Ornithine Transcarbamylase Research Articles

ODP284 Hyperinsulinism-Hyperammonaemia syndrome: a dive into the rare presentation and diagnostic challenges encountered in adults

Abstract Background Hyperinsulinemic-hyperammonemia, a rare form of congenital hyperinsulinemia, can seldom present in adulthood if failed to be diagnosed during infancy, enabling it to be difficult to identify, and predisposing affected individuals to neurological complications. Case A 20-year-old female with intellectual disability, seizure disorder and ornithine transcarbamylase deficiency was admitted for recurrent episodes of asymptomatic hypoglycemia. Her medications included risperidone, fluoxetine, levetiracetam, lacosamide, ferrous sulphate and acetaminophen. Physical examination including vital signs was unremarkable. Relevant labs included a fasting glucose of 46mg/dl [70-99]. Further work up of hypoglycemia revealed an IGF-1 of 215ng/dl [85-350] and AM Cortisol of 6.5mcg/dl [5-25]. Given a low AM cortisol level under stress, an ACTH stimulation test was done with appropriate response of cortisol of 24 following cosyntropin administration, ruling out adrenal insufficiency. The patient continued to have h ypoglycemia noted on several glucometer checks every 4 hours where she remained asymptomatic. She was further evaluated with a mixed meal study where no hypoglycemia was noted. A 72 -hour fast was performed which was terminated based on a venous blood sample glucose reading of 50 mg/dl confirmed after hypoglycemia was noted on a glucometer check. The labs showed elevated C-peptide levels of 4ng/ml [0.4-2], insulin of 4mIU/L [<25] and proinsulin level of 2.3pmol/l [3-20]. Levels of insulin and proinsulin were noted to be inappropriately normal in the setting of hypoglycemia. Beta hydroxybutyrate was low at 0.1mmol/L [<0.5] and glucagon inappropriately normal at 36pg/ml [50-100]. Sulfonylurea, meglitinide and autoimmune antibody screen were negative. CT abdomen and pelvis was negative for pancreatic abnormality. In the absence of evidence for acquired causes of hyperinsulinemic hypoglycemia, congenital cases were investigated. Based on that, further labs were obtained including ammonia levels which was elevated at 177.2 u/dl [15-45]. Accordingly, GLUD-1 gene mutation was sent, given high suspicion for hyperinsulinemic hyperammonemia syndrome, which resulted positive and confirmed the diagnosis. She was started on a protein restricted diet and diazoxide which regulated her blood glucose levels effectively. Discussion Hyperinsulinism/hyperammonemia (HI/HA) syndrome is a form of congenital hyperinsulinism caused by activating mutations of the GLUD 1 gene which encodes Glutamate Dehydrogenase, a key enzyme in the beta cell pathway of amino acid-stimulated insulin secretion. The resultant syndrome is characterized by fasting and protein induced hypoglycemia, elevated serum ammonia levels without typical hyperammonemic symptoms. Management includes effective blood glucose control with an insulin inhibitor such as diazoxide and a protein restricted diet with consideration to predominantly include carbohydrates and fat. Conclusion Hyperinsulinemia hyperammonemia is a rare form of congenital hyperinsulinemia typically diagnosed during infancy and should be considered as a possible differential diagnosis in patients presenting with new onset hypoglycemia, as timely diagnosis and intervention can prevent forthcoming neurological complications. Presentation: No date and time listed

Excretion of excess nitrogen and increased survival by loss of SLC6A19 in a mouse model of ornithine transcarbamylase deficiency.

