Urea Cycle Disorders: Clinical Presentation Outside the Newborn Period

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.

Extending inherited metabolic disorder diagnostics with biomarker interaction visualizations

BACKGROUND

Inherited Metabolic Disorders (IMDs) are rare diseases where one impaired protein leads to a cascade of changes in the adjacent chemical conversions. IMDs often present with non-specific symptoms, a lack of a clear genotype-phenotype correlation, and de novo mutations, complicating diagnosis. Furthermore, products of one metabolic conversion can be the substrate of another pathway obscuring biomarker identification and causing overlapping biomarkers for different disorders. Visualization of the connections between metabolic biomarkers and the enzymes involved might aid in the diagnostic process. The goal of this study was to provide a proof-of-concept framework for integrating knowledge of metabolic interactions with real-life patient data before scaling up this approach. This framework was tested on two groups of well-studied and related metabolic pathways (the urea cycle and pyrimidine de-novo synthesis). The lessons learned from our approach will help to scale up the framework and support the diagnosis of other less-understood IMDs.

METHODS

Our framework integrates literature and expert knowledge into machine-readable pathway models, including relevant urine biomarkers and their interactions. The clinical data of 16 previously diagnosed patients with various pyrimidine and urea cycle disorders were visualized on the top 3 relevant pathways. Two expert laboratory scientists evaluated the resulting visualizations to derive a diagnosis.

RESULTS

The proof-of-concept platform resulted in varying numbers of relevant biomarkers (five to 48), pathways, and pathway interactions for each patient. The two experts reached the same conclusions for all samples with our proposed framework as with the current metabolic diagnostic pipeline. For nine patient samples, the diagnosis was made without knowledge about clinical symptoms or sex. For the remaining seven cases, four interpretations pointed in the direction of a subset of disorders, while three cases were found to be undiagnosable with the available data. Diagnosing these patients would require additional testing besides biochemical analysis.

CONCLUSION

The presented framework shows how metabolic interaction knowledge can be integrated with clinical data in one visualization, which can be relevant for future analysis of difficult patient cases and untargeted metabolomics data. Several challenges were identified during the development of this framework, which should be resolved before this approach can be scaled up and implemented to support the diagnosis of other (less understood) IMDs. The framework could be extended with other OMICS data (e.g. genomics, transcriptomics), and phenotypic data, as well as linked to other knowledge captured as Linked Open Data.

S100B Protein but Not 3-Nitrotyrosine Positively Correlates with Plasma Ammonia in Patients with Inherited Hyperammonemias: A New Promising Diagnostic Tool?

Individuals with inherited hyperammonemias often present developmental and intellectual deficiencies which are likely to be exaggerated by hyperammonemia episodes in long-term outcomes. In order to find a new, systemic marker common to the course of congenital hyperammonemias, we decided to measure the plasma level of S100 calcium-binding protein B (S100B), which is associated with cerebral impairment. Further, we analyzed three mechanistically diverged but linked with oxidative-nitrosative stress biochemical parameters: 3-nitrotyrosine (3-NT), a measure of plasma proteins' nitration; advanced oxidation protein products (AOPP), a measure of protein oxidation; and glutathione peroxidase (GPx) activity, a measure of anti-oxidative enzymatic capacity. The plasma biomarkers listed above were determined for the first time in congenital hyperammonemia. Also, the level of pro- and anti-inflammatory mediators (i.e., IL-12, IL-6, IL-8, TNF-α, IL-1β, and IL-10) and chemokines (IP-10, MCP-1, MIG, and RANTES) were quantified. S100B was positively correlated with plasma ammonia level, while noticeable levels of circulating 3-NT in some of the patients' plasma did not correlate with ammonia concentration. Overall, the linear correlation between ammonia and S100B but not standard oxidative stress-related markers offers a unique perspective for the future identification and monitoring of neurological deficits risk-linked with hyperammonemia episodes in patients with inherited hyperammonemias. The S100B measure may support the development of therapeutic targets and clinical monitoring in these disorders.

Risk factors and outcome of hyperammonaemia in people with epilepsy

BACKGROUND

Hyperammonaemia is a recognised complication of antiseizure treatment but risk factors leading to individual patient susceptibility and outcome remain unclear.

OBJECTIVE

To identify risk factors for hyperammonaemia and investigate the impact of its management on clinical outcomes.

METHODS

We carried out a retrospective observational study of adults with epilepsy who had ammonia tested over a 3-year period. Hyperammonaemia was defined as ammonia level > 35 μmol/L. Patients were classified into two groups: hyperammonaemic and non-hyperammonaemic. Association analyses and linear regression analysis were used to identify risk factors for hyperammonaemia.

RESULTS

We reviewed 1002 ammonia requests in total and identified 76 people with epilepsy who had ammonia concentration measured, including 26 with repeated measurements. 59/76 (78%) were found to have hyperammonaemia. There was borderline statistical significance of hyperammonaemia being less common in patients with an established monogenic/metabolic condition than in those with structural or cryptogenic epilepsy (P = 0.05). Drug resistance, exposure to stiripentol and oxcarbazepine were identified as risk factors for hyperammonaemia. We found a dose-dependent association between valproate and hyperammonaemia (P = 0.033). Clinical symptoms were reported in 22/59 (37%) of the hyperammonaemic group. Improved clinical outcomes with concurrent decrease in ammonia concentration were seen in 60% of patients following treatment adjustment.

CONCLUSIONS

Drug resistance and exposure to stiripentol, oxcarbazepine or high-dose valproate are associated with an increased risk of hyperammonaemia. Clinicians should consider symptoms related to hyperammonaemia in patients on high-dose valproate or multiple antiseizure treatments. Prompt identification of hyperammonaemia and subsequent treatment adjustments can lead to improved clinical outcomes.

Liver transplantation in rare late-onset ornithine transcarbamylase deficiency with central nervous system injury: A case report and review of the literature

BACKGROUND

Ornithine transcarbamylase deficiency (OTCD) is a genetic metabolic disease. Its clinical manifestations are mainly central nervous system dysfunction caused by high blood ammonia. Late-onset OTCD combined with central nervous system injury has a poor therapeutic response, which is one of the main factors affecting the prognosis and quality of life of patients. liver transplantation (LT) has gradually become a radical treatment for OTCD, which has achieved good results. However, there is no consensus on the timing of LT and problems of nervous system damage and repair.

METHODS

We report the development of late-onset OTCD with central nervous system injury in an 11-year-old child who received liver transplantation at our transplant center. His first symptoms were nonprojectile vomiting, followed by irritability and disturbance of consciousness, after which the disease progressed rapidly and finally resulted in a coma. After liver transplantation, the child's consciousness returned to normal, muscle strength of the limbs gradually recovered from grade 0 to grade 4, and muscle tone gradually recovered from grade 4 to grade 1, suggesting that the motor nerves had gradually recovered. However, the child is currently mentally retarded, and the language center has not yet fully recovered.At the same time, we made a literature review of OTCD.

