serum arginase which supplements the culture media. None of the techniques for the separation and analyses of arginase isoenzyme allows to differentiate between the normal and the arginase-deficient phenotype. A possible explanation would be that the defect in A1 arginase observed in the liver is the result of a regulatory defect.