Newborn screening for hyperargininemia due to arginase 1 deficiency

Newborn screening for neuro-metabolic disorders: Strategies, clinical benefits, and prerequisites for program expansion

Newborn screening (NBS) is a successful program of secondary prevention for rare diseases, such as neuro-metabolic diseases, enabling early identification of affected individuals and pre-symptomatic treatment. Driven by innovations in high-throughput sequencing technologies, NBS panels have continued to grow and will probably be extended further in the future. However, implementing NBS for a disease is subject to various preconditions to maximize the benefit for the affected children, while avoiding harm to the screened healthy cohort, their families and the society. Ideally, data on clinical long-term benefit of NBS and early treatment is collected prior to NBS implementation through long-term observational studies and registries. In addition, NBS should be implemented as an iteratively evaluated public health program and the data collection should be accompanied by intra-operable long-term observational studies, ideally extended in international cooperations. In this review, the current expertise in NBS, the screening strategies and possible long-term clinical benefits are presented and discussed for several neuro-metabolic diseases, including propionic acidemia and isolated methylmalonic acidemias, homocystinurias, remethylation defects, acquired cobalamin (vitamin B12) deficiency, urea cycle disorders, tetrahydrobiopterin (BH4) and primary neurotransmitter disorders, as well as lysosomal storage disorders. Given these prerequisites, several of the neuro-metabolic diseases discussed here might be part of future NBS programs worldwide.

Therapeutic potential of natural arginase modulators: mechanisms, challenges, and future directions

Arginase (Arg) plays a pivotal role in numerous pathological processes, with its dysregulated expression being intricately associated with tumor progression and immune evasion. This review comprehensively examines the diversity, mechanisms, and clinical potential of natural Arg modulators, encompassing polyphenols, flavonoids, and terpenoids. These bioactive compounds exert their modulatory effects on Arg activity through multiple mechanisms, including direct enzyme interaction, regulation of signaling pathways, and modulation of cellular metabolism. The therapeutic potential of these metabolites spans across various medical domains, notably in cardiovascular diseases, oncology, neurological disorders, and inflammatory conditions. Specifically, polyphenol metabolites such as resveratrol and curcumin have demonstrated significant benefits in cardiovascular health and neuroprotection, while flavonoids including rutin and quercetin have shown promising effects on intracellular inflammatory factors and tumor cell proliferation. Similarly, terpenoids like perillyl alcohol and triptolide have been found to influence cell polarization processes. However, despite their substantial therapeutic potential demonstrated in experimental studies, the development of natural Arg modulators faces several significant challenges. These include complexities in drug design attributed to the intricate structure and multiple isoforms of Arg, difficulties in elucidating precise mechanisms due to Arg's multifaceted roles in various metabolic pathways, and limitations in current drug delivery systems. To overcome these challenges, future research should focus on continuous optimization of experimental design paradigms, enhancement of experimental models and data quality, thorough evaluation of therapeutic efficacy, and strategic integration of natural Arg modulators with precision medicine approaches.

Arginase 1 deficiency: a treatable form of spastic paraplegia

BACKGROUND

Arginase 1 deficiency (ARG1-D) is a rare hereditary urea cycle disorder characterized by elevated arginine levels, resulting in progressive neurological impairment and severe physical and cognitive disability. Due to its low prevalence, overlapping symptoms with other neurological disorders, and current limitations in newborn screening tools, ARG1-D is often misdiagnosed or diagnosed late, limiting access to early interventions.

AIM

This review and expert opinion aim to provide an overview of the clinical manifestations, diagnostic challenges, and treatment options for ARG1-D, offering a practical resource for specialists to recognize this rare, progressive, yet treatable disease.

RESULTS

ARG1-D typically presents with progressive spastic paraplegia, developmental delays, cognitive impairment, and seizures, with symptom onset and severity varying by age. Differential diagnoses mainly include hereditary spastic paraplegia, cerebral palsy, and hyperornithinemia-hyperammonemia-homocitrullinuria syndrome, each with distinct clinical features and biochemical markers. Potential red flags for ARG1-D include elevated plasma arginine levels, spasticity, seizures, and cognitive impairment. These should prompt further examinations to confirm the diagnosis, which is based on biochemical assays for hyperargininemia and on genetic testing. Once confirmed, early treatment is advised, including dietary protein restriction, ammonia scavengers, antiepileptic drugs, and novel therapies, such as pegzilarginase, which targets the disease's metabolic root.

