Are asymptomatic carriers of OTC deficiency always asymptomatic? A multicentric retrospective study of risk using the UCDC longitudinal study database

BACKGROUND

Ornithine transcarbamylase deficiency (OTCD) due to an X-linked OTC mutation, is responsible for moderate to severe hyperammonemia (HA) with substantial morbidity and mortality. About 80% of females with OTCD remain apparently "asymptomatic" with limited studies of their clinical characteristics and long-term health vulnerabilities. Multimodal neuroimaging studies and executive function testing have shown that asymptomatic females exhibit limitations when stressed to perform at higher cognitive load and had reduced activation of the prefrontal cortex. This retrospective study aims to improve understanding of factors that might predict development of defined complications and serious illness in apparent asymptomatic females. A proband and her daughter are presented to highlight the utility of multimodal neuroimaging studies and to underscore that asymptomatic females with OTCD are not always asymptomatic.

METHODS

We review data from 302 heterozygote females with OTCD enrolled in the Urea Cycle Disorders Consortium (UCDC) longitudinal natural history database. We apply multiple neuroimaging modalities in the workup of a proband and her daughter.

RESULTS

Among the females in the database, 143 were noted as symptomatic at baseline (Sym). We focused on females who were asymptomatic (Asx, n = 111) and those who were asymptomatic initially upon enrollment in study but who later became symptomatic sometime during follow-up (Asx/Sym, n = 22). The majority of Asx (86%) and Asx/Sym (75%) subjects did not restrict protein at baseline, and ~38% of Asx and 33% of Asx/Sym subjects suffered from mild to severe neuropsychiatric conditions such as mood disorder and sleep problems. The risk of mild to severe HA sometime later in life for the Asx and Asx/Sym subjects as a combined group was ~4% (5/133), with ammonia ranging from 77 to 470 μM and at least half (2/4) of subjects requiring hospital admission and nitrogen scavenger therapy. For this combined group, the median age of first HA crisis was 50 years, whereas the median age of first symptom which included neuropsychiatric and/or behavioral symptoms was 17 years. The multimodal neuroimaging studies in female heterozygotes with OTCD also underscore that asymptomatic female heterozygotes with OTCD (e.g., proband) are not always asymptomatic.

CONCLUSIONS

Analysis of Asx and Asx/Sym females with OTCD in this study suggests that future evidence-based management guidelines and/or a clinical risk score calculator for this cohort could be useful management tools to reduce morbidity and improve long-term quality of life.

Adult presentation of ornithine transcarbamylase deficiency: a possible cause of hyperammonemia after high-dose chemotherapy and stem cell transplantation

Hyperammonemia is a rare and often fatal complication following the conditioning therapy in autologous and allogeneic stem cell transplant recipients. It is characterized by anorexia, vomiting, lethargy and coma without any other apparent cause. The diagnosis is often delayed because symptoms can be subtle and ammonia is usually not included among the routine analyzes. Previous reports have not identified the molecular mechanisms behind hyperammonemia in stem cell transplant recipients. Urea cycle disorders (UCDs) are inborn errors of metabolism leading to hyperammonemia that usually presents in early childhood, whereas first presentation in adults is less common. Here we describe an adult woman with hyperammonemia following autologous stem cell transplantation for multiple myeloma. No apparent cause of hyperammonemia was identified, including portosystemic shunting, liver dysfunction or recent hyperammonemia-inducing chemotherapy. Hyperammonemia, normal blood glucose as well as anion gap and a previous history of two male newborns that died early after birth, prompted biochemical and genetic investigations for a UCD. A heterozygous variant in the X-linked gene encoding ornithine transcarbamylase (OTC) was identified and was regarded as a cause of UCD. The patient improved after treatment with nitrogen scavengers and high caloric intake according to a UCD protocol. This case report suggests that UCD should be considered as a possible cause of hyperammonemia following stem cell transplantation.

Hyperammonemia Encephalopathy due to Urea Cycle Disorder Precipitated by Gastrointestinal Bleed in the Setting of Prior Bariatric Surgery

The urea cycle is a metabolic pathway that excretes nitrogenous waste products from the body. Urea cycle disorders (UCDs) result from enzymatic deficiencies within this pathway, which can lead to life-threatening hyperammonemia. Gastric bypass-related hyperammonemia in patients who have undergone Roux-en-Y gastric bypass surgery has been previously reported. UCDs have been implicated as a cause of gastric bypass-related hyperammonemia. In this report, we present the case of a patient with a history of bariatric surgery who experienced severe hyperammonemia encephalopathy triggered by a gastrointestinal bleed due to an undiagnosed UCD.

Variant in the allosteric domain of CPS1 protein associated with effectiveness of N-carbamoyl glutamate therapy in neonatal onset CPS1 deficiency

OBJECTIVES

Carbamoyl phosphate synthetase 1 (CPS1) deficiency is a severe urea cycle disorder. Patients can present with hyperammonemic coma in the first days of life. Treatment includes nitrogen scavengers, reduced protein intake and supplementation with L-arginine and/or L-citrulline. N-carbamoyl glutamate (NCG) has been hypothesized to stimulate the residual CPS1 function, although only few patients are reported.

CASE PRESENTATION

We report a patient with neonatal-onset CPS1 deficiency who received NCG in association with nitrogen scavenger and L-citrulline. The patient carried the novel variants CPS1-c.2447A>G p.(Gln816Arg) and CPS1-c.4489T>C p.(Tyr1497His). The latter is localized in the C-terminal allosteric domain of the protein, and is implicated in the binding of the natural activator N-acetyl-L-glutamate. NCG therapy was effective in controlling ammonia levels, allowing to increase the protein intake.

CONCLUSIONS

Our data show that the response to NCG can be indicated based on the protein structure. We hypothesize that variants in the C-terminal domain may be responsive to NCG therapy.

Anesthetic Management of the Surgical Correction of Idiopathic Scoliosis in a Teenager With Ornithine Transcarbamalyse Deficiency

Ornithine transcarbamylase (OTC) deficiency is the most common genetic disorder of the urea cycle. These disorders are characterized by an inability to metabolize ammonia into urea, leading to hyperammonemia with variable physiological consequences and presenting important anesthetic challenges, especially the perioperative prevention of hyperammonemia and management of its consequences, should it occur. Idiopathic scoliosis (IS) is the most common spinal deformity requiring surgical treatment. This paper presents the case of a 16-year-old female with OTC deficiency who underwent spinal fusion for IS. The chosen anesthetic strategy was combined anesthesia with total intravenous general anesthesia using target-controlled infusion pumps, an erector spinae plane block (ESPB), and a multi-pronged approach to ensure metabolic control while avoiding hyperammonemia. The existing literature regarding major surgery in patients with OTC deficiency is sparse, and this paper provides one of the first case reports of a scoliosis correction surgery, as well as one of the first descriptions of prolonged propofol infusion and locoregional anesthesia with an erector spinae plane block in this context.