Protein catabolism ultimately yields toxic ammonia, which must be converted to urea by the liver for renal excretion. In extrahepatic tissues, ammonia is temporarily converted primarily to glutamine for subsequent hepatic extraction. Urea cycle disorders (UCDs) are inborn errors of metabolism causing impaired ureagenesis, leading to neurotoxic accumulation of ammonia and brain glutamine. Treatment includes dietary protein restriction and oral "ammonia scavengers." These scavengers chemically combine with glutamine and glycine to yield excretable products, creating an alternate pathway of waste nitrogen disposal. The amino acid transporter SLC6A19 is responsible for >95% of absorption and reabsorption of free neutral amino acids in the small intestine and kidney, respectively. Genetic SLC6A19 deficiency causes massive neutral aminoaciduria but is typically benign. We hypothesized that inhibiting SLC6A19 would open a novel and effective alternate pathway of waste nitrogen disposal. To test this, we crossed SLC6A19 knockout (KO) mice with spfash mice, a model of ornithine transcarbamylase (OTC) deficiency. Loss of SLC6A19 in spfash mice normalized plasma ammonia and brain glutamine and increased median survival in response to a high protein diet from 7 to 97 days. While induced excretion of amino acid nitrogen is likely the primary therapeutic mechanism, reduced intestinal absorption of dietary free amino acids, and decreased muscle protein turnover due to loss of SLC6A19 may also play a role. In summary, the results suggest that SLC6A19 inhibition represents a promising approach to treating UCDs and related aminoacidopathies.

Three-Country Snapshot of Ornithine Transcarbamylase Deficiency.

X-linked ornithine transcarbamylase deficiency (OTCD) is the most common urea cycle defect. The disease severity ranges from asymptomatic carrier state to severe neonatal presentation with hyperammonaemic encephalopathy. We audited the diagnosis and management of OTCD, using an online 12-question-survey that was sent to 75 metabolic centres in Turkey, France and the UK. Thirty-nine centres responded and 495 patients were reported in total. A total of 208 French patients were reported, including 71 (34%) males, 86 (41%) symptomatic and 51 (25%) asymptomatic females. Eighty-five Turkish patients included 32 (38%) males, 39 (46%) symptomatic and 14 (16%) asymptomatic females. Out of the 202 UK patients, 66 (33%) were male, 83 (41%) asymptomatic and 53 (26%) symptomatic females. A total of 19%, 12% and 7% of the patients presented with a neonatal-onset phenotype in France, Turkey and the UK, respectively. Vomiting, altered mental status and encephalopathy were the most common initial symptoms in all three countries. While 69% in France and 79% in Turkey were receiving protein restriction, 42% were on a protein-restricted diet in the UK. A total of 76%, 47% and 33% of patients were treated with ammonia scavengers in Turkey, France and the UK, respectively. The findings of our audit emphasize the differences and similarities in manifestations and management practices in three countries.

A partial duplication of an X-linked gene exclusive of a primate lineage (Macaca)

Gene duplication plays a significant role in evolution. Paralogous gene copies may be lost due to the successive accumulation of deleterious mutations or remain active in the genome. In this work, a partial duplication of an X-linked region in the Macaca genus is identified and explored. Genomic comparisons reveal that the duplication encompasses the genes encoding ornithine transcarbamylase (OTC) and retinitis pigmentosa GTPase regulator (RPGR), spanning over 0.1 Mb on the chromosome 9 of Macaca. According to our analyses, the duplicated region of chromosome 9 involves partial coding sequences of both OTC and RPGR genes. Analyses of the selective pressures did not reveal significant differences in the ratio between nonsynonymous and synonymous mutations (w<1), suggesting that no selective pressures were acting in the evolutionary process. Reports for a biological role regarding some partial duplications exist in the literature, therefore, although being rare events, partial duplications of functionally important genes are worthy of study so that their impact can be explored.

Pathogenic variants of ornithine transcarbamylase deficiency: Nation-wide study in Japan and literature review.

Ornithine transcarbamylase deficiency (OTCD) is an X-linked disorder. Several male patients with OTCD suffer from severe hyperammonemic crisis in the neonatal period, whereas others develop late-onset manifestations, including hyperammonemic coma. Females with heterozygous pathogenic variants in the OTC gene may develop a variety of clinical manifestations, ranging from asymptomatic conditions to severe hyperammonemic attacks, owing to skewed lyonization. We reported the variants of CPS1, ASS, ASL and OTC detected in the patients with urea cycle disorders through a nation-wide survey in Japan. In this study, we updated the variant data of OTC in Japanese patients and acquired information regarding genetic variants of OTC from patients with OTCD through an extensive literature review. The 523 variants included 386 substitution (330 missense, 53 nonsense, and 3 silent), eight deletion, two duplication, one deletion-insertion, 55 frame shift, two extension, and 69 no category (1 regulatory and 68 splice site error) mutations. We observed a genotype–phenotype relation between the onset time (neonatal onset or late onset), the severity, and genetic mutation in male OTCD patients because the level of deactivation of OTC significantly depends on the pathogenic OTC variants. In conclusion, genetic information about OTC may help to predict long-term outcomes and determine specific treatment strategies, such as liver transplantation, in patients with OTCD.

