Unraveling the Link: Seizure Characteristics and Ammonia Levels in Urea Cycle Disorder During Hyperammonemic Crises.

BACKGROUND: This retrospective clinical study performed at a single clinical center aimed to identify the prevalence of seizures in individuals with urea cycle disorders (UCDs) with and without hyperammonemic (HA) crises. In addition, we sought to correlate the utility of biochemical markers and electroencephalography (EEG) in detecting subclinical seizures during HA. METHODS: Medical records of individuals with UCDs enrolled in Urea Cycle Disorders Consortium Longitudinal Study (UCDC-LS) (NCT00237315) at Children's National Hospital between 2006 and 2022 were reviewed for evidence of clinical and subclinical seizuress during HA crises, and initial biochemical levels concurrently. RESULTS: Eighty-five individuals with UCD were included in the analyses. Fifty-six of the 85 patients (66%) experienced HA crises, with a total of 163 HA events. Seizures are observed in 13% of HA events. Among all HA events with concomitant EEG, subclinical seizures were identified in 27% of crises of encephalopathy without clinical seizures and 53% of crises with clinical seizures. The odds of seizures increases 2.65 (95% confidence interval [CI], 1.51 to 4.66) times for every 100 µmol/L increase in ammonia and 1.14 (95% CI, 1.04 to 1.25) times for every 100 µmol/L increase in glutamine. CONCLUSIONS: This study highlights the utility of EEG monitoring during crises for patients presenting with clinical seizures or encephalopathy with HA. During HA events, measurement of initial ammonia and glutamine can help determine risk for seizures and guide EEG monitoring decisions.

Citrin-deficient patient-derived induced pluripotent stem cells as a pathological liver model for congenital urea cycle disorders.

Citrin deficiency is a congenital secondary urea cycle disorder lacking useful disease models for effective treatment development. In this study, human induced pluripotent stem cells (iPSCs) were generated from two patients with citrin deficiency and differentiated into hepatocyte-like cells (HLCs). Citrin-deficient HLCs produced albumin and liver-specific markers but completely lacked citrin protein and expressed argininosuccinate synthase only weakly. In addition, ammonia concentrations in a medium cultured with citrin-deficient HLCs were higher than with control HLCs. Sodium pyruvate administration significantly reduced ammonia concentrations in the medium of citrin-deficient HLCs and slightly reduced ammonia in HLCs differentiated from control iPSCs, though this change was not significant. Our results suggest that sodium pyruvate may be an efficient treatment for patients with citrin deficiency. Citrin-deficient iPSCs are a pathological liver model for congenital urea cycle disorders to clarify pathogenesis and develop novel therapies.

Postoperative hyperammonemic encephalopathy due to unexpected constipation in a patient with hyperornithinemia-hyperammonemia-homocitrullinuria syndrome: a case report.

BACKGROUND: Hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome is a rare autosomal recessive urea cycle disorder associated with a high risk of exacerbation of hyperammonemia during the perioperative period. Here, we describe an adult patient with HHH syndrome who developed hyperammonemic encephalopathy secondary to postoperative constipation. CASE PRESENTATION: A 52-year-old patient with HHH syndrome underwent intrathecal baclofen pump insertion for lower limb spasticity under general anesthesia. The surgery was uneventful, without any increase in serum ammonia levels. However, after surgery, he was constipated, and on postoperative day (POD) 3, he fell into a coma with an exacerbation of hyperammonemia (894 µg/dL). After administering a glycerin enema, he defecated, leading to a rapid decrease in serum ammonia levels to 165 µg/dL. He regained consciousness, and serum ammonia levels remained stable as long as he defecated. CONCLUSIONS: We suggest strict management of defecation during the perioperative period to prevent hyperammonemia in patients with HHH syndrome.

[Treatment of ornithine transcarbamylase deficiency in a child with glyceryl phenylbutyrate]. / è‹¯ä¸é ¸ç”˜æ²¹é ¯æ²»ç–—å„¿ç«¥é¸Ÿæ°¨é ¸æ°¨ç”²é °åŸºè½¬ç§»é ¶ç¼ºä¹ç—‡1例.