CONCLUSION

For OTCD patients with central nervous system injury, liver transplantation can fundamentally solve the problem of ammonia metabolism in the liver and avoids further damage to the central nervous system caused by hyperammonemia. At the same time, children's nervous systems are in the developmental stage when neuroplasticity is greatest. If liver transplantation is performed as soon as possible, nerve repair is still possible.

Variable disease manifestations and metabolic management within a single family affected by ornithine transcarbamylase deficiency

We report on a family with ornithine transcarbamylase (OTC) deficiency, an X-linked urea cycle disorder, with variable disease severity and tailored management strategies based on each family member's biochemical profile and clinical presentation. Our primary patient is a female monozygotic twin who presented to medical care at 10 months of age with acute liver failure, gastrointestinal symptoms, altered mental status, hypoglycemia, and hyperammonemia. The patient's older brother, known to have hemizygous OTC deficiency, died at 8 months of age from cardiac arrest after complications secondary to his diagnosis. Despite her family history, manifestation of symptoms of heterozygous (partial) OTC deficiency went unrecognized by multiple providers based on misconceptions regarding a female's risk for X-linked disease. Despite barriers related to the family's low socioeconomic status, follow-up care by a multidisciplinary metabolic care team, including moderate protein restriction and nitrogen scavenger therapy, led to positive outcomes for the patient. Her twin sister and mother are also heterozygous for variants in OTC and remain controlled on moderate protein restriction. This case illustrates the importance of genotyping all individuals with genetic risk factors for OTC deficiency and the variability in disease manifestation that necessitates tailored treatment approaches for individuals with partial OTC deficiency.

Benefits of tailored disease management in improving tremor, white matter hyperintensities, and liver enzymes in a child with heterozygous X-linked ornithine transcarbamylase deficiency

We report the case of a 19-month-old girl with late-onset ornithine transcarbamylase (OTC) deficiency initially referred to gastroenterology for intermittent vomiting lasting a year and abnormal liver enzymes (AST 730 U/L [reference range 26-55 U/L]; ALT 1213 U/L [reference range 11-30 U/L]) without hepatomegaly. While the patient was hospitalized for liver biopsy, intermittent tremors of the upper extremities with varying severity were noted. The patient was presumed to have hyperammonemia secondary to acute liver failure and was discharged after 5 days; follow-up monitoring led to readmission 7 days later. A brain MRI showed nonspecific bilateral pericallosal and bifrontal white matter FLAIR hyperintensities. These findings raised suspicion for a metabolic disease and prompted a genetics consultation. After inconclusive biochemical testing and worsening clinical status, rapid whole genome sequencing results were obtained identifying a novel, de novo, likely pathogenic, variant c.608C > T (p.Ser203Phe) in the OTC gene. The patient was promptly started on an oral nitrogen scavenger, citrulline supplementation, and protein restriction. Ammonia and glutamine levels normalized within 1 month of treatment and have stayed within the goal ranges with continued tailoring of treatment. Her parents noted resolution of vomiting and improved mood stability. Liver enzymes normalized after 2 months of treatment. The tremor, identified as asterixis, improved and a repeat brain MRI 3 months after the initial imaging showed near-complete resolution of previous white matter hyperintensities.

Glucagon Receptor Inhibition Reduces Hyperammonemia and Lethality in Male Mice with Urea Cycle Disorder

The liver plays a critical role in maintaining ammonia homeostasis. Urea cycle defects, liver injury, or failure and glutamine synthetase (GS) deficiency result in hyperammonemia, serious clinical conditions, and lethality. In this study we used a mouse model with a defect in the urea cycle enzyme ornithine transcarbamylase (Otcspf-ash) to test the hypothesis that glucagon receptor inhibition using a monoclonal blocking antibody will reduce the hyperammonemia and associated lethality induced by a high-protein diet, which exacerbates disease. We found reduced expression of glutaminase, which degrades glutamine and increased expression of GS in livers of Otcspf-ash mice treated with the glucagon receptor blocking antibody. The gene expression changes favor ammonia consumption and were accompanied by increased circulating glutamine levels and diminished hyperammonemia. Otcspf-ash mice treated with the glucagon receptor-blocking antibody gained lean and body mass and had increased survival. These data suggest that glucagon receptor inhibition using a monoclonal antibody could reduce the risk for hyperammonemia and other clinical manifestations of patients suffering from defects in the urea cycle, liver injury, or failure and GS deficiency.

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.

Integrated Multi-stakeholder Systems Thinking Strategy: Decision-making with Biopharmaceutics Risk Assessment Roadmap (BioRAM) to Optimize Clinical Performance of Drug Products

Decision-making in drug development benefits from an integrated systems approach, where the stakeholders identify and address the critical questions for the system through carefully designed and performed studies. Biopharmaceutics Risk Assessment Roadmap (BioRAM) is such a systems approach for application of systems thinking to patient focused and timely decision-making, suitable for all stages of drug discovery and development. We described the BioRAM therapy-driven drug delivery framework, strategic roadmap, and integrated risk assessment instrument (BioRAM Scoring Grid) in previous publications (J Pharm Sci 103:3377-97, 2014; J Pharm Sci 105:3243-55, 2016). Integration of systems thinking with pharmaceutical development, manufacturing, and clinical sciences and health care is unique to BioRAM where the developed strategy identifies the system and enables risk characterization and balancing for the entire system. Successful decision-making process in BioRAM starts with the Blueprint (BP) meetings. Through shared understanding of the system, the program strategy is developed and captured in the program BP. Here, we provide three semi-hypothetical examples for illustrating risk-based decision-making in high and moderate risk settings. In the high-risk setting, which is a rare disease area, two completely alternate development approaches are considered (gene therapy and small molecule). The two moderate-risk examples represent varied knowledge levels and drivers for the programs. In one moderate-risk example, knowledge leveraging opportunities are drawn from the manufacturing knowledge and clinical performance of a similar drug substance. In the other example, knowledge on acute tolerance patterns for a similar mechanistic pathway is utilized for identifying markers to inform the drug release profile from the dosage form with the necessary "flexibility" for dosing. All examples illustrate implementation of the BioRAM strategy for leveraging knowledge and decision-making to optimize the clinical performance of drug products for patient benefit.

Formulation and Clinical Evaluation of Sodium Benzoate Oral Solution for the Treatment of Urea Cycle Disorders in Pediatric Patients

BACKGROUND

Sodium benzoate, a common food preservative, is used in the treatment of patients with urea cycle disorders (UCDs) as it stimulates ammonia removal by a non-urea cycle-based pathway. Despite its use in the clinical routine, no commercially available oral formulations currently exist. Liquid formulation is normally well accepted in pediatric age and allows precise dosage according to the children's needs.

AIMS

(1) To prepare an oral sodium benzoate solution in different tastes and determine its stability, palatability, and tolerability and (2) to describe the long-term follow-up of two pediatric patients with UCDs treated with our formulation.

METHODS

We prepared five oral solutions of sodium benzoate (200 mg/ml) by adding different flavoring agents. We measured drug concentration in the samples by high-performance liquid chromatography (HPLC). We evaluated palatability and tolerability with adult volunteers. Long-term drug compliance and metabolic control were appraised in two pediatric patients.