Intrabiliary infusion of naked DNA vectors targets periportal hepatocytes in mice

Hydrodynamic tail vein injection (HTV) is the "gold standard" for delivering naked DNA vectors to mouse liver, thereby transfecting predominately perivenous hepatocytes. While HTV corrects metabolic liver defects such as phenylketonuria or cystathionine β-synthase deficiency, correction of spf ash mice with ornithine transcarbamylase (OTC) deficiency was not possible despite overexpression in the liver, as the OTC enzyme is primarily expressed in periportal hepatocytes. To target periportal hepatocytes, we established hydrodynamic retrograde intrabiliary injection (HRII) in mice and optimized minicircle (MC) vector delivery using luciferase as a marker gene. HRII resulted in a transfection efficiency below 1%, 100-fold lower than HTV. While HRII induced minimal liver toxicity compared with HTV, overexpression of luciferase by both methods, but not of a natural liver-specific enzyme, elicited an immune response that led to the elimination of luciferase expression. Further testing of MC vectors delivered via HRII in spf ash mice did not result in sufficient therapeutic efficacy and needs further optimization and/or selection of the corrected cells. This study reveals that luciferase expression is toxic for the liver. Furthermore, physical delivery of MC vectors via the bile duct has thepotential to treat defects restricted to periportal hepatocytes, which opens new doors for non-viral liver-directed gene therapy.

Predicting the disease severity in male individuals with ornithine transcarbamylase deficiency.

Ornithine transcarbamylase deficiency (OTC-D) is an X-linked metabolic disease and the most common urea cycle disorder. Due to high phenotypic heterogeneity, ranging from lethal neonatal hyperammonemic events to moderate symptoms and even asymptomatic individuals, the prediction of the disease course at an early disease stage is very important to individually adjust therapies such as medical treatment or liver transplantation. In this translational study, we developed a severity-adjusted classification system based on invitro residual enzymatic OTC activity. Applying a cell-based expression system, residual enzymatic OTC activities of 71 pathogenic OTC variants were spectrophotometrically determined and subsequently correlated with clinical and biochemical outcome parameters of 119 male individuals with OTC-D (mOTC-D) as reported in the UCDC and E-IMD registries. Integration of multiple data sources enabled the establishment of a robust disease prediction model for mOTC-D. Residual enzymatic OTC activity not only correlates with age at first symptoms, initial peak plasma ammonium concentration and frequency of metabolic decompensations but also predicts mortality. The critical threshold of 4.3% residual enzymatic activity distinguishes a severe from an attenuated phenotype. Residual enzymatic OTC activity reliably predicts the disease severity in mOTC-D and could thus serve as a tool for severity-adjusted evaluation of therapeutic strategies and counselling patients and parents.

When a normal newborn screen is not normal

Introduction: Ornithine Transcarbamylase (OTC) deficiency-an X-linked disorder-is the most common urea cycle defect in infancy and often presents with elevated ammonia.