Breastfeeding and Inborn Errors of Amino Acid and Protein Metabolism: A Spreadsheet to Calculate Optimal Intake of Human Milk and Disease-Specific Formulas

Human milk (HM) offers important nutritional benefits. However, except for phenylketonuria (PKU), there are little data on optimal levels of consumption of HM and a special formula free of disease-related amino acids (SF-AA) in infants with inborn errors of metabolism of amino acids and proteins (IEM-AA-P). We designed a spreadsheet to calculate the amounts of SF-AA and HM required to cover amino acid, protein, and energy needs in patients with the nine main IEM-AA-P in infants aged under 6 months. Upon entering the infant's weight and the essential amino acid or intact protein requirements for the specific IEM, the spreadsheet calculates the corresponding required volume of HM based on the amino acid concentration in HM. Next, the theoretical daily fluid intake (typical range, 120-200 mL/kg/day) is entered, and the estimated daily fluid intake is calculated. The required daily volume of SF-AA is calculated as the difference between the total fluid intake value and the calculated volume of HM. The spreadsheet allows for the introduction of a range of requirements based on the patient's metabolic status, and includes the option to calculate the required volume of expressed HM, which may be necessary in certain conditions such as MMA/PA and UCD. In cases in which breastfeeding on demand is feasible, the spreadsheet determines the daily amount of SF-AA divided over 6-8 feeds, assuming that SF-AA is administered first, followed by HM as needed. Intake data calculated by the spreadsheet should be evaluated in conjunction with data from clinical and nutritional analyses, which provide a comprehensive understanding of the patient's nutritional status and help guide individualized dietary management for the specific IEM.

Functional identification of two novel variants and a hypomorphic variant in ASS1 from patients with Citrullinemia type I

Background: Citrullinemia type I (CTLN1) is a rare autosomal recessive inborn error of the urea cycle caused by mutations in the gene encoding the arginosuccinate synthetase (ASS1) enzyme. Classic CTLN1 often manifests with acute hyperammonemia and neurological symptoms. Molecular genetic testing is critical for patient diagnosis. Methods: Three unrelated families with clinically suspected CTLN1 were included in this study. Potential pathogenic variants were identified using whole exome sequencing (WES) and validated using Sanger sequencing. Western blotting, quantitative PCR, immunofluorescent staining, and ELISA were used to assess functional changes in candidate ASS1 variants. Results: Five variants were identified, two of which were novel, and one has been reported, but its pathogenicity was not validated. The novel variant c.649-651del (p.P217del) and the 5'UTR variant (c.-4C>T) resulted in a decrease in ASS1 expression at both the protein and transcription levels. The other novel variant, c.1048C>T (p.Q350*), showed a marked decrease in expression at the protein level, with the formation of truncated proteins but an increased transcription. Both c.649_651del (p.P217del) and c.1048C>T (p.Q350*) showed a highly significant reduction in enzyme activity, while c.-4C>T had no effect. Conclusion: We identified two novel variants and a hypomorphic non-coding variant in ASS1 and validated the pathogenicity using functional studies. Our findings contribute to expanding the spectrum of ASS1 variants and understanding the genotype-phenotype relationships of CTLN1.

The functional impact of 1,570 individual amino acid substitutions in human OTC

Deleterious mutations in the X-linked gene encoding ornithine transcarbamylase (OTC) cause the most common urea cycle disorder, OTC deficiency. This rare but highly actionable disease can present with severe neonatal onset in males or with later onset in either sex. Individuals with neonatal onset appear normal at birth but rapidly develop hyperammonemia, which can progress to cerebral edema, coma, and death, outcomes ameliorated by rapid diagnosis and treatment. Here, we develop a high-throughput functional assay for human OTC and individually measure the impact of 1,570 variants, 84% of all SNV-accessible missense mutations. Comparison to existing clinical significance calls, demonstrated that our assay distinguishes known benign from pathogenic variants and variants with neonatal onset from late-onset disease presentation. This functional stratification allowed us to identify score ranges corresponding to clinically relevant levels of impairment of OTC activity. Examining the results of our assay in the context of protein structure further allowed us to identify a 13 amino acid domain, the SMG loop, whose function appears to be required in human cells but not in yeast. Finally, inclusion of our data as PS3 evidence under the current ACMG guidelines, in a pilot reclassification of 34 variants with complete loss of activity, would change the classification of 22 from variants of unknown significance to clinically actionable likely pathogenic variants. These results illustrate how large-scale functional assays are especially powerful when applied to rare genetic diseases.

Rare Adult-onset Citrullinemia Type 1 in the Postpartum Period: A Case Report

INTRODUCTION

Citrullinemia type 1 (CTLN1) is a urea cycle disorder caused by defective argininosuccinate synthetase leading to impaired ammonia elimination. Urea cycle disorders are typically diagnosed on neonatal screening but rarely can lie dormant until a metabolic stressor causes initial onset of symptoms in adulthood.

CASE REPORT

A 23-year-old female presented four days postpartum to the emergency department (ED) obtunded and declined to the point of requiring intubation. Labs revealed hyperammonemia, and she was subsequently found to have CTLN1.

CONCLUSION

Urea cycle disorders presenting in adulthood are a rare etiology for the common ED complaint of altered mental status. The low incidence makes these treatable disorders easy to overlook leading to potentially significant morbidity and mortality. Therefore, it is important to recognize the risk factors that can trigger an acute metabolic derangement. This case highlights common risk factors for metabolic stress, possible presenting symptoms, and the positive outcome achievable when recognized and treated in a timely fashion.

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.

Novel pathogenic variant (c.2947C > T) of the carbamoyl phosphate synthetase 1 gene in neonatal-onset deficiency

Background

Carbamoyl phosphate synthetase 1 deficiency (CPS1D) is a rare autosomal recessive urea cycle disorder characterized by hyperammonaemia. The biochemical measurement of the intermediate metabolites is helpful for CPS1D diagnosis; it however cannot distinguish CPS1D from N-acetylglutamate synthetase deficiency. Therefore, next-generation sequencing (NGS) is often essential for the accurate diagnosis of CPS1D.

Methods

NGS was performed to identify candidate gene variants of CPS1D in a Asian neonatal patient presented with poor feeding, reduced activity, tachypnea, lethargy, and convulsions. The potential pathogenicity of the identified variants was predicted by various types of bioinformatical analyses, including evolution conservation, domain and 3D structure simulations.

Results

Compound heterozygosity of CPS1D were identified. One was in exon 24 with a novel heterozygous missense variant c.2947C > T (p.P983S), and another was previously reported in exon 20 with c.2548C > T (p.R850C). Both variants were predicted to be deleterious. Conservation analysis and structural modeling showed that the two substituted amino acids were highly evolutionarily conserved, resulting in potential decreases of the binding pocket stability and the partial loss of enzyme activity.

Conclusion

In this study, two pathogenic missense variants were identified with NGS, expanding the variants pectrum of the CPS1 gene. The variants and related structural knowledge of CPS enzyme demonstrate the applicability for the accurate diagnosis of CPS1D.

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.

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.