CONCLUSION

Experts stress the importance of increased awareness of ARG1-D characteristics, noting that early recognition and treatment are crucial to patient outcomes. Greater recognition of ARG1-D's distinctive features, differential diagnosis, and diagnostic tools, even among non-specialist clinicians, could help prevent misdiagnoses and facilitate the identification of this rare yet treatable condition.

Understanding the Natural History and the Effects of Current Therapeutic Strategies on Urea Cycle Disorders: Insights from the UCD Spanish Registry

Background/Objectives: The present study updates the Spanish registry of patients with urea cycle disorders (UCD), originally established in 2013, to provide comprehensive epidemiological data and evaluate the impact of therapeutic strategies and newborn screening (NBS) on clinical outcomes. Methods: This retrospective, multicenter study focuses on 255 Spanish UCD patients. It includes all living and deceased cases up to February 2024, analyzing demographic, clinical, and biochemical variables. Results: The incidence of UCD in Spain over the past decade was 1:36,063 births. The most common defects were ornithine transcarbamylase deficiency (OTCD) and argininosuccinate synthetase deficiency. Early-onset (EO) cases comprised 32.7%, and 10.6% were diagnosed through NBS. Global mortality was 14.9%, higher in carbamoylphosphate synthetase 1 deficiency (36.8%) and male OTCD patients (32.1%) compared to other defects (p = 0.013). EO cases presented a higher mortality rate (35.8%) than late-onset (LO) cases (7.1%) (p < 0.0001). The median ammonia level in deceased patients was higher at 1058 µmol/L (IQR 410-1793) than in survivors at 294 µmol/L (IQR 71-494) (p < 0.0001). Diagnosis through NBS improved survival and reduced neurological impairment compared to symptomatic diagnosis. Neurological impairment occurred in 44% of patients, with worse neurological outcomes observed in patients with argininosuccinate lyase deficiency, arginase 1 deficiency, hyperornithinemia-hyperammonemia-homocitrullinuria, EO presentations, pre-2014 diagnosis, and patients with higher levels of ammonia at diagnosis. Among transplanted patients (20.6%), survival was 95.2%, with no significant neurological differences compared to non-transplanted patients. Conclusions: This updated analysis highlights the positive impact of NBS and advanced treatments on mortality and neurologic outcomes. Persistent neurological challenges underscore the need for further therapeutic strategies.

The correlation between vitamin D3 and arginine metabolism levels in newborns with amino acid metabolism disorders

This study aimed to explore the correlation between vitamin D3 and arginine (Arg) metabolism indicators in newborns with amino acid metabolism disorders. Based on clinical data, 30 newborns with amino acid metabolism diseases admitted to Shijiazhuang Fourth Hospital from June 2021 to June 2022 were selected as the disease group, and 30 healthy newborns from the same period were selected as the healthy group. After enrollment, blood samples were collected to measure the levels of Arg, Glycine (Gly), and vitamin D3 levels. The levels of Arg metabolism indicators and vitamin D3 levels in the 2 groups and the correlation between vitamin D3 levels and Arg metabolism indicators in the affected group were analyzed. The Arg level in the diseased group was higher than that in the healthy group, whereas the Gly and vitamin D3 levels were lower than those in the healthy group (P < .05). There was a significant negative correlation between vitamin D3 and Arg levels in the affected group, and a significant positive correlation with Gly levels (P < .05). Newborns with amino acid metabolism disorders have abnormally high Arg levels, significantly reduced Gly levels, and significantly decreased vitamin D3 levels. The degree of decline was closely related to the levels of indicators of Arg metabolism. Vitamin D3 supplementation can improve the Arg metabolism status of newborns with amino acid metabolism disorders.