Glyceryl phenylbutyrate (GPB) serves as a long-term management medication for Ornithine transcarbamylase deficiency (OTCD), effectively controlling hyperammonemia, but there is a lack of experience in using this medicine in China. This article retrospectively analyzes the case of a child diagnosed with OTCD at Shanghai Children's Medical Center, Shanghai Jiao Tong University School of Medicine, including a review of related literature. After diagnosis, the patient was treated with GPB, followed by efficacy follow-up and pharmacological monitoring. The 6-year and 6-month-old male patient exhibited poor speech development, disobedience, temper tantrums, and aggressive behavior. Blood ammonia levels peaked at 327 µmol/L; urine organic acid analysis indicated elevated uracil levels; cranial MRI showed extensive abnormal signals in both cerebral hemispheres. Genetic testing revealed de novo mutation in the OTC gene (c.241T>C, p.S81P). Blood ammonia levels were approximately 43, 80, and 56 µmol/L at 1, 2, and 3 months after starting GPB treatment, respectively. During treatment, blood ammonia was well-controlled without drug-related adverse effects. The patient showed improvement in developmental delays, obedience, temperament, and absence of aggressive behavior.

The efficacy of Carbamylglutamate impacts the nutritional management of patients with N-Acetylglutamate synthase deficiency.

BACKGROUND: The autosomal recessive disorder N-acetylglutamate synthase (NAGS) deficiency is the rarest defect of the urea cycle, with an incidence of less than one in 2,000,000 live births. Hyperammonemic crises can be avoided in individuals with NAGS deficiency by the administration of carbamylglutamate (also known as carglumic acid), which activates carbamoyl phosphatase synthetase 1 (CPS1). The aim of this case series was to introduce additional cases of NAGS deficiency to the literature as well as to assess the role of nutrition management in conjunction with carbamylglutamate therapy across new and existing cases. METHODS: We conducted retrospective chart reviews of seven cases of NAGS deficiency in the US and Canada, focusing on presentation, diagnosis, medication management, nutrition management, and outcomes. RESULTS: Five new and two previously published cases were included. Presenting symptoms were consistent with previous reports. Diagnostic confirmation via molecular testing varied in protocol across cases, with consecutive single gene tests leading to long delays in diagnosis in some cases. All patients responded well to carbamylglutamate therapy, as indicated by normalization of plasma ammonia and citrulline, as well as urine orotic acid in patients with abnormal levels at baseline. Although protein restriction was not prescribed in any cases after carbamylglutamate initiation, two patients continued to self-restrict protein intake. One patient experienced two episodes of hyperammonemia that resulted in poor long-term outcomes. Both episodes occurred after a disruption in access to carbamylglutamate, once due to insurance prior authorization requirements and language barriers and once due to seizure activity limiting the family's ability to administer carbamylglutamate. CONCLUSIONS: Follow-up of patients with NAGS deficiency should include plans for illness and for disruption of carbamylglutamate access, including nutrition management strategies such as protein restriction. Carbamylglutamate can help patients with NAGS deficiency to liberalize their diets, but the maximum safe level of protein intake to prevent hyperammonemia is not yet known. Patients using this medication should still monitor their diet closely and be prepared for any disruptions in medication access, which might require immediate dietary adjustments or medical intervention to prevent hyperammonemia.

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

BACKGROUND: Ornithine transcarbamylase deficiency (OTCD) due to an X-linked OTC mutation, is responsible for moderate to severe hyperammonemia (HA) with substantial morbidity and mortality. About 80% of females with OTCD remain apparently "asymptomatic" with limited studies of their clinical characteristics and long-term health vulnerabilities. Multimodal neuroimaging studies and executive function testing have shown that asymptomatic females exhibit limitations when stressed to perform at higher cognitive load and had reduced activation of the prefrontal cortex. This retrospective study aims to improve understanding of factors that might predict development of defined complications and serious illness in apparent asymptomatic females. A proband and her daughter are presented to highlight the utility of multimodal neuroimaging studies and to underscore that asymptomatic females with OTCD are not always asymptomatic. METHODS: We review data from 302 heterozygote females with OTCD enrolled in the Urea Cycle Disorders Consortium (UCDC) longitudinal natural history database. We apply multiple neuroimaging modalities in the workup of a proband and her daughter. RESULTS: Among the females in the database, 143 were noted as symptomatic at baseline (Sym). We focused on females who were asymptomatic (Asx, n = 111) and those who were asymptomatic initially upon enrollment in study but who later became symptomatic sometime during follow-up (Asx/Sym, n = 22). The majority of Asx (86%) and Asx/Sym (75%) subjects did not restrict protein at baseline, and ~38% of Asx and 33% of Asx/Sym subjects suffered from mild to severe neuropsychiatric conditions such as mood disorder and sleep problems. The risk of mild to severe HA sometime later in life for the Asx and Asx/Sym subjects as a combined group was ~4% (5/133), with ammonia ranging from 77 to 470 µM and at least half (2/4) of subjects requiring hospital admission and nitrogen scavenger therapy. For this combined group, the median age of first HA crisis was 50 years, whereas the median age of first symptom which included neuropsychiatric and/or behavioral symptoms was 17 years. The multimodal neuroimaging studies in female heterozygotes with OTCD also underscore that asymptomatic female heterozygotes with OTCD (e.g., proband) are not always asymptomatic. CONCLUSIONS: Analysis of Asx and Asx/Sym females with OTCD in this study suggests that future evidence-based management guidelines and/or a clinical risk score calculator for this cohort could be useful management tools to reduce morbidity and improve long-term quality of life.