Nonhepatic Hyperammonemia With Septic Shock: Case and Review of Literature

Elevated ammonia levels lead to cerebral edema, encephalopathy, seizures, coma, and death. Hyperammonemia is primarily associated with liver disease; however, there are rare cases without liver disease. Noncirrhotic hyperammonemia is primarily due to increased production and/or decreased elimination of ammonia. We present a rare case of a 35-year-old female with severe acute noncirrhotic hyperammonemia associated with gram-negative septic shock and a suspected undiagnosed partial urea cycle enzyme deficiency. She had elevated blood and urine amino acid levels speculated to be due to an underlying urea cycle defect, which was unmasked in the setting of septic shock with urea splitting bacteria leading to severely elevated ammonia levels. Ammonia levels were rapidly corrected with hemodialysis, as other conventional treatments failed. We highlight the importance of considering noncirrhotic causes of hyperammonemia in patients with elevated ammonia levels and intact liver function. Prompt treatment should begin with reducing the catabolic state, nitrogen scavenging, replacing urea cycle substrates, decreasing intestinal absorption, and augmented removal of ammonia with renal replacement therapy.

Case Report: Juvenile Myelomonocytic Leukemia Underlying Ornithine Transcarbamylase Deficiency Safely Treated Using Hematopoietic Stem Cell Transplantation

BACKGROUND

Juvenile myelomonocytic leukemia (JMML), which is predominantly found in infants, is a clonal abnormality of pluripotent hematopoietic stem cells and presents with the symptoms of both myeloproliferative tumors and myelodysplastic syndromes. Estimates have shown that ~20 cases of JMML occur annually in Japan. Ornithine transcarbamylase deficiency (OTCD), the most common among all urea cycle disorders (UCDs), occurs in 1 of 80,000 people in Japan.

CASE PRESENTATION

A 10-month-old infant who had fever, vomiting, and diarrhea for 2 days was referred to our hospital for the following abnormalities in blood tests: white blood cell count, 48,200/μL; hemoglobin, 9.0 g/dL; and platelet count, 135,000/μL. Bone marrow examination showed a nucleated cell count of 396,000/mm³ and blast cell count of 5.0%, as well as decreased mature granulocyte count and slightly myeloperoxidase stain-negative blasts but no monoclonal cell proliferation on May-Giemsa staining. Colony assay showed the proliferation of spontaneous colony and high sensitivity to granulocyte-macrophage colony-stimulating factor. Genetic analysis of peripheral blood mononuclear cells showed that the patient was positive for neuroblastoma RAS (NRAS) mutation. The patient was ultimately diagnosed with JMML. Approximately 170 days after his first hematopoietic stem cell transplantation (HSCT), the patient's JMML relapsed. Shortly after the recurrence, nausea, vomiting, hyperventilation, and decreased vitality were observed, followed by a decrease in the level of consciousness. The patient's ammonia level was 472 μmol/L. A test for seven different genetic mutations for the UCD showed the presence of c. 119G>A (amino acid change p. Arg40His). As such, late-onset OTCD was added to his diagnosis. Administration of sodium phenylacetate, l-arginine hydrochloride, and carnitine was continued following the diagnosis of OTCD, after which hyperammonemia was not observed. Regarding JMML relapse, HSCT was performed on day 405 after the first transplantation.

CONCLUSION

Hyperammonemia should be considered a differential diagnosis when unexplained and non-specific symptoms occur during the treatment of hematologic malignancies. Patients should be tested for UCD as a cause of hyperammonemia, and treatment for hyperammonemia should be continued until the cause is identified. The patient shows normal developmental progress, has an intact neurological status, and has not experienced another hyperammonemia attack. His JMML has remained in remission for over 3 years.

Food Coma: Hyperammonemic Encephalopathy From Refeeding Syndrome

Hyperammonemic encephalopathy (HAE) from extrahepatic causes is increasingly being recognized. Refeeding syndrome is characterized by severe fluid and electrolyte shifts following the reintroduction of nutrition. We describe the case of a 67-year-old man with bilateral maxillary sinus squamous cell carcinoma on nivolumab who became comatose after initiation of enteral feeding. Initial workup was notable for severe hypophosphatemia (<1 mg/dL) and markedly elevated ammonia (226 µmol/L). Neuroimaging was unrevealing. Correction of hypophosphatemia did not improve mental status. Ammonia levels briefly decreased while holding enteral feeding but worsened again on resumption. High-volume continuous renal replacement therapy was recommended but deferred in accordance with family wishes. We hypothesize that HAE may have been precipitated by a combination of refeeding-induced high nitrogen burden and limited detoxification via the urea cycle and extrahepatic pathways in the setting of severe protein-energy malnutrition and underlying malignancy. Nivolumab could have contributed as well.

Characterization and Treatment Responsiveness of Genetically Engineered Ornithine Transcarbamylase-Deficient Pig

To develop novel medical technologies, pig disease models are invaluable especially in the final stages of translational research. Recently, we established a genetically engineered ornithine transcarbamylase-deficient (OTCD) pig strain. Here, we report its characterization and treatment responsiveness. OTCD pigs were obtained by mating an OTCD carrier female (OTC-X^c.186_190delX^WT) with a wild-type male. Due to the X-linked recessive mode of inheritance, the disease phenotype emerged only in males. Medication with nitrogen-scavenging agents was based on a clinical protocol. OTCD pigs were born smaller than their wild-type and carrier littermates, showing anemia and faltering. Biochemically, high levels of urinary orotic acid and loss of OTC activity were observed. The natural life course of OTCD pigs was characterized by a decrease in arterial percentage saturation of oxygen and body temperature, as well as an increase in blood ammonia levels; the pigs died in 24.0 ± 5.0 h (mean ± SD, n = 6). The established standard medication composed with nitrogen-scavenging agents and transfusion nearly doubled the survival time to 42.4 ± 13.7 h (n = 6). Our OTCD pig model appropriately mimicked the human pathology. Along with established protocols in handling and medication, this is a first step in developing a large animal disease model that is useful for translational research into novel medical technologies, such as cell transplantation and gene therapy, as well as in relation to urea cycle disorder.

Liver transplantation in children with inborn errors of metabolism: 30 years experience in NSW, Australia

BACKGROUND

Inborn errors of metabolism (IEM) are a diverse group of genetic disorders that can result in significant morbidity and sometimes death. Metabolic management can be challenging and burdensome for families. Liver transplantation (LT) is increasingly being considered a treatment option for some IEMs. IEMs are now considered the second most common reason for pediatric LT.

AIM

To review the data of all children with an IEM who had LT at The Children's Hospital at Westmead (CHW), NSW, Australia between January 1986 and January 2019.

METHODS

Retrospective data collected from the medical records and genetic files included patient demographics, family history, parental consanguinity, method of diagnosis of IEM, hospital and intensive care unit admissions, age at LT, graft type, clinical outcomes and metabolic management pre and post-LT.

RESULTS

Twenty-four LT were performed for 21 patients. IEM diagnoses were MSUD (n = 4), UCD (n = 8), OA (n = 6), TYR type I (n = 2) and GSD Ia (n = 1). Three patients had repeat transplants due to complications. Median age at transplant was 6.21 years (MSUD), 0.87 years (UCD), 1.64 years (OA) and 2.2 years (TYR I). Two patients died peri-operatively early in the series, one died 3 months after successful LT due to septicemia. Eighteen LTs have been performed since 2008 in comparison to six LT prior to 2008. Dietary management was liberalized post LT for all patients.

CONCLUSIONS

Referral for LT for IEMs has increased over the last 33 years, with the most referrals in the last 10 years. Early LT has resulted in improved clinical outcomes and patient survival.