ACMG/AMP variant classification framework in arginase 1 deficiency: Implications for birth prevalence estimates and diagnostics

Purpose

Arginase 1 (ARG1) deficiency manifests with hyperargininemia and progressive neurological impairment. Recent estimates of birth prevalence using allele frequencies of ARG1 variants do not sufficiently distinguish benign from pathogenic variants. Additionally, ongoing discussions of reproductive carrier screening for diseases such as ARG1 creates a need for improved understanding of ARG1 variant classification. Here, we incorporate American College of Medical Genetics and Genomics/Association for Molecular Pathology-developed guidelines for interpreting gene variants and in silico predictions to select allele frequencies for estimation of global birth prevalence of ARG1 deficiency.

Methods

We interrogated Genome Aggregation Database and PubMed for published (defined as identified in patients with clinically defined arginase deficiency in scientific literature, n = 73) and unpublished ARG1 variants (defined as variants present in Genome Aggregation Database, unique to ARG1, but not yet associated with clinical arginase deficiency, n = 302). American College of Medical Genetics and Genomics/Association for Molecular Pathology guidelines were applied to classify variants using Franklin Genoox artificial intelligence-powered platform and manual review.

Results

Of 73 published ARG1 variants, 16 classified as pathogenic, 30 as likely pathogenic, and 27 as variant of uncertain significance. Of 302 unpublished ARG1 variants, 3 classified as pathogenic, 28 likely pathogenic, and 229 variant of uncertain significance. Mutant allele frequency estimates ranged from 17 to 266 per 100,000 and birth prevalence from 1 in 141,331 to 34,602,076.

Conclusion

We show that a large proportion of ARG1 variants lack adequate evidence of pathogenicity. These findings underscore the significance of functional studies and accumulating clinical data for determination of variant pathogenicity and for improved understanding of global birth prevalence of ARG1 deficiency.

Societal costs and quality of life associated with arginase 1 deficiency in a European setting - a multinational, cross-sectional survey

BACKGROUND AND AIMS

Arginase 1 deficiency (ARG1-D) is a ultrarare disease with manifestations that cause mobility and cognitive impairment that progress over time and may lead to early mortality. Diseases such as ARG1-D have a major impact also outside of the health care sector and the aim of this study was to estimate the current burden of disease associated with ARG1-D from a societal perspective.

METHODS

The study was performed as a web-based survey of patients with ARG1-D and their caregivers in four European countries (France, Portugal, Spain, United Kingdom). The survey was distributed at participating clinics and included questions on e.g. symptoms (including the Gross Motor Function Classification System, GMFCS, and cognitive impairment), health care use, medication, ability to work, caregiving, and impact on health-related quality-of-life (HRQoL) using the EQ-5D-5L.

RESULTS

The estimated total mean societal cost per patient and year was £63,775 (SD: £49,944). The cost varied significantly with both mobility impairment (from £49,809 for GMFCS level 1 to £103,639 for GMFCS levels 3-5) and cognitive impairment (from £43,860 for mild level to £99,162 for severe level). The mean utility score on the EQ-5D-5L for patients was 0.498 (SD: 0.352). The utility score also varied significantly with both mobility impairment (from 0.783 for GMFCS level 1 to 0.153 for GMFCS level 3-5) and cognitive impairment (from 0.738 for mild level to 0.364 for severe level).

CONCLUSIONS

Similar to other studies of rare diseases, the study is based on a limited number of observations. However, the sample appear to be reasonably representative when comparing to previous studies of ARG1-D. This study shows that ARG1-D is associated with a high societal cost and significant impact on HRQoL. Earlier diagnosis and better treatment options that can postpone or withhold progression may therefore have a potential for improved HRQoL and savings for the patient, caregiver, and society.