RESULTS

All the oral solutions remained stable at room temperature along the 96-day test period, and they were well tolerated. The mint-flavored solution resulted the most palatable and preferred by adult volunteers. We report good drug compliance and good metabolic outcomes for both pediatric patients during the entire follow-up.

CONCLUSIONS

Our study highlighted the stability and tolerability of flavored sodium benzoate oral solutions. These solutions were well accepted during a long-term follow-up and guaranteed a good metabolic control. Since taste attributes are critical to ensure acceptable medication adherence in the pediatric age, flavored liquid formulations of sodium benzoate may be an efficient strategy to achieve therapeutic outcomes in UCD pediatric patients.

Suggested guidelines for the diagnosis and management of urea cycle disorders: First revision

In 2012, we published guidelines summarizing and evaluating late 2011 evidence for diagnosis and therapy of urea cycle disorders (UCDs). With 1:35 000 estimated incidence, UCDs cause hyperammonemia of neonatal (~50%) or late onset that can lead to intellectual disability or death, even while effective therapies do exist. In the 7 years that have elapsed since the first guideline was published, abundant novel information has accumulated, experience on newborn screening for some UCDs has widened, a novel hyperammonemia-causing genetic disorder has been reported, glycerol phenylbutyrate has been introduced as a treatment, and novel promising therapeutic avenues (including gene therapy) have been opened. Several factors including the impact of the first edition of these guidelines (frequently read and quoted) may have increased awareness among health professionals and patient families. However, under-recognition and delayed diagnosis of UCDs still appear widespread. It was therefore necessary to revise the original guidelines to ensure an up-to-date frame of reference for professionals and patients as well as for awareness campaigns. This was accomplished by keeping the original spirit of providing a trans-European consensus based on robust evidence (scored with GRADE methodology), involving professionals on UCDs from nine countries in preparing this consensus. We believe this revised guideline, which has been reviewed by several societies that are involved in the management of UCDs, will have a positive impact on the outcomes of patients by establishing common standards, and spreading and harmonizing good practices. It may also promote the identification of knowledge voids to be filled by future research.

Perspectives on urea cycle disorder management: Results of a clinician survey

BACKGROUND/AIMS

Urea cycle disorders (UCDs) are rare inborn errors of urea synthesis. US and European consensus statements on the diagnosis and treatment of UCDs were last published in 2001 and 2019, respectively. Recommendations are based primarily on case reports and expert opinion and there is limited agreement or consistency related to long-term management approaches. A clinician survey was conducted to assess current real-world practices and perspectives on challenges and unmet needs.

METHODS

A 14-item multiple-choice survey was administered to physicians in 2017. Clinicians who reported actively managing at least 1 patient with UCD were eligible to participate. Descriptive statistics were calculated for each survey item (frequencies for categorical variables; means, standard deviations, medians, and ranges for continuous variables).

RESULTS

Sixty-six US clinicians completed the survey (65 geneticists; 1 pediatric neurologist). Over 90% of responders agreed or strongly agreed that even modest elevations in ammonia could cause physiological and functional brain damage; >80% of respondents agreed that asymptomatic UCD patients are at risk of brain damage over time due to mild/subclinical elevations in ammonia. Eighty-six percent of clinicians agreed or strongly agreed with recommending genetic testing for female relatives when a patient is diagnosed with ornithine transcarbamylase deficiency. Ninety-four percent of respondents agreed that patients have better disease control when they are more adherent to their UCD therapy. Nearly 90% indicated that clinicians and patients would benefit from updated UCD management guidance. More than half (53%) of respondents rated the symptoms of UCDs as extremely or very burdensome to the everyday lives of patients and their families; only 8% rated UCD symptoms as slightly or not at all burdensome. The majority of clinicians agreed (48%) or strongly agreed (32%) that caring for a child or family member with a UCD has a negative impact on the quality of life and/or health of family members/guardians (e.g. stress, relationships, ability to work).

CONCLUSIONS

This self-reported survey suggests a need for updated and expanded clinical guidance on the long-term treatment and management of UCD patients.

Late-Onset Citrullinemia Type I: A Radiological Mimic of Herpes Encephalitis

We describe a 10 year old boy who presented with acute onset rapidly progressing encephalopathy. MRI revealed bilateral insular cortex and basifrontal involvement suggesting Herpes encephalitis.He was treated with acyclovir and his symptoms improved. Six months after the first hospitalization he reported back with two episodes of partial seizures. He was started on Valproate. A week after starting valproate he was readmitted with hyperammonemic encephalpathy, on further investigations Citrullinemia Type 1 was diagnosed. This case highlights a metabolic disorder which radiologically mimics herpes encephalitis. The management of the disorder differs remarkably from herpes encephalitis and hence its recognition and suspicion based on radiology is critical.

Influence of implementing a protocol for an intravenously administered ammonia scavenger on the management of acute hyperammonemia in a pediatric intensive care unit

The purpose of the study was to evaluate the influence of establishing a protocol for the use of combined sodium benzoate and sodium phenylacetate (SBSP) (Ammonul®) to treat acute hyperammonemia. This was a retrospective, single-center study in a 24-bed medical and surgical pediatric intensive care unit (PICU) in a tertiary care teaching maternal-child hospital in Canada. Inclusion criteria were age < 18 years, PICU admission between 1 January 2000 and 30 June 2016, and SBSP treatment. An SBSP delivery protocol was implemented in our hospital on 30 August 2008 in order to improve management of acute hyperammonemia. Patients were assigned to one of the two groups, without or with protocol, depending on date of admission. SBSP was ordered 34 times during the study period, and 23 orders were considered for analysis (14 with and 9 without protocol). Patient characteristics were similar between groups. The median time from diagnosis to prescription was significantly shorter in the protocol group [40 min (21-82) vs 100 min (70-150), p = 0.03)] but the median time from diagnosis to administration of the treatment was equivalent [144 min (90-220) vs 195 (143-274), (p = 0.2)]. Other clinical outcomes did not differ. This study is the first to compare two SBSP delivery strategies in the treatment of acute hyperammonemia in this PICU setting. Implementation of a delivery protocol shortened the time from diagnosis of hyperammonemia to prescription of SBSP and helped us identify other parameters that can be improved to optimize treatment delivery.

Food triggers and inherited metabolic disorders: a challenge to the pediatrician

Several disorders should be considered in the case of newborns and infants experiencing acute or recurrent symptoms after food ingestion. Immune-mediated adverse food reactions are the most frequent and always to be considered. Nevertheless, in the extensive differential diagnosis, clinicians should also include inherited metabolic disorders (IMDs).

This review reports clinical features and diagnostic aspects of the most common IMDs that may present with acute manifestations triggered by food intake. Major focus will be amino acid and protein metabolism defects and carbohydrate disorders.

Nowadays, for many of these disorders the risk of an acute presentation triggered by food has been decreased by the introduction of expanded newborn screening (NBS). Nevertheless, clinical suspicion remains essential because some IMDs do not have still reliable markers for NBS and a false negative screening result may occur.