Identification of rare variants causing urea cycle disorders: A clinical, genetic, and biophysical study

Urea cycle disorders (UCDs) are a group of rare metabolic conditions characterized by hyperammonemia and a broad spectrum of phenotypic severity. They are caused by the congenital deficiency in the eight biomolecules involved in urea cycle. In the present study, five cases of UCD were recruited and submitted to a series of clinical, biochemical, and genetic analysis with a combination of high throughput techniques. Moreover, in silico analysis was conducted on the identified missense genetic variants. Various clinical and biochemical indications (including profiles of amino acids and urinary orotic acids) of UCD were manifested by the five probands. Sequence analysis revealed nine diagnostic variants, including three novel ones, which caused Argininosuccinic aciduria (ASA) in one case, Carbamoyl phosphate synthetase 1deficiency (CPS1D) in two cases, Ornithine transcarbamylase deficiency (OTCD) in one case, and Citrin deficiency in 1case. Results of in silico biophysical analysis strongly suggested the pathogenicity of each the five missense variants and provided insight into their intramolecular impacts. In conclusion, this study expanded the genetic variation spectrum of UCD, gave solid evidence for counselling to the affected families, and should facilitate the functional study on the proteins in urea cycle.

Correction of a urea cycle defect after ex vivo gene editing of human hepatocytes

Ornithine transcarbamylase deficiency (OTCD) is a monogenic disease of ammonia metabolism in hepatocytes. Severe disease is frequently treated by orthotopic liver transplantation. An attractive approach is the correction of a patient’s own cells to regenerate the liver with gene-repaired hepatocytes. This study investigates the efficacy and safety of ex vivo correction of primary human hepatocytes. Hepatocytes isolated from an OTCD patient were genetically corrected ex vivo, through the deletion of a mutant intronic splicing site achieving editing efficiencies >60% and the restoration of the urea cycle in vitro. The corrected hepatocytes were transplanted into the liver of FRGN mice and repopulated to high levels (>80%). Animals transplanted and liver repopulated with genetically edited patient hepatocytes displayed normal ammonia, enhanced clearance of an ammonia challenge and OTC enzyme activity, as well as lower urinary orotic acid when compared to mice repopulated with unedited patient hepatocytes. Gene expression was shown to be similar between mice transplanted with unedited or edited patient hepatocytes. Finally, a genome-wide screening by performing CIRCLE-seq and deep sequencing of >70 potential off-targets revealed no unspecific editing. Overall analysis of disease phenotype, gene expression, and possible off-target editing indicated that the gene editing of a severe genetic liver disease was safe and effective.

The Application of Neurodiagnostic Studies to Inform the Acute Management of a Newborn Presenting With Sarbamoyl Shosphate Synthetase 1 Deficiency

Neonatal-onset urea cycle disorders (UCDs) may result in hyperammonemic (HA) encephalopathy presenting with several neurologic sequelae including seizures, coma, and death. However, no recommendations are given in how and when neurodiagnostic studies should be used to screen or assess for these neurologic complications. We present a case of carbamoyl phosphate synthetase 1 (CPS1) deficiency in a newborn female in which electroencephalogram monitoring to assess encephalopathy and seizures, and magnetic resonance imaging measurements of brain metabolites were used to guide care during her hyperammonemic crisis. Her neurologic course and response to treatment characterizes the significant neurologic impact of HA encephalopathy. Our group herein proposes a clinical neurodiagnostic pathway for managing acute HA encephalopathy.

Irritability, Poor Feeding and Respiratory Alkalosis in Newborns: Think about Metabolic Emergencies. A Brief Summary of Hyperammonemia Management

The urea cycle is a series of metabolic reactions that convert ammonia into urea in order to eliminate it from the body. Urea cycle disorders are characterized by hyperammonemia, which can cause irreversible damages in central nervous system. We report a series of three newborns presenting irritability, poor feeding and tachypnea. Their first gas analysis revealed respiratory alkalosis. Hyperammonemia was confirmed, and three different enzymatic blocks in the urea cycle were diagnosed. Immediate treatment consisted in the removal of ammonia by reduction of the catabolic state, dietary adjustments, use of nitrogen scavenging agents and ultimately hemodiafiltration. Hyperammonemia is a medical emergency whose treatment should not be delayed. This report aims to highlight the importance of suspecting urea cycle disorders in newborns with aspecific signs of hyperammonemia and respiratory alkalosis, and to sum up the broad lines of hyperammonemia management.

Urea Cycle Disorders: A Neuroimaging Pattern Approach Using Diffusion and FLAIR MRI

BACKGROUND AND PURPOSE

This study aimed to assess characteristic regions of MRI involvement utilizing diffusion weighted imaging (DWI) and fluid-attenuated inversion recovery (FLAIR) at urea cycle disorder (UCD) diagnosis to determine the possible association between initial MRI patterns within 10 days of the first hyperammonemia episode, serum ammonia levels, and severity of neurological outcome based on clinical follow-up of >30 days.

METHODS

Ten patients with UCDs (4 females; median age: 5.4 years, age range: 6 days-54 years) were included who underwent MRI during a first episode of hyperammonemia. The topographical distribution of the DWI and FLAIR abnormalities in the cerebral cortex, deep gray matter, white matter, posterior limb of internal capsule, cerebral peduncle, and cerebellum was evaluated. Possible correlations between the brain injury patterns on DWI/FLAIR images, serum ammonia levels, and severity of neurological outcome were investigated by a trend correlation.

RESULTS

The UCD cohort (n = 10) involved four ornithine transcarbamoylase deficiencies, four argininosuccinic aciduria, one carbomoylphosphate synthetase deficiency, and one citrullinemia type-1. The observed trend in the distribution of DWI abnormalities as the severity of neurological sequela outcome increased was with diffuse cerebral cortex or corpus striatum involvement. Patients with initial peak serum ammonia ≥450 µmol/L had a grade 2 to 4 outcome, and those with peak ammonia <450 µmol/L had a grade 0 or 1 outcome.

CONCLUSIONS

The presence of more severe neurological outcome could be associated with diffuse cerebral cortex or corpus striatum involvement on DWI and high serum ammonia levels in patients with UCD.

Clinical and genetic analysis of five Chinese patients with urea cycle disorders

BACKGROUND

The urea cycle plays a key role in preventing the accumulation of toxic nitrogenous waste products, including two essential enzymes: ornithine transcarbamylase (OTC) and argininosuccinate lyase (ASL). Ornithine transcarbamylase deficiency (OTCD) results from mutations in the OTC. Meanwhile, argininosuccinate lyase deficiency (ASLD) is caused by mutations in the ASL.

METHODS

Blood tandem mass spectrometric analysis and urea organic acidemia screening were performed on five Chinese cases, including three OTCD and two ASLD patients. Next-generation sequencing was then used to make a definite diagnosis, and the related variants were validated by Sanger sequencing.

RESULTS

The five patients exhibited severe clinical symptoms, with abnormal biochemical analysis and amino acids profile. Genetic analysis revealed two variants [c.77G>A (p.Arg26Gln); c.116G>T (p.Gly39Val)] in the OTC, as well as two variants [c.1311T>G (p.Tyr437*); c.961T>A (p.Tyr321Asn)] in the ASL. Conservation analysis showed that the amino acids of the two novel mutations were highly conserved in different species and were predicted to be possibly damaging with several in silico prediction programs. 3D-modeling analysis indicated that the two novel missense variants might result in modest distortions of the OTC and ASL protein structures, respectively.