S3154 Severe Noncirrhotic Hyperammonemia: What Urea-lly Should Consider

Introduction: Hyperammonemia is often the result of liver pathology. When hyperammonemia is not the result of liver disease, an occult disorder of metabolism must be on the differential for unexplained hyperammonemia, such as a urea cycle disorder (UCD). Case Description/Methods: A 57-year-old man with heart failure with recovered ejection fraction, atrial fibrillation, hypertension, and cervical neck fracture who had undergone a recent cervical spine corpectomy and fusion presented with worsening dysphagia and was found to have a cervical fluid collection for which he received a dexamethasone taper and a lumbar drain. He had no known underlying liver disease and denied significant alcohol history. He was later admitted to the intensive care unit (ICU) for unstable atrial fibrillation with rapid ventricular response (RVR). In the ICU, he became more somnolent and was unable to follow commands. Encephalopathy workup was significant for elevated BUN with normal creatinine, ammonia 772, and mildly elevated transaminases. His labs and imaging did not demonstrate cirrhosis or acute liver failure. Workup for inborn errors of metabolism showed mildly decreased citrulline. Urine and plasma amino acids were otherwise normal. His hyperammonemia resolved and his mentation improved with lactulose and rifaximin. UCD gene panel and further genetic workup is ongoing and to be continued outpatient. Discussion: Patients with elevations of ammonia present with encephalopathy, which may progress quickly to cerebral herniation. Survival requires immediate reduction of ammonia levels. Although the differential for hyperammonemia is broad, inborn errors of metabolism (IEM), like a UCD, should be considered when hyperammonemia is of unclear etiology. This patient’s liver workup revealed no findings consistent with cirrhosis or liver failure. Potential causes for his hyperammonemia include ischemic liver disease secondary to atrial fibrillation with RVR or degradation of blood products. IEMs may also be unmasked by steroid therapy, which is plausible in this patient who was on a steroid taper prior to his hyperammonemic state. Although IEMs often have early age of onset, UCDs have multiple modes of inheritance and can present at later stage. Ornithine transcarbamylase deficiency is the most common UCD and can present with reduced plasma citrulline in both kids and adults. Treatment for a potential IEM begins prior to confirmation of an etiology. Geneticists should be consulted early on for evaluation and management.

Clinical findings of patients with hyperammonemia affected by urea cycle disorders with hepatic encephalopathy.

Urea cycle disorders (UCD) are a group of genetic diseases caused by deficiencies in the enzymes and transporters involved in the urea cycle. The impairment of the cycle results in ammonia accumulation, leading to neurological dysfunctions and poor outcomes to affected patients. The aim of this study is to investigate and describe UCD patients' principal clinical and biochemical presentations to support professionals on urgent diagnosis and quick management, aiming better outcomes for patients. We explored medical records of 30 patients diagnosed in a referral center from Brazil to delineate UCD clinical and biochemical profile. Patients demonstrated a range of signs and symptoms, such as altered levels of consciousness, acute encephalopathy, seizures, progressive loss of appetite, vomiting, coma, and respiratory distress, in most cases combined with high levels of ammonia, which is an immediate biomarker, leading to a UCD suspicion. The most prevalent UCD detected were ornithine transcarbamylase deficiency, followed by citrullinemia type 1, hyperargininemia, carbamoyl phosphate synthase 1 deficiency, and argininosuccinic aciduria. Clinical symptoms were highly severe, being the majority developmental and neurological disabilities, with 20% of death rate. Laboratory analysis revealed high levels of ammonia (mean ± SD: 860 ± 470 μmol/L; reference value: ≤80 μmol/L), hypoglycemia, metabolic acidosis, and high excretion of orotic acid in the urine (except in carbamoyl phosphate synthetase 1 [CPS1] deficiency). We emphasize the need of urgent identification of UCD clinical and biochemical conditions, and immediate measurement of ammonia, to enable the correct diagnosis and increase the chances of patients' survival, minimizing neurological and psychomotor damage caused by hepatic encephalopathy.

Comparative structural insight into the unidirectional catalysis of ornithine carbamoyltransferases from Psychrobacter sp. PAMC 21119.

Ornithine carbamoyltransferases (OTCs) are involved in the arginine deiminase (ADI) pathway and in arginine biosynthesis. Two OTCs in a pair are named catalytic OTC (cOTC) and anabolic OTC (aOTC). The cOTC is responsible for catalyzing the third step of the ADI pathway to catabolize citrulline into carbamoyl phosphate (CP), as well as ornithine, and displays CP cooperativity. In contrast, aOTC catalyzes the biosynthesis of citrulline from CP and ornithine in vivo and is thus involved in arginine biosynthesis. Structural and biochemical analyses were employed to investigate the CP cooperativity and unidirectional function of two sequentially similar OTCs (32.4% identity) named Ps_cOTC and Ps_aOTC from Psychrobacter sp. PAMC 21119. Comparison of the trimeric structure of these two OTCs indicated that the 80s loop of Ps_cOTC has a unique conformation that may influence cooperativity by connecting the CP binding site and the center of the trimer. The corresponding 80s loop region of in Ps_aOTC was neither close to the CP binding site nor connected to the trimer center. In addition, results from the thermal shift assay indicate that each OTC prefers the substrate for the unidirectional process. The active site exhibited a blocked binding site for CP in the Ps_cOTC structure, whereas residues at the active site in Ps_aOTC established a binding site to facilitate CP binding. Our data provide novel insights into the unidirectional catalysis of OTCs and cooperativity, which are distinguishable features of two metabolically specialized proteins.