The aim of this review is to help pediatricians to take these rare inherited disorders into account in the differential diagnosis of acute or recurrent gastrointestinal symptoms related to food intake, which may avoid delayed diagnosis and potentially life-threatening consequences.

Metabolomic profiling in umbilical venous plasma reveals effects of dietary rumen-protected arginine or N-carbamylglutamate supplementation in nutrient-restricted Hu sheep during pregnancy

Maternal nutrient restriction during pregnancy is a major problem worldwide for human and animal production. Arginine (Arg) is critical to health, growth and reproduction. N-carbamylglutamate (NCG), a key enzyme in arginine synthesis, is not extensively degraded in rumen. The aim of this study was to investigate ameliorating effects of rumen-protected arginine (RP-Arg) and NCG supplementation on dietary in undernourished Hu sheep during gestation. From day 35 to 110 of gestation, 32 Hu ewes carrying twin foetuses were randomly divided into four groups: a control (CG) group (n = 8; fed 100% National Research Council (NRC) requirements for pregnant sheep), a nutrient-restricted (RG) group (n = 8; fed 50% NRC requirements, which included 50% mineral-vitamin mixture) and two treatment (Arg and NCG) groups (n = 8; fed 50% NRC requirements supplemented with 20 g/day RP-Arg or 5 g/day NCG, which included 50% mineral-vitamin mixture). The umbilical venous plasma samples of foetus were tested by ¹ H-nuclear magnetic resonance. Thirty-two differential metabolites were identified, indicating altered metabolic pathways of amino acid, carbohydrate and energy, lipids and oxidative stress metabolism among the four groups. Our results demonstrate that the beneficial effect of dietary RP-Arg and NCG supplementation on mammalian reproduction is associated with complex metabolic networks.

Clinical course of 63 patients with neonatal onset urea cycle disorders in the years 2001-2013

BACKGROUND

Urea cycle disorders (UCDs) are rare inherited metabolic defects of ammonia detoxification. In about half of patients presenting with a UCD, the first symptoms appear within a few days after birth. These neonatal onset patients generally have a severe defect of urea cycle function and their survival and outcome prognoses are often limited. To understand better the current situation of neonatal onset in UCDs, we have performed a multicentre, retrospective, non-interventional case series study focussing on the most severe UCDs, namely defects of carbamoyl phosphate synthetase 1 (CPS1), ornithine transcarbamylase (OTC), and argininosuccinate synthetase (ASS).

METHODS AND RESULTS

Data of 63 patients were collected (27 patients with ASS deficiency, 23 patients with OTC deficiency, and 12 patients with CPS1 deficiency, one patient definite diagnosis not documented). The majority of patients (43/63, 68 %) had an initial ammonia concentration exceeding 500 μmol/L (normal < 100), of which most (26/43, 60.5 %) were also encephalopathic and were treated with hemodialysis. In patients surviving the initial crisis, recurrence of hyperammonemic events within the first 1.5 years of life occurred frequently (mean 3.6 events, range 0-20). Of all patients, 16 (25.4 %) died during or immediately after the neonatal period.

CONCLUSION

We observed in this cohort of neonatal onset UCD patients a high rate of initial life-threatening hyperammonemia and a high risk of recurrence of severe hyperammonemic crises. These corresponded to a high mortality rate during the entire study period (30.2 %) despite the fact that patients were treated in leading European metabolic centers. This underlines the need to critically re-evaluate the current treatment strategies in these patients.

High Protein Diet and Huntington's Disease

Huntington's disease (HD) is a neurodegenerative disorder caused by the huntingtin (HTT) gene with expanded CAG repeats. In addition to the apparent brain abnormalities, impairments also occur in peripheral tissues. We previously reported that mutant Huntingtin (mHTT) exists in the liver and causes urea cycle deficiency. A low protein diet (17%) restores urea cycle activity and ameliorates symptoms in HD model mice. It remains unknown whether the dietary protein content should be monitored closely in HD patients because the normal protein consumption is lower in humans (~15% of total calories) than in mice (~22%). We assessed whether dietary protein content affects the urea cycle in HD patients. Thirty HD patients were hospitalized and received a standard protein diet (13.7% protein) for 5 days, followed by a high protein diet (HPD, 26.3% protein) for another 5 days. Urea cycle deficiency was monitored by the blood levels of citrulline and ammonia. HD progression was determined by the Unified Huntington's Disease Rating Scale (UHDRS). The HPD increased blood citrulline concentration from 15.19 μmol/l to 16.30 μmol/l (p = 0.0378) in HD patients but did not change blood ammonia concentration. A 2-year pilot study of 14 HD patients found no significant correlation between blood citrulline concentration and HD progression. Our results indicated a short period of the HPD did not markedly compromise urea cycle function. Blood citrulline concentration is not a reliable biomarker of HD progression.

Adolescent presentations of inborn errors of metabolism

Several studies have shown that a large percentage of inborn errors of metabolism is present in adolescent patients. Individually, each diagnosis in this category of diseases is rare; therefore, there is often a significant delay in determining the etiology of a patient's complaints. These disorders can have a wide variety of multisystemic presentations, several of which overlap with more common disorders of adolescence. This review highlights the red-flag findings on history and physical examination indicating a possible inborn error of metabolism. In addition, a systematic approach for evaluating and categorizing these disorders is introduced and demonstrated through case examples. Primary care physicians play a crucial role in the early detection and prompt treatment of patients with late-onset inborn errors of metabolism.

Pediatric drug formulation of sodium benzoate extended-release granules

Urea cycle disorders are a group of inherited orphan diseases leading to hyperammonemia. Current therapeutic strategy includes high doses of sodium benzoate leading to three or four oral intakes per day. As this drug is currently available in capsules or in solution, children are either unable to swallow the capsule or reluctant to take the drug due to its strong bitter taste. The objective of the present study was to develop solid, multiparticulate formulations of sodium benzoate, which are suitable for pediatric patients (i.e. flavor-masked, easy to swallow and with a dosing system). Drug layering and coating in a fluidized bed were applied for preparing sustained-release granules. Two types of inert cores (GalenIQ® and Suglets®) and three different polymers (Kollicoat®, Aquacoat® and Eudragit®) were tested in order to select the most appropriate polymer and starter core for our purpose. Physical characteristics and drug release profiles of the pellets were evaluated. A Suglets® core associated with a Kollicoat® coating seems to be the best combination for an extended release of sodium benzoate. A curing period of 8 h was necessary to complete film formation and the resulting drug release pattern was found to be dependent of the acidity of the release medium.

Diagnostic and treatment implications of psychosis secondary to treatable metabolic disorders in adults: a systematic review

Objective

It is important for psychiatrists to be aware of certain inborn errors of metabolism (IEMs) as these rare disorders can present as psychosis, and because definitive treatments may be available for treating the underlying metabolic cause. A systematic review was conducted to examine IEMs that often present with schizophrenia-like symptoms.

Data sources

Published literature on MEDLINE was assessed regarding diseases of homocysteine metabolism (DHM; cystathionine beta-synthase deficiency [CbS-D] and homocysteinemia due to methyltetrahydrofolate reductase deficiency [MTHFR-D]), urea cycle disorders (UCD), acute porphyria (POR), Wilson disease (WD), cerebrotendinous-xanthomatosis (CTX) and Niemann-Pick disease type C (NP-C).