CONCLUSIONS

Two novel variants expand the mutational spectrums of the OTC and ASL. All the results may contribute to a better understanding of the clinical course and genetic characteristics of patients with urea cycle disorders.

Split AAV-Mediated Gene Therapy Restores Ureagenesis in a Murine Model of Carbamoyl Phosphate Synthetase 1 Deficiency

The urea cycle enzyme carbamoyl phosphate synthetase 1 (CPS1) catalyzes the initial step of the urea cycle; bi-allelic mutations typically present with hyperammonemia, vomiting, ataxia, lethargy progressing into coma, and death due to brain edema if ineffectively treated. The enzyme deficiency is particularly difficult to treat; early recognition is essential to minimize injury to the brain. Even under optimal conditions, therapeutic interventions are of limited scope and efficacy, with most patients developing long-term neurologic sequelae. One significant encumberment to gene therapeutic development is the size of the CPS1 cDNA, which, at 4.5 kb, nears the packaging capacity of adeno-associated virus (AAV). Herein we developed a split AAV (sAAV)-based approach, packaging the large transgene and its regulatory cassette into two separate vectors, thereby delivering therapeutic CPS1 by a dual vector system with testing in a murine model of the disorder. Cps1-deficient mice treated with sAAVs survive long-term with markedly improved ammonia levels, diminished dysregulation of circulating amino acids, and increased hepatic CPS1 expression and activity. In response to acute ammonia challenging, sAAV-treated female mice rapidly incorporated nitrogen into urea. This study demonstrates the first proof-of-principle that sAAV-mediated therapy is a viable, potentially clinically translatable approach to CPS1 deficiency, a devastating urea cycle disorder.

ECMO as a Platform for Rapid Ammonia Removal in a Neonate with Multienzyme Urea Cycle Disorder

Since the initial deployment of neonatal extracorporeal membrane oxygenation (ECMO) for respiratory failure, the use of ECMO in this population has diversified. We present a term female infant with carbamoyl phosphate synthetase 1 and partial N-acetylglutamate synthase deficiencies who developed severe hyperammonemia refractory to medical management requiring venoarterial ECMO-driven continuous veno-venous hemodiafiltration for ammonia detoxification. This case report illustrates a subpopulation where neonatal ECMO may improve survival and neurodevelopmental outcomes. To our knowledge, this is the first reported case of a urea cycle defect arising from two proximal enzyme deficiencies. Also, this is one of the few reported patients with UCD associated with peak ammonia levels >2,000 μmol/L who survived to hospital discharge after the successful use of ECMO for ammonia reduction. This case will add to the existing scant literature supporting the use of ECMO as a platform for rapid removal of serum ammonia.

Pre-school neurocognitive and functional outcomes after liver transplant in children with early onset urea cycle disorders, maple syrup urine disease, and propionic acidemia: An inception cohort matched-comparison study

Background

Urea cycle disorders (UCD) and organic acid disorders classically present in the neonatal period. In those who survive, developmental delay is common with continued risk of regression. Liver transplantation improves the biochemical abnormality and patient survival is good. We report the neurocognitive and functional outcomes post‐transplant for nine UCD, three maple syrup urine disease, and one propionic acidemia patient.

Methods

Thirteen inborn errors of metabolism (IEM) patients were individually one‐to‐two matched to 26 non‐IEM patients. All patients received liver transplant. Wilcoxon rank sum test was used to compare full‐scale intelligence‐quotient (FSIQ) and Adaptive Behavior Assessment System‐II General Adaptive Composite (GAC) at age 4.5 years. Dichotomous outcomes were reported as percentages.

Results

FSIQ and GAC median [IQR] was 75 [54, 82.5] and 62.0 [47.5, 83] in IEM compared with 94.5 [79.8, 103.5] and 88.0 [74.3, 97.5] in matched patients (P‐value <.001), respectively. Of IEM patients, 6 (46%) had intellectual disability (FSIQ and GAC <70), 5 (39%) had autism spectrum disorder, and 1/13 (8%) had cerebral palsy, compared to 1/26 (4%), 0, 0, and 0% of matched patients, respectively. In the subgroup of nine with UCDs, FSIQ (64[54, 79]), and GAC (56[45, 75]) were lower than matched patients (100.5 [98.5, 101] and 95 [86.5, 99.5]), P = .005 and .003, respectively.

Conclusion

This study evaluated FSIQ and GAC at age 4.5 years through a case‐comparison between IEM and matched non‐IEM patients post‐liver transplantation. The neurocognitive and functional outcomes remained poor in IEM patients, particularly in UCD. This information should be included when counselling parents regarding post‐transplant outcome.

Challenges in diagnosing and managing adult patients with urea cycle disorders

Urea cycle disorders (UCD) are a group of rare inherited metabolic conditions of amino acid catabolism caused by an enzyme deficiency within the hepatic ammonia detoxification pathway. The presentation of these disorders ranges from life-threatening intoxication in the neonate to asymptomatic status in adults. Late-onset UCDs can present for the first time in adulthood and may mimic other causes of acute confusion or psychiatric diseases, and are often associated with neurological symptoms. Late-onset UCDs may become apparent during periods of metabolic stress such as rapid weight loss, gastric bypass surgery, chronic starvation or the postpartum period. Early diagnosis is critical for effective treatment and to prevent long-term complications of hyperammonemia. The challenges of management of adults include for example: (a) poor compliance to dietary and medical treatment which can result in recurrent hospital admissions; (b) severe neurological dysfunction; (c) the management of pregnancy and the postpartum period; and (d) access to multidisciplinary care peri-operatively. In this review, we highlight a number of challenges in the diagnosis and management of adult patient with late-onset UCDs and suggest a systematic management approach.

[Clinical features of children with lysinuric protein intolerance and SLC7A7 gene mutation: an analysis of 3 cases]

Lysinuric protein intolerance (LPI) is an autosomal recessive disorder caused by SLC7A7 gene mutation and often involves severe lesions in multiple systems. Lung involvement is frequently seen in children with LPI and such children tend to have a poor prognosis. This article summarizes the clinical manifestations and gene mutation characteristics of three children diagnosed with LPI by SLC7A7 gene analysis. All three children had the manifestations of aversion to protein-rich food after weaning, delayed development, anemia, hepatosplenomegaly, and osteoporosis, as well as an increase in orotic acid in urine. In addition, interstitial pneumonia and diffuse pulmonary interstitial lesions were observed in two children. SLC7A7 gene detection showed three pathogenic mutations in these children, namely c.1387delG(p.V463CfsX56), c.1215G>A(p.W405X) and homozygous c.625+1G>A. After a definite diagnosis was made, all three children were given a low-protein diet and oral administration of citrulline [100 mg/(kg.d)], iron protein succinylate [4 mg/(kg.d)], calcium and zinc gluconates oral solution (10 mL/day) and vitamin D (400 IU/day). In addition, patient 3 was given prednisone acetate (5 mg/day). The children had varying degrees of improvement in symptoms and signs. It is hard to distinguish LPI from urea cycle disorder due to the features of amino acid and organic acid metabolism in LPI, and SLC7A7 gene analysis is the basis for a definite diagnosis of LPI.