A complex case of delayed diagnosis of ornithine transcarbamylase deficiency in an adult patient with multiple comorbidities

We report the case of a medically complex African American adult female with ornithine transcarbamylase (OTC) deficiency diagnosed after lifelong protein aversion and new onset of chronic vomiting and abdominal pain with intermittent lethargy and confusion. Symptomatology was crucial to diagnosis as genetic testing did not identify any pathogenic variants in OTC; however, the patient's diagnosis was delayed despite her having longstanding symptoms of a urea cycle disorder (UCD). Her symptoms improved after treatment with a modified protein-restricted diet, long-term nitrogen-scavenger therapy, and supplemental L-citrulline. Adherence to her UCD management regimen remained a challenge due to her underlying frailty and other medical conditions, which included primary renal impairment (further exasperated by type 2 diabetes mellitus) and decreased left-ventricular function. She passed away 3 years after her OTC deficiency diagnosis due to complications of congestive heart failure. Her OTC deficiency did not have a major impact on her final illness, and appropriate OTC deficiency management was provided until the decision was made to withdraw medical care.

Effects and mechanism of diammonium glycyrrhizinate on liver injury in severely scalded rats

Objective: To investigate the effects and mechanism of diammonium glycyrrhizinate (DG) on liver injury in severely scalded rats. Methods: The experimental research method was used. Fifty-four female Sprague-Dawley rats aged 7-9 weeks were divided into sham injury group with simulated injury on the back, and simple scald group and scald+DG group with scald of 30% total body surface area on the back, with 18 rats in each group. Rats in sham injury group were not specially treated after injury, and rats in simple scald group and scald+DG group were rehydrated for antishock. Besides, rats in scald+DG group were injected intraperitoneally with 50 mg/kg DG at post injury hour (PIH) 1, 25, and 49. Rats in the three groups were collected, the serum content of liver function injury related indexes including aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), total protein, and albumin was measured by automatic biochemical assay analyzer, and serum content of ornithine carbamoyl transferase (OCT) was measured by enzyme-linked immunosorbent assay method at PIH 24, 48, and 72; hepatic histopathological changes at PIH 72 were observed by hematoxylin-eosin staining; the mRNA expressions of B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein (Bax), glucose regulated protein 78 (GRP78), activating transcription factor 4 (ATF4), and protein kinase R-like endoplasmic reticulum kinase (PERK) in liver tissue were detected by real-time fluorescent quantitative reverse transcription polymerase chain reaction at PIH 24, 48, and 72. The protein expressions of Bcl-2, Bax, GRP78, PERK, and ATF4 in liver tissue were detected by Western blotting at PIH 72 in sham injury group and PIH 24, 48, and 72 in simple scald group and scald+DG group. The number of samples was 6 in each group at each time point. Data were statistically analyzed with analysis of variance for factorial design, one-way analysis of variance, and Bonferroni test. Results: Compared with that in sham injury group, the serum content of AST, ALT, and LDH was significantly increased (P<0.01), and the serum content of total protein and albumin was significantly decreased (P<0.05 or P<0.01) of rats in simple scald group at all post-injury time points. Compared with those in simple scald group, the serum AST content of rats in scald+DG group at PIH 24 was decreased significantly (P<0.05); the serum AST, ALT, and LDH content of rats in scald+DG group at PIH 48 was decreased significantly (P<0.01), and the serum total protein content was increased significantly (P<0.01); the serum AST, ALT, and LDH content of rats in scald+DG group at PIH 72 was decreased significantly (P<0.01), and the serum total protein and albumin content was increased significantly (P<0.01). At PIH 24, 48, and 72, the serum OCT content of rats in simple scald group was (48.5±3.9), (40.8±2.4), and (38.7±2.0) U/L, which was significantly higher than (15.1±2.5), (15.7±2.6), and (16.4±3.7) U/L in sham injury group (P<0.01), and (39.0±4.5), (31.8±2.0), and (22.1±2.6) U/L in scald+DG group (P<0.05 or P<0.01). At PIH 72, the cells in liver tissue of rats in sham injury group had normal morphology and regular arrangement, with no obvious inflammatory cell infiltration; the cells in liver tissue of rats in simple scald group had disordered arrangement, diffuse steatosis, and moderate inflammatory cell infiltration; the cells in liver tissue of rats in scald+DG group arranged regularly, with scattered steatosis and a small amount of inflammatory cell infiltration. Compared with those in sham injury group, the Bcl-2 mRNA (P<0.05 or P<0.01) and protein expressions of liver tissue were significantly decreased, and the mRNA (P<0.01) and protein expressions of Bax were significantly increased in rats in simple scald group at PIH 24, 48, and 72. Compared with those in simple scald group, the mRNA (P<0.05) and protein expressions of Bax in liver tissue of rats in scald+DG group were decreased significantly at PIH 48; the mRNA (P<0.01) and protein expressions of Bax in liver tissue of rats in scald+DG group were significantly decreased, and the mRNA (P<0.01) and protein expressions of Bcl-2 were significantly increased at PIH 72. Compared with those in sham injury group, the mRNA (P<0.05 or P<0.01) and protein expressions of ATF4, GRP78, and PERK in liver tissue were significantly increased in rats in simple scald group at all post-injury time points. Compared with those in simple scald group, the mRNA (P<0.01) and protein expressions of ATF4 in liver tissue of rats in scald+DG group at PIH 48 were significantly decreased, and the mRNA (P<0.05 or P<0.01) and protein expressions of ATF4, GRP78, and PERK were significantly decreased in liver tissue of rats in scald+DG group at PIH 72. Conclusions: DG can effectively reduce the degree of liver injury in rats after severe scald, and the mechanism may involve alleviating endoplasmic reticulum stress and mitigating mitochondrial damage.