Ammonium nanochelators in conjunction with arginine-specific enzymes in amperometric biosensors for arginine assay

Amino acid L-arginine (Arg), usually presented in food products and biological liquids, can serve both as a useful indicator of food quality and an important biomarker in medicine. The biosensors based on Arg-selective enzymes are the most promising devices for Arg assay. In this research, three types of amperometric biosensors have been fabricated. They exploit arginine oxidase (ArgO), recombinant arginase I (ARG)/urease, and arginine deiminase (ADI) coupled with the ammonium-chelating redox-active nanoparticles. Cadmium-copper nanoparticles (nCdCu) as the most effective nanochelators were used for the development of ammonium chemosensors and enzyme-coupled Arg biosensors. The fabricated enzyme/nCdCu-containing bioelectrodes show wide linear ranges (up to 200 µM), satisfactory storage stabilities (14 days), and high sensitivities (A⋅M-1⋅m-2) to Arg: 1650, 1700, and 4500 for ADI-, ArgO- and ARG/urease-based sensors, respectively. All biosensors have been exploited to estimate Arg content in commercial juices. The obtained data correlate well with the values obtained by the reference method. A hypothetic scheme for mechanism of action of ammonium nanochelators in electron transfer reaction on the arginine-sensing electrodes has been proposed.

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.

Arginase 1 Deficiency in Patients Initially Diagnosed with Hereditary Spastic Paraplegia

Background

Arginase 1 Deficiency (ARG1-D) is a rare autosomal recessive urea cycle disorder (UCD) characterized by pathologic elevation of plasma arginine and debilitating manifestations. Based on clinical commonalities and low disease awareness, ARG1-D can be diagnosed as hereditary spastic paraplegia (HSP), leading to treatment delays.

Cases

A Hispanic woman with unremarkable medical history experienced progressive lower-limb spasticity in her 20s and received a diagnosis of HSP. She developed significant gait abnormalities and is unable to walk without assistance. More recently, two Hispanic brothers with childhood-onset manifestations including lower-limb spasticity, developmental delays, and seizures presented with suspected HSP. All three patients were ultimately diagnosed with ARG1-D based on plasma arginine several-fold above normal levels and loss-of-function ARG1 variants. Disease progression occurred before ARG1-D was correctly diagnosed.

Literature Review

Retrospective analyses demonstrate that diagnostic delays in ARG1-D are common and can be lengthy. Because of clinical similarities between ARG1-D and HSP, such as insidious onset and progressive spasticity, accurate diagnosis of ARG1-D is challenging. Timely ARG1-D diagnosis is critical because this UCD is a treatable genetic cause of progressive lower-limb spasticity.

Conclusions

Arginase 1 Deficiency should be considered in HSP differential diagnosis until biochemically/genetically excluded, and should be routinely included in HSP gene panels.

Natural history of arginase 1 deficiency and the unmet needs of patients: A systematic review of case reports

Background

Arginase 1 deficiency (ARG1-D) is a rare, progressive and debilitating urea cycle disorder characterized by clinical manifestations including spasticity, seizures, developmental delay, and intellectual disability. The aim of this systematic review was to identify and summarize the natural history of ARG1-D and the unmet needs of patients.

Methods

A comprehensive search of published case reports was undertaken to identify patients with ARG1-D regardless of interventions, comparisons, or outcomes. MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, and other evidence-based medicine literature databases were searched on 20 April 2020. Quality was assessed using the Joanna Briggs Institute (JBI) Critical Appraisal Checklist. (PROSPERO registration: CRD42020212142.).

Results

One hundred and fifty seven ARG1-D patients were included from 111 publications (good overall quality based on JBI's Checklist); 84 (53.5%) were males. Motor deficits (including spasticity), intellectual disability, and seizures were reported in >50% of the cases. Mean age (SD) at diagnosis was 6.4 years and the laboratory findings most commonly reported to support diagnosis included elevated plasma arginine (81.5%), mutation in ARG1 gene through genetic testing (60%), and absence/reduction of red blood cell arginase activity (51%). Reported management approaches mainly included dietary protein restriction (68%), nitrogen scavengers (45%), and essential amino acid supplements (21%). Author-reported clinical improvement was documented for 26% of patients, 15% deteriorated, and 19% had limited or no change; notably, no indication of clinical outcome was reported for 40% cases.

Conclusion

This review illustrates a significant burden of disease and highlights a considerable unmet need for clinically effective treatment options for patients with ARG1-D.

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.

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.