Hyperammonemia in a Woman with Late-onset Ornithine Transcarbamylase Deficiency

A 52-year-old woman developed vomiting and disturbance of consciousness after consuming raw fish and sushi on a trip. A blood test showed hyperammonemia (310 μg/dL) with a normal liver function. She fell into a deep coma, and her serum ammonia level increased to 684 μg/dL. L-arginine was administered as a diagnostic treatment for urea cycle disorder (UCD) and serum ammonia, and her consciousness levels improved. She was diagnosed with ornithine transcarbamylase deficiency (OTCD) by analyses of plasma amino acids, urinary orotic acid, and the OTC gene mutation. UCD should be considered for patients with hyperammonemia without severe liver function abnormalities.

Hyperornithinemia-hyperammonemia-homocitrullinuria syndrome in pregnancy: Considerations for management and review of the literature

Hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome is a rare metabolic autosomal recessive urea cycle disorder. Only about 100 patients have been reported in the literature. As the population survives into reproductive years, pregnancy management becomes a new challenge for this clinicians. To our knowledge, there are less than three patients with successful pregnancies and deliveries found in the literature with no specific consensus on management or recommendations for HHH syndrome. We reviewed the current literature regarding pregnancy outcomes, combine it with our experience managing a patient through two successful pregnancies and identify a new concern of fetal intrauterine growth restriction. From this, recommendations for pregnancy management are made, including a detailed protocol for clinicians to use for disease management at delivery and in the post-partum period.

Untargeted metabolomic profiling reveals multiple pathway perturbations and new clinical biomarkers in urea cycle disorders

Purpose:

Untargeted metabolomic analysis is increasingly being used in the screening and management of individuals with inborn errors of metabolism (IEM). We aimed to test whether untargeted metabolomic analysis in plasma might be useful for monitoring the disease course and management of urea cycle disorders (UCDs).

Methods:

Untargeted mass spectrometry-based metabolomic analysis was used to generate z-scores for more than 900 metabolites in plasma from 48 individuals with various UCDs. Pathway analysis was used to identify common pathways that were perturbed in each UCD.

Results:

Our metabolomic analysis in plasma identified multiple potentially neurotoxic metabolites of arginine in arginase deficiency and, thus, may have utility in monitoring the efficacy of treatment in arginase deficiency. In addition, we were also able to detect multiple biochemical perturbations in all UCDs that likely reflect clinical management, including metabolite alterations secondary to dietary and medication management.

Conclusions:

In addition to utility in screening for IEM, our results suggest that untargeted metabolomic analysis in plasma may be beneficial for monitoring efficacy of clinical management and off-target effects of medications in UCDs and potentially other IEM.

Acute Presentation and Management of the Encephalopathic Child With an Undiagnosed Inborn Error of Metabolism

BACKGROUND

Inborn errors of metabolism (IEM) commonly present in infancy and, less commonly, later in life.

CASE REPORT

This case describes an IEM, specifically, ornithine transcarbamylase deficiency, in a previously healthy 7-year-old boy who presented to an emergency department with vomiting for approximately 24 h prior to admission. The child became progressively encephalopathic while in the emergency department, but an ammonia level was not obtained until several hours after admission. Irreversible brain damage with cerebral edema was already present at time of diagnosis, leading to death. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: This case emphasizes that acute hyperammonemia can rapidly cause irreversible neurological damage and, in the case of a newly encephalopathic pediatric patient, ammonia levels should be evaluated early to facilitate proper diagnostic tests and treatment.

Early liver transplantation in neonatal-onset and moderate urea cycle disorders may lead to normal neurodevelopment

Urea cycle disorders (UCDs) are inherited metabolic diseases that lead to hyperammonemia. Neurodevelopmental outcomes of patients with UCDs depend on the maximum ammonia concentration (MAC) in the blood during onset. MAC ≥360 μM is a marker of poor neurodevelopmental outcomes. We investigated the neurodevelopmental outcomes and MAC at onset for 177 patients with UCDs in Japan (median age, 8 years and 2 months; range, 10 days-72 years), including 57 patients with male ornithine transcarbamylase (OTCD), 59 patients with female OTCD, 23 patients with carbamoyl-phosphate synthetase 1 deficiency (CPSD), 28 patients with arginosuccinate synthetase deficiency, 9 patients with arginosuccinate lyase deficiency (ALD), and 1 patient with arginase 1 deficiency. Neurodevelopmental outcomes of patients with CPSD and ALD were poor because most had neonatal onset with blood MAC ≥300 μM at onset. Although OTCD, particularly female late-onset OTCD, has good neurodevelopmental outcomes among those with UCDs, it is not necessarily a mild disease with good long-term outcomes. Patients with severe UCDs and MAC ≥300 μM at onset should undergo liver transplantation (LT). Moreover, this study suggested that if the onset of UCD began during the neonatal period, then even UCD patients with MAC <300 μM at onset should undergo LT to protect the brain.

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.

Split-graft liver transplantation from an adult donor with an unrecognized UCD to a pediatric and adult recipient

We report the outcomes of an adult and pediatric split liver transplant from an adult male donor who died due to an unrecognized UCD, OTC deficiency. Recognizing inborn errors of metabolism can be challenging, especially in adult centers where such disorders are rarely encountered. Shortage of donors for liver transplantation has led to procedures to maximize donor utilization, such as split and live donor grafts. The cause of death should be ascertained before accepting a cadaveric donor organ.

The Relationship between Dietary Intake, Growth, and Body Composition in Inborn Errors of Intermediary Protein Metabolism

OBJECTIVES

To examine relationships between dietary intake, growth and body composition patterns in patients with inborn errors of intermediary protein metabolism and to determine a safe protein:energy ratio (P:E ratio) associated with optimal growth outcomes.

STUDY DESIGN

Retrospective longitudinal data of growth and dietary intake in patients (n = 75) with isovaleric acidemia (IVA; n = 7), methylmalonic acidemia/propionic acidemia (MMA/PA; n = 14), urea cycle defects (UCD; n = 44), classical maple syrup urine disease (MSUD; n = 10) were collected. Prospective longitudinal data of growth, dietary intake, and body composition from 21 patients: IVA (n = 5), MMA/PA (n = 6), UCD (n = 7), and MSUD (n = 3) were collected at clinic visits.

RESULTS

Fifty-two of 75 (66%), 49 of 74 (68%), and 44 of 65 (68%) patients had a z-score of 0 (±1) for lifetime weight, height, and body mass index, respectively. Patients with MMA/PA had the lowest median height and weight z-scores, and MSUD patients had highest median body mass index z-score at all ages. In IVA, MMA/PA, and UCD, total natural protein intake met or exceeded the Food and Agriculture Organization of the United Nations (FAO)/World Health Organization (WHO)/United Nations University (UNU) recommended safe levels. Median percentage fat mass was 17.6% in IVA, 20.7% in MMA/PA, 19.4% in UCD, and 17.8% in MSUD. There was a significant negative correlation between percentage fat mass and total protein intake in IVA, MMA/PA, and UCD (r = -0.737; P = .010). The correlation between the P:E ratio and growth variables in IVA, MMA/PA, and UCD suggest a safe P:E ratio (>1.5 to < 2.9) g protein:100 kcal/day.