Clinical Characteristics of Pediatric Patients with Urea Cycle Disorders

Objective: Urea cycle disorders (UCDs) are inherited deficiencies of the enzymes or transport molecules involved in the cellular excretion of excess ammonia produced during protein metabolism. The aim of this study was to evaluate the clinical characteristics and long-term outcome of pediatric patients with UCDs. Material and Methods: Our research was conducted between September 2020-March 2021 in Dr. Sami Ulus Maternity and Child Health Training and Research Hospital. Clinical characteristics in 16 patients with UCDs [carbamoyl phosphate synthetase I deficiency (n=1), N-acetylglutamate synthase deficiency(n=1), argininosuccinate lyase deficiency (n=4), argininosuccinate synthetase deficiency (n=4), arginase deficiency (n=2), ornithine transcarbamylase deficiency (n=2), hyperammonemia hyperornithinemia homocitrullinuria syndrome (n=2)] were defined. The term “neonatal-onset” UCD was used if symptoms occurred within 28 days of life, and “late-onset” if symptoms started after the neonatal period. Results: Eight patients presented with acute metabolic crisis during newborn period. Core clinical phenotype in neonatal-onset UCDs included sepsis-like findings, whereas epilepsy and mental retardation was predominant in lateonset UCDs. For patients with neonatal-onset UCDs, hyperammonemia was more severe at the initial period. Conclusion: Despite evolving treatment opportunities, still high mortality rates were found in neonatal-onset UCD. UCDs should be suspected in pediatric patients with hyperammonemia and metabolic investigations should be performed immediately to enlighten diagnosis. Neonatal-onset UCD usually present with symptoms of acute hyperammonemia, while moresubtle neurological manifestations are frequent initial findings in the late onset UCD.

Moving towards a novel therapeutic strategy for hyperammonemia that targets glutamine metabolism.