Efficacy and safety of pegzilarginase in arginase 1 deficiency (PEACE): a phase 3, randomized, double-blind, placebo-controlled, multi-centre trial.

Background: Arginase 1 Deficiency (ARG1-D) is a rare debilitating, progressive, inherited, metabolic disease characterized by marked increases in plasma arginine (pArg) and its metabolites, with increased morbidity, substantial reductions in quality of life, and premature mortality. Effective treatments that can lower arginine and improve clinical outcomes is currently lacking. Pegzilarginase is a novel human arginase 1 enzyme therapy. The present trial aimed to demonstrate efficacy of pegzilarginase on pArg and key mobility outcomes. Methods: This Phase 3 randomized, double-blind, placebo-controlled, parallel-group clinical trial (clinicaltrials.govNCT03921541, EudraCT 2018-004837-34), randomized patients with ARG1-D 2:1 to intravenously/subcutaneously once-weekly pegzilarginase or placebo in conjunction with their individualized disease management. It was conducted in 7 countries; United States, United Kingdom, Canada, Austria, France, Germany, Italy. Primary endpoint was change from baseline in pArg after 24 weeks; key secondary endpoints were change from baseline at Week 24 in Gross Motor Function Measure part E (GMFM-E) and 2-min walk test (2MWT). Full Analysis Set was used for the analyses. Findings: From 01 May 2019 to 29 March 2021, 32 patients were enrolled and randomized (pegzilarginase, n = 21; placebo, n = 11). Pegzilarginase lowered geometric mean pArg from 354.0 µmol/L to 86.4 µmol/L at Week 24 vs 464.7 to 426.6 µmol/L for placebo (95% CI: -67.1%, -83.5%; p < 0.0001) and normalized levels in 90.5% of patients (vs 0% with placebo). In addition, clinically relevant functional mobility improvements were demonstrated with pegzilarginase treatment. These effects were sustained long-term through additional 24 weeks of subsequent exposure. Pegzilarginase was well-tolerated, with adverse events being mostly transient and mild/moderate in severity. Interpretation: These results support pegzilarginase as the first potential treatment to normalize pArg in ARG1-D and achieve clinically meaningful improvements in functional mobility. Funding: Aeglea BioTherapeutics.

Induced pluripotent stem cell technology as diagnostic tool in patients with suspected ornithine transcarbamylase deficiency lacking genetic confirmation.

Ornithine transcarbamylase (OTC) deficiency (OTCD) is an X-linked urea cycle disorder. In females - undergoing random X chromosomal inactivation (XCI) - disease severity depends on the XCI pattern. Hence, female OTCD subjects with favorable XCI display normal OTC expression and activity and are healthy carriers. Whereas females undergoing less favorable XCI may suffer from severe and fatal OTCD. In approximately 20% of patients with biochemical evidence of OTCD, no mutation can be identified hampering definitive diagnosis and adequate treatment.Here, we describe a female patient with high suspicion of OTCD in whom molecular genetic work-up did not reveal pathogenic variants in the OTC gene. In her case, this was particularly challenging, since she was awaiting liver transplantation due to metabolic instability. In order to substantiate the suspected diagnosis of OTCD, we applied our previously reported in vitro OTCD liver disease model. Patient-derived skin fibroblasts were reprogrammed into human induced pluripotent stem cells (hiPSCs) followed by differentiation into hepatocytes (hiPSC-Heps). Among five randomly selected hiPSC clones - differentiated into hiPSC-Heps - one clone expressed OTC protein, while the four remaining clones lacked OTC expression, supporting the patient's suspected diagnosis of OTCD.To conclude, we demonstrate that hiPSC technology is a powerful diagnostic tool to substantiate the suspected diagnosis of OTCD in patients lacking genetic confirmation. Furthermore, selecting clones that exclusively express the wild-type OTC protein, could be used strategically as cellular therapy in future. Ultimately, this approach might be applicable to virtually any X-linked disease. Synopsis: Induced pluripotent stem cell technology is a powerful diagnostic tool to substantiate the suspected diagnosis of OTCD in patients lacking genetic confirmation.