Study selection

Case reports, case series or reviews with original data regarding psychiatric manifestations and cognitive impairment published between January 1967 and June 2012 were included based on a standardized four-step selection process.

Data extraction

All selected articles were evaluated for descriptions of psychiatric signs (type, severity, natural history and treatment) in addition to key disease features.

Results

A total of 611 records were identified. Information from CbS-D (n = 2), MTHFR-D (n = 3), UCD (n = 8), POR (n = 12), WD (n = 11), CTX (n = 14) and NP-C publications (n = 9) were evaluated. Six non-systematic literature review publications were also included. In general, published reports did not provide explicit descriptions of psychiatric symptoms. The literature search findings are presented with a didactic perspective, showing key features for each disease and psychiatric signs that should trigger psychiatrists to suspect that psychotic symptoms may be secondary to an IEM.

Conclusion

IEMs with a psychiatric presentation and a lack of, or sub-clinical, neurological signs are rare, but should be considered in patients with atypical psychiatric symptoms.

Significant hepatic involvement in patients with ornithine transcarbamylase deficiency

OBJECTIVE

To determine the frequency of significant liver injury and acute liver failure (ALF) in patients with ornithine transcarbamylase deficiency (OTCD), the most common urea cycle defect.

STUDY DESIGN

In this historical cohort study, charts of 71 patients with OTCD at 2 centers were reviewed to assess the prevalence of ALF (international normalized ratio [INR] ≥2.0), liver dysfunction (INR 1.5-1.99), and hepatocellular injury (aspartate aminotransferase/alanine aminotransferase ≥250 IU/L).

RESULTS

More than one-half (57%) of the 49 patients with symptomatic OTCD had liver involvement; 29% met the criteria for ALF, 20% had liver dysfunction, and 8% had isolated hepatocellular injury. The prevalence of ALF was highest in the patients with more severe OTCD, including those with markedly elevated ammonia levels (>1000 μmol/L). Some patients with severe liver involvement (INR ≥2.0 and aspartate aminotransferase/alanine aminotransferase >1000 IU/L) had only moderate hyperammonemia (ammonia 100-400 μmol/L). ALF was the initial presenting symptom of OTCD in at least 3 of 49 symptomatic patients with OTCD.

CONCLUSION

Episodes of hepatocellular injury, liver dysfunction, and ALF were identified in a high proportion of children with symptomatic OTCD. The more severely affected patients had a higher likelihood of ALF. The diagnosis of a urea cycle defect should be considered in patients with unexplained ALF, liver dysfunction, or hepatocellular injury.

Late-onset ornithine transcarbamylase deficiency: treatment and outcome of hyperammonemic crisis

Hyperammonemic crises in ornithine transcarbamylase deficiency (OTC) can be associated with devastating cerebral edema resulting in severe long-term neurologic impairment and death. We present an 8-year-old boy who had late-onset OTC deficiency in which early and aggressive management of hyperammonemia and associated cerebral edema, including therapeutic hypothermia and barbiturate-induced coma, resulted in favorable neurologic outcome. Our patient presented with vomiting and altered mental status, and was found to have a significantly elevated serum ammonia level of 1561 μmol/L. Hyperammonemia was managed with hemodialysis, 10% sodium phenylacetate, 10% sodium benzoate, L-arginine, intravenous 10% dextrose, intralipids, and protein restriction. He developed significant cerebral edema with intracranial pressures >20 mm Hg, requiring treatment with 3% saline and mannitol. Despite this treatment our patient continued to have elevated intracranial pressures, which were treated aggressively with non-conventional modalities including therapeutic hypothermia, barbiturate-induced coma, and external ventricular drainage. This therapy resulted in stabilization of hyperammonemia and resolution of cerebral edema. Molecular testing later revealed a hemizygous mutation within the OTC gene. Neuropsychological testing 1 year after discharge showed normal intelligence with no visual-motor deficits, minor deficits in working memory and processing speed, and slightly below average processing speed and executive functioning.

Cross-sectional observational study of 208 patients with non-classical urea cycle disorders

Urea cycle disorders (UCDs) are inherited disorders of ammonia detoxification often regarded as mainly of relevance to pediatricians. Based on an increasing number of case studies it has become obvious that a significant number of UCD patients are affected by their disease in a non-classical way: presenting outside the newborn period, following a mild course, presenting with unusual clinical features, or asymptomatic patients with only biochemical signs of a UCD. These patients are surviving into adolescence and adulthood, rendering this group of diseases clinically relevant to adult physicians as well as pediatricians. In preparation for an international workshop we collected data on all patients with non-classical UCDs treated by the participants in 20 European metabolic centres. Information was collected on a cohort of 208 patients 50% of which were ≥ 16 years old. The largest subgroup (121 patients) had X-linked ornithine transcarbamylase deficiency (OTCD) of whom 83 were female and 29% of these were asymptomatic. In index patients, there was a mean delay from first symptoms to diagnosis of 1.6 years. Cognitive impairment was present in 36% of all patients including female OTCD patients (in 31%) and those 41 patients identified presymptomatically following positive newborn screening (in 12%). In conclusion, UCD patients with non-classical clinical presentations require the interest and care of adult physicians and have a high risk of neurological complications. To improve the outcome of UCDs, a greater awareness by health professionals of the importance of hyperammonemia and UCDs, and ultimately avoidance of the still long delay to correctly diagnose the patients, is crucial.

Ammonia toxicity to the brain

Hyperammonemia can be caused by various acquired or inherited disorders such as urea cycle defects. The brain is much more susceptible to the deleterious effects of ammonium in childhood than in adulthood. Hyperammonemia provokes irreversible damage to the developing central nervous system: cortical atrophy, ventricular enlargement and demyelination lead to cognitive impairment, seizures and cerebral palsy. The mechanisms leading to these severe brain lesions are still not well understood, but recent studies show that ammonium exposure alters several amino acid pathways and neurotransmitter systems, cerebral energy metabolism, nitric oxide synthesis, oxidative stress and signal transduction pathways. All in all, at the cellular level, these are associated with alterations in neuronal differentiation and patterns of cell death. Recent advances in imaging techniques are increasing our understanding of these processes through detailed in vivo longitudinal analysis of neurobiochemical changes associated with hyperammonemia. Further, several potential neuroprotective strategies have been put forward recently, including the use of NMDA receptor antagonists, nitric oxide inhibitors, creatine, acetyl-L-carnitine, CNTF or inhibitors of MAPKs and glutamine synthetase. Magnetic resonance imaging and spectroscopy will ultimately be a powerful tool to measure the effects of these neuroprotective approaches.