CONCLUSION

Growth outcomes in inborn errors of intermediary protein metabolism are not always ideal. Most patients with IVA, MMA/PA, and UCD consume sufficient natural protein to meet FAO/WHO/UNU recommendations. A P:E ratio range of (>1.5 to < 2.9)g protein/100 kcal/day correlates with optimal growth outcomes.

Citrulline for urea cycle disorders in Japan

BACKGROUND

The amino acid l-citrulline is used as a therapeutic agent for urea cycle disorders (UCD) including ornithine transcarbamylase deficiency (OTCD), carbamoyl phosphate synthetase I deficiency (CPSD), and N-acetylglutamate synthase deficiency. There are few reports, however, on the use of l-citrulline in Japan and little consensus regarding the effects of l-citrulline.

METHODS

We conducted a questionnaire survey of patients undergoing l-citrulline treatment for a UCD to evaluate the current status of this therapy. The survey included patient background, details of l-citrulline treatment, clinical examination data, treatment, frequency of vomiting, and liver transplantation.

RESULTS

We retrospectively investigated 43 questionnaire respondents (OTCD, n = 33; CPSD, n = 10). The weight of male OTCD patients improved by +0.79 SD, and the ammonia level decreased by a mean of 44.3 μmol/L in all patients. The protein intake of all patients and of male OTCD patients increased by 0.14 g/kg/day and 0.17 g/kg/day, respectively.

CONCLUSIONS

l-Citrulline effectively reduced ammonia level, increased protein intake, and improved weight gain in UCD patients. l-Citrulline should be considered a standard therapy in OTCD and CPSD patients.

Late onset arginase deficiency presenting with encephalopathy and midbrain hyperintensity

Urea cycle disorders (UCD) are very rare metabolic disorders that present with encephalopathy and hyperammonemia. Of the UCDs, Arginase deficiency (ARD) is the rarest and presents in childhood with a progressive spastic diplegia or seizures. Acute presentation in adulthood is extremely unusual.[1] We present the first case of adult onset ARD presenting with encephalopathy and diffusion weighted MRI findings that resembled a moustache in the midbrain.

Carglumic acid promotes apoptosis and suppresses cancer cell proliferation in vitro and in vivo

Drug repurposing is a therapeutic strategy that applies drugs to treat different diseases based on new therapeutic function. Carglumic acid (Carbaglu; Orphan Europe) is an orphan drug approved by the FDA for hyperammonemia. Administration of carglumic acid for treatment of hyperammonemia has few side effects and has been used for 10 years to effectively treat hyperammonemia symptoms of both adult and pediatric patients. Here, we tested the potential of carglumic acid to be repurposed as an anticancer agent and showed that carglumic acid promotes apoptosis and inhibits cancer cell growth ina wide variety of human cancers, including pancreatic ductal adenocarcinoma, triple-negative breast cancer (TNBC), hepatoma, and lung cancer. Our data from in vivo models indicates that orally taking 10% of the carglumic acid dose currently used for the treatment of hyperammonemia ise ffective to suppress the growth of pancreatic ductal adenocarcinomaand TNBC. If given intravenously, only 5% of the carglumic acid doseis needed to be effective against TNBC. These findings suggest that carglumic acid may serve as a safe and effective therapeutic to treat both TNBC and pancreatic cancer.

Neonatal citrullinemia: novel, reversible neuroimaging findings correlated with ammonia level changes

BACKGROUND

Citrullinemia type I is an autosomal recessive disorder of the urea cycle in which a patient lacks the cytosolic enzyme, argininosuccinic acid synthetase. This enzyme deficiency results in elevated levels of ammonia, glutamine, and citrulline. The accumulation of ammonia and glutamine causes neurodegenerative changes that are detectible on magnetic resonance imaging. This is the first case report of citrullinemia with repeat magnetic resonance images and electroencephalographs in the acute phase of hyperammonemia.

CASE

This 3800 g white boy was born at 40 weeks 4 days gestation to a 25-year-old mother. He was delivered at home to a certified midwife with no reported complications. He was doing well until day of life 4, when the mother reported he would no longer latch to feed. He was observed to have markedly elevated ammonia levels and ultimately diagnosed with citrullinemia type I. The initial magnetic resonance image was markedly abnormal. After aggressive medical management, his repeat magnetic resonance image revealed marked improvement in the acute setting.

CONCLUSION

Early and aggressive management of hyperammonemia can result in improved magnetic resonance imaging findings in the acute setting. It is too early to know if this will translate to an improved clinical outcome. Clinical suspicion must remain high for urea cycle disorders in neonates with magnetic resonance image changes similar to those resulting from hypoxic-ischemic injury.

Elevated phenylacetic acid levels do not correlate with adverse events in patients with urea cycle disorders or hepatic encephalopathy and can be predicted based on the plasma PAA to PAGN ratio

BACKGROUND

Phenylacetic acid (PAA) is the active moiety in sodium phenylbutyrate (NaPBA) and glycerol phenylbutyrate (GPB, HPN-100). Both are approved for treatment of urea cycle disorders (UCDs) - rare genetic disorders characterized by hyperammonemia. PAA is conjugated with glutamine in the liver to form phenylacetyleglutamine (PAGN), which is excreted in urine. PAA plasma levels ≥ 500 μg/dL have been reported to be associated with reversible neurological adverse events (AEs) in cancer patients receiving PAA intravenously. Therefore, we have investigated the relationship between PAA levels and neurological AEs in patients treated with these PAA pro-drugs as well as approaches to identifying patients most likely to experience high PAA levels.

METHODS

The relationship between nervous system AEs, PAA levels and the ratio of plasma PAA to PAGN were examined in 4683 blood samples taken serially from: [1] healthy adults [2], UCD patients of ≥ 2 months of age, and [3] patients with cirrhosis and hepatic encephalopathy (HE). The plasma ratio of PAA to PAGN was analyzed with respect to its utility in identifying patients at risk of high PAA values.

RESULTS

Only 0.2% (11) of 4683 samples exceeded 500 μg/ml. There was no relationship between neurological AEs and PAA levels in UCD or HE patients, but transient AEs including headache and nausea that correlated with PAA levels were observed in healthy adults. Irrespective of population, a curvilinear relationship was observed between PAA levels and the plasma PAA:PAGN ratio, and a ratio>2.5 (both in μg/mL) in a random blood draw identified patients at risk for PAA levels>500 μg/ml.

CONCLUSIONS

The presence of a relationship between PAA levels and reversible AEs in healthy adults but not in UCD or HE patients may reflect intrinsic differences among the populations and/or metabolic adaptation with continued dosing. The plasma PAA:PAGN ratio is a functional measure of the rate of PAA metabolism and represents a useful dosing biomarker.

Improving surveillance for hyperammonemia in the newborn

OBJECTIVE

Prompt ascertainment is crucial for the management of hyperammonemic infants. Because these patients are rare and recognition of hyperammonemia is often delayed, we designed and implemented an electronic medical record (EMR)-based tool to assist physicians in the detection of hyperammonemia.

METHODS

We retrospectively evaluated the hospitalizations of prior hyperammonemic infants to identify codable elements that could trigger an EMR-based warning. An alert was designed and implemented and its utilization was prospectively analyzed.