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

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

Treatment and management for children with urea cycle disorder in chronic stage. / å°¿ç´ å¾ªçŽ¯éšœç¢æ‚£å„¿æ ¢æ€§æœŸæ²»ç–—å’Œç®¡ç†.

Urea cycle disorder (UCD) is a group of inherited metabolic diseases with high disability or fatality rate, which need long-term drug treatment and diet management. Except those with Citrin deficiency or liver transplantation, all pediatric patients require lifelong low protein diet with safe levels of protein intake and adequate energy and lipids supply for their corresponding age; supplementing essential amino acids and protein-free milk are also needed if necessary. The drugs for long-term use include nitrogen scavengers (sodium benzoate, sodium phenylbutyrate, glycerol phenylbutyrate), urea cycle activation/substrate supplementation agents (N-carbamylglutamate, arginine, citrulline), etc. Liver transplantation is recommended for pediatric patients not responding to standard diet and drug treatment, and those with severe progressive liver disease and/or recurrent metabolic decompensations. Gene therapy, stem cell therapy, enzyme therapy and other novel technologies may offer options for treatment in UCD patients. The regular biochemical assessments like blood ammonia, liver function and plasma amino acid profile are needed, and physical growth, intellectual development, nutritional intake should be also evaluated for adjusting treatment in time.

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.

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

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

Coma With Hyperammonemia in a Patient With Kwashiorkor.

We describe a case of coma-related hyperammonemia in a woman presenting with severe edematous malnutrition (Kwashiorkor-like), without underlying hepatic disease. Our main hypothesis is that the patient developed a functional urea cycle disorder, due to the inability to synthesize N-acetylglutamate which is the activator of the first enzymes (carbamoyl phosphate synthetase) of urea cycle, in a context of severe deficiency of essential amino acids and of acetyl-CoA. Severe hyperammonemia is a medical emergency exposing to the risk of cerebral edema. Urgent treatment should interrupt protein intake, stimulate protein anabolism, and remove ammonia from the blood using renal replacement therapy and ammonia scavengers. Hyperammonemia should be searched in case of unexplained coma, even among patients without hepatic disorder, in particular among young patients. Hyperammonemia should also be searched among patients with severe protein-calorie malnutrition.

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

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

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

OBJECTIVES: Carbamoyl phosphate synthetase 1 (CPS1) deficiency is a severe urea cycle disorder. Patients can present with hyperammonemic coma in the first days of life. Treatment includes nitrogen scavengers, reduced protein intake and supplementation with L-arginine and/or L-citrulline. N-carbamoyl glutamate (NCG) has been hypothesized to stimulate the residual CPS1 function, although only few patients are reported. CASE PRESENTATION: We report a patient with neonatal-onset CPS1 deficiency who received NCG in association with nitrogen scavenger and L-citrulline. The patient carried the novel variants CPS1-c.2447A>G p.(Gln816Arg) and CPS1-c.4489T>C p.(Tyr1497His). The latter is localized in the C-terminal allosteric domain of the protein, and is implicated in the binding of the natural activator N-acetyl-L-glutamate. NCG therapy was effective in controlling ammonia levels, allowing to increase the protein intake. CONCLUSIONS: Our data show that the response to NCG can be indicated based on the protein structure. We hypothesize that variants in the C-terminal domain may be responsive to NCG therapy.

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

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

Clinical and genetic analysis of a case of late onset carbamoyl phosphate synthase I deficiency caused by CPS1 mutation and literature review.