Urea cycle defects and hyperammonemia: effects on functional imaging

The urea-cycle disorders (UCDs) are a group of congenital enzyme and carrier deficiencies predisposing to hyperammonemia (HA). HA causes changes in the central nervous system (CNS) including alterations of neurotransmitter function, cell volume, and energy deprivation ultimately leading to cerebral edema. Neuropathological findings of UCDs primarily reflect changes in astrocyte morphology. Neurological features accompanying acute HA include changes in behavior and consciousness in the short term, and potential for impairments in memory and executive function as long-term effects. Plasma measures of ammonia and glutamine, although useful for clinical monitoring, prove poor markers of CNS function. Multimodal neuroimaging has potential to investigate impact on cognitive function by interrogating neural networks, connectivity and biochemistry. As neuroimaging methods become increasingly sophisticated, they will play a critical role in clinical monitoring and treatment of metabolic disease. We describe our findings in UCDs; with focus on Ornithine Transcarbamylase deficiency (OTCD) the only X linked UCD.

Hyperammonemia in children: on the crossroad of different disorders

BACKGROUND

Symptoms of hyperammonemia occur in patients irrespective of the kind of metabolic diseases. Age, metabolic and nutritional status, and decompensation factors such as infections influence clinical manifestations. Prolonged, untreated hyperammonemia leads to brain injury and intellectual disability. Treatment is directed at lowering plasma ammonia. Brain ammonium concentrations are 1.5 to 3.0 times higher than that in blood.

REVIEW SUMMARY

The authors discuss the pathophysiology of the symptoms and consequences of hyperammonemia in children, focusing on the metabolic disorders leading to an increased level of ammonia.

CONCLUSIONS

Ammonia toxicity has been investigated for a long time. According to the main hypotheses, the neurological alterations are connected to alterations in glutamatergic neurotransmission.

Children with autism spectrum disorders - the importance of medical investigations

BACKGROUND

Considerable knowledge about medical comorbidity in cases of Autism Spectrum Disorders (ASD) is available, still it is not well established how extensive the medical investigations should be in individual cases. The aim is to explore proportions of possible specific medical conditions in ASD.

METHODS

79 subjects went through extensive medical evaluations according to pre-defined procedures, including medical and developmental history, physical and biomedical investigations.

RESULTS

Clinical neurological findings were quite common, and we found a high number of pathological findings in the additional medical investigations. Our study revealed that these pathological deviations occurred more frequently in patients with childhood autism than in the other diagnostic sub-groups, the exception were chromosomal findings which occurred more often in patients not-diagnosed with childhood autism.

CONCLUSION

Medical and laboratory investigations should still be performed as a consequence of the patient's history, clinical presentations or family history. We should basically continue the use of non-routine and invasive procedures which do not put the patient at some unnecessary risk, in the absence of relevant clinical indications.

Recurrent somnolence in a 17-month-old infant: late-onset ornithine transcarbamylase (OTC) deficiency due to the novel hemizygous mutation c.535C > T (p.Leu179Phe)

Herein, we describe a case of a now 28-month-old boy who presented at the age of 17 months with four episodes of recurrent vomiting and somnolence during a period of four months with increasing severity. A comprehensive clinical and metabolic evaluation revealed normal blood pH and blood glucose, normal cerebral computed tomography and electroencephalogram but an elevated plasma ammonia concentration, which raised the suspicion of a urea cycle disorder. The combination of elevated urinary orotic acid and plasma glutamine with normal citrulline suggested the diagnosis of ornithine transcarbamylase (OTC) deficiency, which was confirmed by molecular genetic testing revealing the novel hemizygous mutation c.535C > T (p.Leu179Phe) of the OTC gene. After restitution of anabolism by administration of parenteral glucose, substitution of citrulline and detoxification of ammonia with sodium benzoate, the patient recovered rapidly and is in a stable metabolic and neurological state since then. This case underlines that the diagnosis of a urea cycle defect should be considered in the differential diagnosis of recurrent idiopathic vomiting in combination with unexplained neurological symptoms also beyond the neonatal period due to the possibility of mild or atypical late-onset presentation (e.g. OTC deficiency in hemizygous males).

Arginase deficiency with new phenotype and a novel mutation: contemporary summary

In areas without expanded newborn screening, instead of presenting neonatally, patients with arginase deficiency typically present with spastic paraplegia in early childhood. Diagnosis of this rare neurometabolic disease poses the first challenge because it is often misdiagnosed as cerebral palsy during initial stages. We describe arginase deficiency in a 20-year-old woman with spastic paraplegia, progressive dystonia, dementia, peripheral neuropathy, epilepsy, liver cirrhosis, and non-B/non-C hepatocellular carcinoma. A novel homozygous mutation NM_000045.2 (ARG1):c.673del (p.Arg225GlyfsX5) was detected. We suggest that all children presenting with progressive neurodegeneration or spastic paraplegia in the absence of risk factors for cerebral palsy should be screened for inborn errors of metabolism, including arginase deficiency. For monitoring urea cycle defects, noninvasive imaging screening for liver fibrosis and hepatocellular carcinoma can help ensure early detection, with potential treatment implications.

Early clinical manifestations and eating patterns in patients with urea cycle disorders

OBJECTIVES

To characterize dietary habits and eating patterns in patients with a urea cycle disorder (UCD), and to identify dietary habits that may serve as clues to lead to earlier diagnosis of these disorders.

STUDY DESIGN

This was a retrospective study of clinical and dietary data from hospital records of all patients with UCD (n = 90) attending the Royal Children's Hospital in Melbourne between 1972 and 2010.

RESULTS

Protein aversion, food refusal, frequent vomiting, poor appetite, and adverse reaction to high-protein-containing foods were documented in the majority of patients with available detailed dietary protein intake data. Fourteen of the 90 admissions for metabolic deterioration in which information regarding the precipitating factor(s) were available were directly related to protein intake (5 higher and 9 lower than prescribed).

CONCLUSION

Protein aversion is a common feature of UCD and may serve as a diagnostic clue in patients presenting with food refusal, recurrent vomiting, behavioral problems, mental retardation, and "unexplained" episodes of altered consciousness. Dietary history should be included in the investigation of these symptoms, which might lead to earlier diagnosis. Metabolic decompensation is more frequently related to low energy/protein intake than to high protein intake in these patients. Special attention should be given to protein aversion, which often leads to eating patterns that make it difficult for a patient to achieve the prescribed daily protein requirement.

Suggested guidelines for the diagnosis and management of urea cycle disorders

Urea cycle disorders (UCDs) are inborn errors of ammonia detoxification/arginine synthesis due to defects affecting the catalysts of the Krebs-Henseleit cycle (five core enzymes, one activating enzyme and one mitochondrial ornithine/citrulline antiporter) with an estimated incidence of 1:8.000. Patients present with hyperammonemia either shortly after birth (~50%) or, later at any age, leading to death or to severe neurological handicap in many survivors. Despite the existence of effective therapy with alternative pathway therapy and liver transplantation, outcomes remain poor. This may be related to underrecognition and delayed diagnosis due to the nonspecific clinical presentation and insufficient awareness of health care professionals because of disease rarity. These guidelines aim at providing a trans-European consensus to: guide practitioners, set standards of care and help awareness campaigns. To achieve these goals, the guidelines were developed using a Delphi methodology, by having professionals on UCDs across seven European countries to gather all the existing evidence, score it according to the SIGN evidence level system and draw a series of statements supported by an associated level of evidence. The guidelines were revised by external specialist consultants, unrelated authorities in the field of UCDs and practicing pediatricians in training. Although the evidence degree did hardly ever exceed level C (evidence from non-analytical studies like case reports and series), it was sufficient to guide practice on both acute and chronic presentations, address diagnosis, management, monitoring, outcomes, and psychosocial and ethical issues. Also, it identified knowledge voids that must be filled by future research. We believe these guidelines will help to: harmonise practice, set common standards and spread good practices with a positive impact on the outcomes of UCD patients.