Health care resource utilization in the management of patients with Arginase 1 Deficiency in the US: a retrospective, observational, claims database study

BACKGROUND

Arginase 1 Deficiency (ARG1-D) is an inherited metabolic disease that leads to significant morbidity.

AIMS

Despite the recognized burden of disease, information on health care resource utilization (HCRU) among patients with ARG1-D is lacking. We, therefore, sought to evaluate HCRU in ARG1-D relative to non-ARG1-D cohort.

MATERIALS AND METHODS

Patients with ≥2 ICD-10-CM diagnosis codes for ARG1-D were identified (first diagnosis code = index date) using professional fee claims linked with prescription claims. Patients with ARG1-D were matched 1:1 to a comparator cohort of patients with other medical conditions. Matching variables included age, sex, index year, payer type (Medicare, Medicaid, third party) and geographic region.

RESULTS

A total of 77 patients met the inclusion criteria for the ARG1-D cohort, with a median age of 15 years, 52% <18 years, and 52% male. Several concurrent diagnoses were recorded at a higher frequency in the ARG1-D cohort versus the matched comparator (spasticity 7 times higher; developmental delay ∼2 times higher; intellectual disability 5 times higher; and seizures 8 times higher). Emergency room visits occurred twice as often, laboratory tests were performed 1.5 times more often, hospitalization was required 3 times more often, and mean length of stay was longer for patients with ARG1-D than the comparator cohort (2.4 days vs. 0.3 days).

LIMITATIONS

A relatively short study period while the burden of ARG1-D increases over a lifetime due to disease progression.

CONCLUSIONS

Patients with ARG1-D had significantly greater HCRU compared with those without the disease; they presented with a more extensive comorbidity profile, accessed the health care system more frequently, required more intense monitoring and management, and had more frequent and longer hospitalizations relative to the comparator group. These findings demonstrate a high health burden in ARG1-D that is not mitigated by standard-of-care measures and emphasize the need for improved treatment options.

Hyperargininemia Due to Arginase 1 Deficiency: Variability in Clinical and Biochemical Presentations in Malaysian children

Objective

Hyperargininemia due to Arginase 1 deficiency is a rare inborn error of the urea cycle with an incidence estimated at 1:950 000. It has typical severe and progressive abnormal neurological features with biochemical findings of hyperargininemia and hyperexcretion of orotic acid. The aim of our study is to review the clinical and biochemical presentations of 4 children diagnosed with Arginase 1 deficiency in Malaysia and compare with the literature review.

Design and Methods

We retrospectively reviewed the medical records of 4 patients with molecularly confirmed Arginase 1 deficiency. Patients were identified from a selective high-risk screening of 51 682 symptomatic patients from January 2006 to December 2020.

Results

Our patients exhibited heterogeneous clinical presentations with acute and progressive neurological abnormalities and varying degrees of plasma arginine and urine orotic acid excretions. Interestingly, an unusual hyperexcretion of homocitrulline was found in 3 patients.

Conclusions

Hyperargininemia due to Arginase 1 deficiency can present acutely and hyperexcretion of homocitrulline can be an additional biochemical feature of Arginase 1 deficiency.

Current status of surviving patients with arginase 1 deficiency in Japan

Arginase 1 (ARG1) deficiency is a rare urea cycle disorder (UCD), with an estimated frequency of 1 per 2,200,000 births in Japan. Patients with ARG1 deficiency develop symptoms in late infancy or pre-school age with progressive neurological manifestations and sometimes present with severe hepatic disease. We previously investigated the status of UCDs in Japan; however, only one patient was identified as having ARG1 deficiency. Therefore, we aimed to investigate the current status of patients with ARG1 deficiency in 2018–2021 because almost 10 years have passed since the previous study. We present the disease history, clinical outcome, and treatment of five surviving patients with ARG1 deficiency and discuss the features of ARG1 deficiency in Japan. We found that clinicians often face difficulty in diagnosing ARG1 deficiency at the early stage of onset because of interpatient variability in onset time and clinical manifestations. Blood L-arginine and guanidino compounds were considered to be the major factors causing adverse neurodevelopmental outcomes. Therefore, early detection and intervention of ARG1 deficiency is essential for improved neurodevelopmental outcomes. Liver transplantation has been considered an effective treatment option that can dramatically improve the quality of life of patients, prior to the neurological manifestation of symptoms caused by ARG1 deficiency.