Patients with urea cycle disorders intermittently develop episodes of decompensation with hyperammonemia. Although such an episode is often associated with starvation and catabolism, its molecular basis is not fully understood. First, we attempted to elucidate the mechanism of such starvation-associated hyperammonemia. Using a mouse embryonic fibroblast (MEF) culture system, we found that glucose starvation increases ammonia production, and that this increase is associated with enhanced glutaminolysis. These results led us to focus on α-ketoglutarate (AKG), a glutamate dehydrogenase inhibitor, and a major anaplerotic metabolite. Hence, we sought to determine the effect of dimethyl α-ketoglutarate (DKG), a cell-permeable AKG analog, on MEFs and found that DKG mitigates ammonia production primarily by reducing flux through glutamate dehydrogenase. We also verified that DKG reduces ammonia in an NH4 Cl-challenged hyperammonemia mouse model and observed that DKG administration reduces plasma ammonia concentration to 22.8% of the mean value for control mice that received only NH4 Cl. In addition, we detected increases in ornithine concentration and in the ratio of ornithine to arginine following DKG treatment. We subsequently administered DKG intravenously to a newborn pig with hyperammonemia due to ornithine transcarbamylase deficiency and found that blood ammonia concentration declined significantly over time. We determined that this effect is associated with facilitated reductive amination and glutamine synthesis. Our present data indicate that energy starvation triggers hyperammonemia through enhanced glutaminolysis and that DKG reduces ammonia accumulation via pleiotropic mechanisms both in vitro and in vivo. Thus, cell-permeable forms of AKG are feasible candidates for a novel hyperammonemia treatment.

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.

Roles of lncRNA LVBU in regulating urea cycle/polyamine synthesis axis to promote colorectal carcinoma progression

Altered expression of Urea Cycle (UC) enzymes occurs in many tumors, resulting a metabolic hallmark termed as UC dysregulation. Polyamines are synthesized from ornithine, and polyamine synthetic genes are elevated in various tumors. However, the underlying deregulations of UC/ polyamine synthesis in cancer remain elusive. Here, we characterized a hypoxia-induced lncRNA LVBU (lncRNA regulation via BCL6/urea cycle) that is highly expressed in colorectal cancer (CRC) and correlates with poor cancer prognosis. Increased LVBU expression promoted CRC cells proliferation, foci formation and tumorigenesis. Further, LVBU regulates urea cycle and polyamine synthesis through BCL6, a negative regulator of p53. Mechanistically, overexpression of LVBU competitively bound miR-10a/miR-34c to protect BCL6 from miR-10a/34c-mediated degradation, which in turn allows BCL6 to block p53-mediated suppression of genes (arginase1 ARG1, ornithine transcarbamylase OTC, ornithine decarboxylase 1 ODC1) involved in UC/polyamine synthesis. Significantly, ODC1 inhibitor attenuated the growth of patient derived xenografts (PDX) that sustain high LVBU levels. Taken together, elevated LVBU can regulate BCL6-p53 signaling axis for systemic UC/polyamine synthesis reprogramming and confers a predilection toward CRC development. Our data demonstrates that further drug development and clinical evaluation of inhibiting UC/polyamine synthesis are warranted for CRC patients with high expression of LVBU.

Considerations for prenatal and postpartum management of a female patient with ornithine transcarbamylase deficiency

We report on pregnancy management and outcomes in a 27-year-old female patient with ornithine transcarbamylase (OTC) deficiency, the most common inherited enzyme deficiency in the urea cycle. Our patient was diagnosed during childhood after hyperammonemia associated with surgery and steroid treatment and was well-controlled with nitrogen scavenger treatment, low-protein diet, and L-citrulline supplementation. OTC gene sequencing identified a variant of unknown significance that has more recently been classified as likely pathogenic. Women with OTC deficiency are at increased risk of hyperammonemia during pregnancy and the postpartum period, therefore monthly follow up and laboratory assessments are critical in management decision making. Our patient was maintained on glycerol phenylbutyrate, L-citrulline and essential amino acid supplements, along with restricted protein intake during pregnancy. A multidisciplinary approach with the obstetrics, prenatal genetics, high risk obstetric, and anesthesia teams was also necessary for optimal management during pregnancy, throughout labor and delivery, and during the postpartum period. After successful childbirth and discharge, our patient experienced a hyperammonemic crisis related to poor enteral nutrition, and acute management protocols were implemented to stabilize her. For her newborn son, acute hyperammonemia protocols were on standby, and newborn screening and laboratory testing were expedited to assess his risk. He was healthy and did not experience symptoms of concern. In this case report, we emphasize the importance of close collaboration with maternal-fetal medicine team members during and immediately after pregnancy to ensure successful management of a female patient with OTC deficiency and her newborn.

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.

Ornithine transcarbamylase deficiency: A diagnostic odyssey

Ornithine transcarbamylase deficiency: A diagnostic odyssey