BACKGROUND: Carbamoyl phosphate synthetase I defect (CPS1D) is a rare disease with clinical case reports mainly in early neonates or adults, with few reports of first onset in late neonatal to childhood. We studied the clinical and genotypic characteristics of children with childhood onset CPS1D caused by two loci mutations (one of these is a rarely reported non-frame shift mutation) in the CPS1. CASE PRESENTATION: We present a rare case of adolescent-onset CPS1D that had been misdiagnosed due to atypical clinical features, and further investigations revealed severe hyperammonemia (287µmol/L; reference range 11.2 ~ 48.2umol/L). MRI of the brain showed diffuse white matter lesions. Blood genetic metabolic screening showed elevated blood alanine (757.06umol/L; reference range 148.8 ~ 739.74umol/L) and decreased blood citrulline (4.26umol/L; reference range 5.45 ~ 36.77umol/L). Urine metabolic screening showed normal whey acids and uracil. Whole-exome sequencing revealed compound heterozygous mutations in the CPS1, a missense mutation (c.1145 C > T) and an unreported de novo non-frame shift mutation (c.4080_c.4091delAGGCATCCTGAT), respectively, which provided a clinical diagnosis. CONCLUSION: A comprehensive description of the clinical and genetic features of this patient, who has a rare age of onset and a relatively atypical clinical presentation, will facilitate the early diagnosis and management of this type of late onset CPS1D and reduce misdiagnosis, thus helping to reduce mortality and improve prognosis. It also provides a preliminary understanding of the relationship between genotype and phenotype, based on a summary of previous studies, which reminds us that it may help to explore the pathogenesis of the disease and contribute to genetic counselling and prenatal diagnosis.

Barriers to a successful healthcare transition for individuals with urea cycle disorders.

The pediatric to adult healthcare transition (HCT) is a process for individuals with chronic health conditions to gradually shift from a pediatric to an adult-oriented care system. Autonomy and self-management skills required for an individual's HCT readiness can be evaluated through the transition readiness assessment questionnaire (TRAQ). Despite general HCT preparation guidelines, little is known about the HCT experience of individuals with a urea cycle disorder (UCD). This is the first study to report the parent or guardian perception of the HCT process in children with a UCD by investigating the stages of transition readiness and transition outcome. We identify barriers to HCT readiness and planning, along with deficiencies in transition outcome for individuals with a UCD. For children that received special education services compared to those that did not, significantly lower transition readiness scores were identified in the total TRAQ score (p = 0.03) and in the domains of tracking health issues (p = 0.02), talking with providers (p = 0.03), and managing daily activities (p = 0.01). There was a lack of HCT preparation as most subjects did not have a HCT discussion with their healthcare provider before age 26. Deficiencies in HCT outcome are demonstrated by individuals with a UCD reporting delays in needed medical care and dissatisfaction with their healthcare services. Considerations for facilitating a successful HCT for individuals with a UCD include providing individualized education, appointing a transition coordinator, allowing flexibility in HCT timing, and ensuring that the individual recognizes concerning UCD symptoms and knows when to seek medical care.

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

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

Arginase 1 Deficiency in Patients Initially Diagnosed with Hereditary Spastic Paraplegia.

Background: Arginase 1 Deficiency (ARG1-D) is a rare autosomal recessive urea cycle disorder (UCD) characterized by pathologic elevation of plasma arginine and debilitating manifestations. Based on clinical commonalities and low disease awareness, ARG1-D can be diagnosed as hereditary spastic paraplegia (HSP), leading to treatment delays. Cases: A Hispanic woman with unremarkable medical history experienced progressive lower-limb spasticity in her 20s and received a diagnosis of HSP. She developed significant gait abnormalities and is unable to walk without assistance. More recently, two Hispanic brothers with childhood-onset manifestations including lower-limb spasticity, developmental delays, and seizures presented with suspected HSP. All three patients were ultimately diagnosed with ARG1-D based on plasma arginine several-fold above normal levels and loss-of-function ARG1 variants. Disease progression occurred before ARG1-D was correctly diagnosed. Literature Review: Retrospective analyses demonstrate that diagnostic delays in ARG1-D are common and can be lengthy. Because of clinical similarities between ARG1-D and HSP, such as insidious onset and progressive spasticity, accurate diagnosis of ARG1-D is challenging. Timely ARG1-D diagnosis is critical because this UCD is a treatable genetic cause of progressive lower-limb spasticity. Conclusions: Arginase 1 Deficiency should be considered in HSP differential diagnosis until biochemically/genetically excluded, and should be routinely included in HSP gene panels.