Direct detection of inorganic ions and underivatized amino acids in seconds using high-speed capillary electrophoresis coupled with back-scatter interferometry

High speed capillary electrophoresis (HSCE) combined with refractive index (RI) detection is developed for the rapid separation and detection of inorganic ions and amino acids. A mixture of three inorganic ions (K⁺, Na⁺, Li⁺) and eight amino acids (Lys, Arg, Ala, Gly, Val, Thr, Trp, Asp) are detected using back scatter interferometry (BSI), without the need for chemical modifications or contrast. A thin-walled separation capillary (50 μm i.d. by 80 μm o.d.) helps mitigate Joule heating at the high field strengths required for rapid separations. This, combined with a short 8 cm length-to-detector (10 cm total length), enables separations on the seconds time scale. Using a background electrolyte (BGE) of 4 M acetic acid (pH 1.6) and a field strength of 900 V cm^-1, all 11 analytes are separated in less than 40 s. Moreover, peaks in the BSI signal arising from the sample injection and EOF, enable electrophoretic mobilities to readily be obtained from apparent mobilities. This leads to excellent repeatability, with analyte electrophoretic mobilities varying from 0.39 to 1.56 % RSD over eight consecutive separations. The universal detection of inorganic ions and amino acids without prior chemical modification or additives in the BGE is an advantage of refractive index detection. A disadvantage arises from modest detection limits. Here, however, we show that submicromolar detection is possible with careful thermostatting of the thin separation capillary. A series of electropherograms are used to quantify arginine concentrations from 700 nM to 500 μM, using 50 μM Li⁺ as an internal standard. The resulting calibration curve leads to a calculated LOD of 376 nM and a LOQ of 1.76 μM. Diagnostically relevant amino acid panels are also separated, illustrating the potential for future applications in neurodegenerative and metabolic disease diagnostics. HSCE combined with BSI detection, therefore, is shown to be a rapid, sensitive, and universal approach for analyzing sample mixtures.

Arginine to ornithine ratio as a diagnostic marker in patients with positive newborn screening for hyperargininemia

Arginase deficiency is a rare inborn error of metabolism that interrupts the final step of the urea cycle. Untreated individuals often present with episodic hyperammonemia, developmental delay, cognitive impairment, and spasticity in early childhood. The newborn screening (NBS) algorithms for arginase deficiency vary between individual states in the US but often include hyperargininemia and elevated arginine to ornithine (Arg/Orn) ratio. Here, we report 14 arginase deficiency cases, including two patients with positive NBS for hyperargininemia in whom the diagnosis of arginase deficiency was delayed owing to normal or near normal plasma arginine levels on follow-up testing. To improve the detection capability for arginase deficiency, we evaluated plasma Arg/Orn ratio as a secondary diagnostic marker in positive NBS cases for hyperargininemia. We found that plasma Arg/Orn ratio combined with plasma arginine was a better marker than plasma arginine alone to differentiate patients with arginase deficiency from unaffected newborns. In fact, elevated plasma arginine in combination with an Arg/Orn ratio of ≥1.4 identified all 14 arginase deficiency cases. In addition, we examined the impact of age on plasma arginine and ornithine levels. Plasma arginine increased 0.94 μmol/L/day while ornithine was essentially unchanged in the first 31 days of life, which resulted in a similar increasing trend for the Arg/Orn ratio (0.01/day). This study demonstrated that plasma Arg/Orn ratio as a secondary diagnostic marker improved the detection capability for arginase deficiency in newborns with hyperargininemia, which will allow timely detection of arginase deficiency and hence initiation of treatment before developing symptoms.

Novel Homozygous Missense Mutation in the ARG1 Gene in a Large Sudanese Family

Background: Arginases catalyze the last step in the urea cycle. Hyperargininemia, a rare autosomal-recessive disorder of the urea cycle, presents after the first year of age with regression of milestones and evolves gradually into progressive spastic quadriplegia and cognitive dysfunction. Genetic studies reported various mutations in the ARG1 gene that resulted in hyperargininemia due to a complete or partial loss of arginase activity.