RESULTS

Blood gas studies were obtained universally and early in the retrospectively evaluated infants (x¯=26h before ammonia level). Prompting physicians to evaluate ammonia after ordering blood gas studies would have accelerated the initial ammonia order in 89% of retrospective cases. The alert has activated 184 times over the first six months of operation leading to 63 laboratory evaluations and detection of one hyperammonemic infant.

CONCLUSION

Implementation of an EMR-based warning system can improve surveillance for hyperammonemia in a susceptible population.

Feasibility of adjunct therapeutic hypothermia treatment for hyperammonemia and encephalopathy due to urea cycle disorders and organic acidemias

BACKGROUND

Children with urea cycle disorders (UCDs) or organic acidemias (OAs) and acute hyperammonemia and encephalopathy are at great risk for neurological injury, developmental delay, intellectual disability, and death. Nutritional support, intravenous alternative pathway therapy, and dialysis are used to treat severe hyperammonemia associated with UCDs and nutritional support and dialysis are used to treat severe hyperammonemia in OAs. Brain protective treatment while therapy is initiated may improve neurological and cognitive function for the lifetime of the child. Animal experiments and small clinical trials in hepatic encephalopathy caused by acute liver failure suggest that therapeutic hypothermia provides neuroprotection in hyperammonemia associated encephalopathy. We report results of an ongoing pilot study that assesses if whole body cooling during rescue treatment of neonates with acute hyperammonemia and encephalopathy is feasible and can be conducted safely.

METHODS

Adjunct whole body therapeutic hypothermia was conducted in addition to standard treatment in acutely encephalopathic, hyperammonemic neonates with UCDs and OAs requiring dialysis. Therapeutic hypothermia was initiated using cooling blankets as preparations for dialysis were underway. Similar to standard therapeutic hypothermia treatment for neonatal hypoxic ischemic encephalopathy, patients were maintained at 33.5°C±1°C for 72h, they were then slowly rewarmed by 0.5°C every 3h over 18h. In addition data of age-matched historic controls were collected for comparison.

RESULTS

Seven patients were cooled using the pilot study protocol and data of seven historic controls were reviewed. All seven patients survived the initial rescue and cooling treatment, 6 patients were discharged home 2-4weeks after hospitalization, five of them feeding orally. The main complication observed in a majority of patients was hypotension.

CONCLUSION

Adjunct therapeutic hypothermia for neonates with UCDs and OAs receiving standard treatment was feasible and could be conducted safely in pediatric and neonatal intensive care units experienced in the application of therapeutic hypothermia in critically ill neonates. However, including adjunct therapeutic hypothermia in the already involved treatment regimen of critically ill patients with hyperammonemia and encephalopathy adds to the complexity of care and should not be done unless it is proven efficacious in a randomized clinical trial.

N-acetylglutamate synthase deficiency: an insight into the genetics, epidemiology, pathophysiology, and treatment

The conversion of ammonia into urea by the human liver requires the coordinated function of the 6 enzymes and 2 transporters of the urea cycle. The initial and rate-limiting enzyme of the urea cycle, carbamylphosphate synthetase 1 (CPS1), requires an allosteric activator, N-acetylglutamate (NAG). The formation of this unique cofactor from glutamate and acetyl Coenzyme-A is catalyzed by N-acetylglutamate synthase (NAGS). An absence of NAG as a consequence of NAGS deficiency may compromise flux through CPS1 and result in hyperammonemia. The NAGS gene encodes a 528-amino acid protein, consisting of a C-terminal catalytic domain, a variable segment, and an N-terminal mitochondrial targeting signal. Only 22 mutations in the NAGS gene have been reported to date, mostly in the catalytic domain. NAGS is primarily expressed in the liver and intestine. However, it is also surprisingly expressed in testis, stomach and spleen, and during early embryonic development at levels not concordant with the expression of other urea cycle enzymes, CPS1, or ornithine transcarbamylase. The purpose of NAGS expression in these tissues, and its significance to NAGS deficiency is as yet unknown. Inherited NAGS deficiency is the rarest of the urea cycle disorders, and we review the currently reported 34 cases. Treatment of NAGS deficiency with N-carbamyglutamate, a stable analog of NAG, can restore deficient urea cycle function and normalize blood ammonia in affected patients.

New developments in the treatment of hyperammonemia: emerging use of carglumic acid

Hyperammonemia is a true neonatal emergency with high toxicity for the central nervous system and developmental delay. The causes of neonatal hyperammonemia are genetic defects of urea cycle enzymes, organic acidemias, lysinuric protein intolerance, hyperammonemia-hyperornithinemia- homocitrullinemia syndrome, transient hyperammonemia of the newborn, and congenital hyperinsulinism with hyperammonemia. In some of these conditions the high blood ammonia levels are due to the reduction of N-acetylglutamate, an essential cofactor necessary for the function of the urea cycle, or to the reduction of carbamoyl-phosphate synthase-I activity. In these cases, N-carbamylglutamate (carglumic acid) can be administered together with the conventional therapy. Carglumic acid is an analog of N-acetylglutamate that has a direct action on carbamoyl-phosphate synthase-I. Its effects are reactivation of the urea cycle and reduction of plasma ammonia levels. As a consequence it improves the traditional treatment, avoiding the need of hemodialysis and peritoneal dialysis. In this review we evaluate the possible field of application of carglumic acid and its effectiveness and safety.

Establishing a consortium for the study of rare diseases: The Urea Cycle Disorders Consortium

The Urea Cycle Disorders Consortium (UCDC) was created as part of a larger network established by the National Institutes of Health to study rare diseases. This paper reviews the UCDC's accomplishments over the first 6years, including how the Consortium was developed and organized, clinical research studies initiated, and the importance of creating partnerships with patient advocacy groups, philanthropic foundations and biotech and pharmaceutical companies.

Argininosuccinate lyase deficiency: longterm outcome of 13 patients detected by newborn screening

Argininosuccinate lyase deficiency is a urea cycle disorder which can present in the neonatal period with hyperammonemic encephalopathy, or later in childhood with episodic vomiting, growth and developmental delay. Abnormal hair, hepatomegaly, and hepatic fibrosis are unique features of this disorder. Twelve patients with argininosuccinate lyase deficiency were ascertained between 4 and 6 weeks of age by urine amino acid screening. One infant in a previously identified family was diagnosed shortly after birth. Diagnosis was confirmed by enzyme assay in red blood cells and/or skin fibroblasts. At the time of last follow-up, patients had been followed for 13-33 years. All patients were asymptomatic at detection, 7 had slightly increased blood ammonia, and all were initially treated with low-protein diet. Utilization of (14)C-citrulline by intact skin fibroblasts measured by (14)C incorporation into macromolecules was 74-135% of the control mean for 7 of the 8 patients studied. Nine patients had normal development, 4 had learning disability, 6 had EEG abnormalities, 3 had seizure disorder. None had any episodes of hyperammonemic coma. None had hepatomegaly. Patients detected by screening had higher enzyme activity measured by the (14)C-citrulline incorporation assay than comparison groups of patients with neonatal-onset and with late-onset detected by clinical disease. The ability to utilize (14)C-citrulline by intact fibroblasts seems to correlate with clinical outcome and may have prognostic value. It is likely that early diagnosis and treatment contributed to the relatively mild clinical course of the study group.