Urea cycle disorders: brain MRI and neurological outcome

BACKGROUND

Urea cycle disorders encompass several enzyme deficiencies that can result in cerebral damage, with a wide clinical spectrum from asymptomatic to severe.

OBJECTIVE

The goal of this study was to correlate brain MRI abnormalities in urea cycle disorders with clinical neurological sequelae to evaluate whether MRI abnormalities can assist in guiding difficult treatment decisions.

MATERIALS AND METHODS

We performed a retrospective chart review of patients with urea cycle disorders and symptomatic hyperammonemia. Brain MRI images were reviewed for abnormalities that correlated with severity of clinical neurological sequelae.

RESULTS

Our case series comprises six urea cycle disorder patients, five with ornithine transcarbamylase deficiency and one with citrullinemia type 1. The observed trend in distribution of brain MRI abnormalities as the severity of neurological sequelae increased was the peri-insular region first, extending into the frontal, parietal, temporal and, finally, the occipital lobes. There was thalamic restricted diffusion in three children with prolonged hyperammonemia. Prior to death, this site is typically reported to be spared in urea cycle disorders.

CONCLUSION

The pattern and extent of brain MRI abnormalities correlate with clinical neurological outcome in our case series. This suggests that brain MRI abnormalities may assist in determining prognosis and helping clinicians with subsequent treatment decisions.

Hyperammonemic coma in an ornithine transcarbamylase mutation carrier following antepartum corticosteroids

Women who are carriers of the ornithine transcarbamylase (OTC) mutation are at risk for developing hyperammonemia during the postpartum period and at times of metabolic stress. We present a unique case of hyperammonemic coma occurring in an OTC mutation carrier during the antepartum period. Multiple factors, including the administration of antenatal corticosteroids, likely precipitated this critical condition. Clinicians should be aware of this life-threatening clinical presentation and be prepared to identify, treat, and prevent hyperammonemia in affected individuals.

Headache and neuropsychic disorders in the puerperium: a case report with suspected deficiency of urea cycle enzymes

An enzymatic abnormality of the urea cycle is a metabolic disorder occasionally seen in adults, but particularly in the puerperium. The main risk is acute hyperammoniemic encephalopathy, leading to psychosis, coma and even death if not diagnosed promptly and treated appropriately. Headache is frequent in the puerperium normally manifesting between 3 and 6 days after delivery. We describe here a 39-year-old woman, who 3 days after delivery presented diffuse tension-type headache and depression, followed by behavioral disorders, psychomotor agitation, epileptic seizures, and finally coma 2 days later. Pregnancy and normal delivery: routine blood chemistry findings, CT scan, MR imaging, angio-MR of the brain, and lumbar puncture were normal. EEG when seizures started, it showed diffuse slowing, as in the case of metabolic encephalopathy. This led us to assay blood ammonia, which was high at >400 mmol. Liver function and abdominal US were normal; hence, we suspected a urea cycle enzymatic abnormality, and requested for genetic tests. These confirmed a congenital primary metabolic deficiency of arginine succinate synthetase, with high citrullinemia (type II, adult form). Dialysis was started promptly, with initially iv arginine, then orally, plus medical therapy for the hyperammoniemia and a low protein diet; plasma ammonia dropped swiftly to normal, and her state of consciousness gradually improved until all the clinical symptoms had resolved. Ammonia assay should always be considered in the first few days of the puerperium in women with headache and behavioral disorders, to exclude an inborn deficiency of the urea cycle, which may have gone unnoticed until then.

Should metabolic diseases be systematically screened in nonsyndromic autism spectrum disorders?

Background

In the investigation of autism spectrum disorders (ASD), a genetic cause is found in approximately 10–20%. Among these cases, the prevalence of the rare inherited metabolic disorders (IMD) is unknown and poorly evaluated. An IMD responsible for ASD is usually identified by the associated clinical phenotype such as dysmorphic features, ataxia, microcephaly, epilepsy, and severe intellectual disability (ID). In rare cases, however, ASD may be considered as nonsyndromic at the onset of a related IMD.

Objectives

To evaluate the utility of routine metabolic investigations in nonsyndromic ASD.

Patients and Methods

We retrospectively analyzed the results of a metabolic workup (urinary mucopolysaccharides, urinary purines and pyrimidines, urinary creatine and guanidinoacetate, urinary organic acids, plasma and urinary amino acids) routinely performed in 274 nonsyndromic ASD children.

Results

The metabolic parameters were in the normal range for all but 2 patients: one with unspecific creatine urinary excretion and the other with persistent 3-methylglutaconic aciduria.

Conclusions

These data provide the largest ever reported cohort of ASD patients for whom a systematic metabolic workup has been performed; they suggest that such a routine metabolic screening does not contribute to the causative diagnosis of nonsyndromic ASD. They also emphasize that the prevalence of screened IMD in nonsyndromic ASD is probably not higher than in the general population (<0.5%). A careful clinical evaluation is probably more reasonable and of better medical practice than a costly systematic workup.

Ornithine transcarbamylase deficiency presenting as hepatitis

Ornithine transcarbamylase deficiency is an inborn error of metabolism that commonly presents as hyperammonemia in neonates. We present a case of a 2-year-old girl who was referred to a pediatric emergency department for evaluation of hepatitis, an uncommon presentation of ornithine transcarbamylase deficiency. Recognition of late presentations of this disease is important for survival and neurological outcome.

Genetic, structural and biochemical basis of carbamoyl phosphate synthetase 1 deficiency

Carbamoyl phosphate synthetase 1 (CPS1) plays a paramount role in liver ureagenesis since it catalyzes the first and rate-limiting step of the urea cycle, the major pathway for nitrogen disposal in humans. CPS1 deficiency (CPS1D) is an autosomal recessive inborn error which leads to hyperammonemia due to mutations in the CPS1 gene, or is caused secondarily by lack of its allosteric activator NAG. Proteolytic, immunological and structural data indicate that human CPS1 resembles Escherichia coli CPS in structure, and a 3D model of CPS1 has been presented for elucidating the pathogenic role of missense mutations. Recent availability of CPS1 expression systems also can provide valuable tools for structure-function analysis and pathogenicity-testing of mutations in CPS1. In this paper, we provide a comprehensive compilation of clinical CPS1 mutations, and discuss how structural knowledge of CPS enzymes in combination with in vitro analyses can be a useful tool for diagnosis of CPS1D.