Case Presentation: Five patients from an extended highly consanguineous Sudanese family presented with regression of the acquired milestones, spastic quadriplegia, and mental retardation. The disease onset ranged from 1 to 3 years of age. Two patients had epileptic seizures and one patient had stereotypic clapping. Genetic testing using whole-exome sequencing, done for the patients and a healthy parent, confirmed the presence of a homozygous novel missense variant in the ARG1 gene [GRCh37 (NM_001244438.1): exon 4: g.131902487T>A, c.458T>A, p.(Val153Glu)]. The variant was predicted pathogenic by five algorithms and affected a highly conserved amino acid located in the protein domain ureohydrolase, arginase subgroup. Sanger sequencing of 13 sampled family members revealed complete co-segregation between the variant and the disease distribution in the family in line with an autosomal-recessive mode of inheritance. Biochemical analysis confirmed hyperargininemia in five patients.

Conclusion: This study reports the first Sudanese family with ARG1 mutation. The reported variant is a loss-of-function missense mutation. Its pathogenicity is strongly supported by the clinical phenotype, the computational functional impact prediction, the complete co-segregation with the disease, and the biochemical assessment.

Metabolic Serendipities of Expanded Newborn Screening

Incidental findings on newborn screening (NBS) are results that are not the target of screening within a given NBS program, but rather are found as a result of the screening and resulting diagnostic workup for that target. These findings may not have an immediate clinical impact on the newborn, but are sometimes an additional benefit of NBS programs and may be considered secondary targets of NBS programs. This work describes four case reports that had incidental findings on the NBS, which eventually led to the diagnosis of another metabolic disease instead of the one that was initially suspected. The first case was a new defect in the cationic amino acid transporter-2 (CAT-2), which was oriented as an arginase-1 deficiency in the newborn. The second case was a maternal glutaric aciduria type 1 (GA-1) that mimicked a carnitine transporter deficiency in the newborn. The third report was a case of lysinuric protein intolerance (LPI), which appeared as high levels of citrulline on the NBS. The fourth case was a mother with homocystinuria that was diagnosed during the biochemical study of vitamin B₁₂ status. All cases provide new or interesting data that will help guide differential diagnosis in the future.

Lipid nanoparticle-targeted mRNA therapy as a treatment for the inherited metabolic liver disorder arginase deficiency

Arginase deficiency is caused by biallelic mutations in arginase 1 (ARG1), the final step of the urea cycle, and results biochemically in hyperargininemia and the presence of guanidino compounds, while it is clinically notable for developmental delays, spastic diplegia, psychomotor function loss, and (uncommonly) death. There is currently no completely effective medical treatment available. While preclinical strategies have been demonstrated, disadvantages with viral-based episomal-expressing gene therapy vectors include the risk of insertional mutagenesis and limited efficacy due to hepatocellular division. Recent advances in messenger RNA (mRNA) codon optimization, synthesis, and encapsulation within biodegradable liver-targeted lipid nanoparticles (LNPs) have potentially enabled a new generation of safer, albeit temporary, treatments to restore liver metabolic function in patients with urea cycle disorders, including ARG1 deficiency. In this study, we applied such technologies to successfully treat an ARG1-deficient murine model. Mice were administered LNPs encapsulating human codon-optimized ARG1 mRNA every 3 d. Mice demonstrated 100% survival with no signs of hyperammonemia or weight loss to beyond 11 wk, compared with controls that perished by day 22. Plasma ammonia, arginine, and glutamine demonstrated good control without elevation of guanidinoacetic acid, a guanidino compound. Evidence of urea cycle activity restoration was demonstrated by the ability to fully metabolize an ammonium challenge and by achieving near-normal ureagenesis; liver arginase activity achieved 54% of wild type. Biochemical and microscopic data showed no evidence of hepatotoxicity. These results suggest that delivery of ARG1 mRNA by liver-targeted nanoparticles may be a viable gene-based therapeutic for the treatment of arginase deficiency.

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.

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.