Two hypomorphic alleles of mouse Ass1 as a new animal model of citrullinemia type I and other hyperammonemic syndromes

Citrullinemia type I (CTLN1, OMIM# 215700) is an inherited urea cycle disorder that is caused by an argininosuccinate synthetase (ASS) enzyme deficiency. In this report, we describe two spontaneous hypomorphic alleles of the mouse Ass1 gene that serve as an animal model of CTLN1. These two independent mouse mutant alleles, also described in patients affected with CTLN1, interact to produce a range of phenotypes. While some mutant mice died within the first week after birth, others survived but showed severe retardation during postnatal development as well as alopecia, lethargy, and ataxia. Notable pathological findings were similar to findings in human CTLN1 patients and included citrullinemia and hyperammonemia along with delayed cerebellar development, epidermal hyperkeratosis, and follicular dystrophy. Standard treatments for CTLN1 were effective in rescuing the phenotype of these mutant mice. Based on our studies, we propose that defective cerebellar granule cell migration secondary to disorganization of Bergmann glial cell fibers cause cerebellar developmental delay in the hyperammonemic and citrullinemic brain, pointing to a possible role for nitric oxide in these processes. These mouse mutations constitute a suitable model for both mechanistic and preclinical studies of CTLN1 and other hyperammonemic encephalopathies and, at the same time, underscore the importance of complementing knockout mutations with hypomorphic mutations for the generation of animal models of human genetic diseases.

[Ornithine transcarbamylase deficiency in adult]

INTRODUCTION

Ornithine transcarbamylase (OTC) deficiency is a X-linked inherited disorder characterized by hyperammoniemic encephalopathy in male neonates. However, there is an increased evidence of late-onset disease, including in adults.

CASE REPORTS

A 23-year-old woman presented with vomiting, somnolence, confusion and hyperammonemia. Familial history revealed OTC deficiency in three brothers and one sister, but urinary orotic acid level was normal at birth in the reported patient who therefore was considered as mutation-free. The mother was asymptomatic but had cognitive defect and moderate mental deficiency. Molecular biology demonstrated that both our patient and her mother were heterozygous for complete OCT deletion.

CONCLUSION

OCT deficiency could be diagnosed in adult patients at any age and clinical features are various, including hyperammonemic encephalopathy, psychiatric disorders or mental deficiency.

Highly variable clinical phenotype of carbamylphosphate synthetase 1 deficiency in one family: an effect of allelic variation in gene expression?

Deficiency of the urea cycle enzyme carbamylphosphate synthetase 1 (CPS1) causes hyperammonemia with a vast range of clinical severity from neonatal onset with early lethality to onset after age 40 with rare episodes of hyperammonemic confusion. The cause for this variability is not understood. We report two patients from one family with highly divergent clinical course, one presenting neonatally with a fatal form and the other at age 45 with benign diet-responsive disease. The patients are compound heterozygous for two mutations of the CPS1 gene, c.3558 + 1G > C and c.4101 + 2T > C. The haplotypes containing each mutation are identical between the two patients, as are the sequences of CPS1 exons and flanking introns. Transcriptional experiments show that the abnormal CPS1 transcripts generated by both mutations are identical in these two patients. We characterize promoter and enhancer sequences of the CPS1 gene and find also in these regions no sequence differences between patients. Finally, we perform cloning experiments and find that in the neonatal-onset case, clones of messenger RNA (mRNA) expressed from the allele carrying the c.4101 + 2T > C mutation are threefold more than clones of mRNA from the allele with the c.3558 + 1G > C mutation, whereas in the adult-onset case the two types of clones are equal, indicating skewed expression towards the c.4101 + 2T > C allele in the neonatal case. Although we are yet to understand the mechanism of this differential expression, our work suggests that allelic imbalance may explain clinical variability in CPS1 deficiency in some families.

Current concepts in the pathogenesis of urea cycle disorders

The common feature of urea cycle diseases (UCD) is a defect in ammonium elimination in liver, leading to hyperammonemia. This excess of circulating ammonium eventually reaches the central nervous system, where the main toxic effects of ammonium occur. These are reversible or irreversible, depending on the age of onset as well as the duration and the level of ammonium exposure. The brain is much more susceptible to the deleterious effects of ammonium during development than in adulthood, and surviving UCD patients may develop cortical and basal ganglia hypodensities, cortical atrophy, white matter atrophy or hypomyelination and ventricular dilatation. While for a long time, the mechanisms leading to these irreversible effects of ammonium exposure on the brain remained poorly understood, these last few years have brought new data showing in particular that ammonium exposure alters several amino acid pathways and neurotransmitter systems, cerebral energy, nitric oxide synthesis, axonal and dendritic growth, signal transduction pathways, as well as K(+) and water channels. All these effects of ammonium on CNS may eventually lead to energy deficit, oxidative stress and cell death. Recent work also proposed neuroprotective strategies, such as the use of NMDA receptor antagonists, nitric oxide inhibitors, creatine and acetyl-l-carnitine, to counteract the toxic effects of ammonium. Better understanding the pathophysiology of ammonium toxicity to the brain under UCD will allow the development of new strategies for neuroprotection.

Osmotic demyelination syndrome as a consequence of treating hyperammonemia in a patient with ornithine transcarbamylase deficiency

A 7-year-old female patient with a new diagnosis of ornithine transcarbamylase deficiency was treated for hyperammonemia with a standard protocol. Several days later, she developed ataxia, dysmetria, and dysarthria. Magnetic resonance imaging of the brain demonstrated pontine and extrapontine white matter changes consistent with osmotic demyelination. Classically described as a consequence of hyponatremia treatment, osmotic demyelination syndrome has rarely been associated with other entities. This case suggests a potentially serious complication of the standard therapy for hyperammonemia in patients with ornithine transcarbamylase deficiency.

[Ornithine transcarbamylase deficiency in adolescence and adulthood: first manifestation with life-threatening decompensation]

BACKGROUND

Ornithine transcarbamylase (OTC) deficiency is the most frequent innate disorder of the urea cycle and is X-chromosome linked. The disease normally manifests itself shortly after birth and is fatal when untreated. Due to the different expression and X-chromosomal inheritance the manifestation of symptoms can appear later particularly in girls and young women. The first symptoms are non-specific signs of elevated cerebral pressure as a result of a hyperammonemia, which range from nausea and headache up to cerebral herniation with fatal outcome. Measurement of plasma ammonia levels is a simple yet important screening test for patients with unexpected stupor or delirium.

CASE REPORTS

The two case reports show the clinical range from acute decompensation with acute cerebral herniation followed by fatal outcome to recovery under emergency therapy without substantial neurological deficits.

THERAPY

Emergency treatment consists of symptomatic securing of vital parameters and an immediate reduction in the ammonia level using high calorie, protein-free nutrition to avoid catabolism together with administration of arginine, benzoate or phenyl butyrate. In cases of coma with severe cerebral edema and the threat of a herniation reaction or excessive ammonia levels, emergency hemodialysis must be immediately carried out.

CONCLUSIONS

In the clinical routine it is extremely important to consider a metabolic defect at an early phase and among others to determine the ammonia level so that the appropriate treatment can be instigated in time.