Neonatal-onset CPSI deficiency is the most common form of the disease. Prenatal period and birth are usually uneventful, and affected neonates may develop normally during the first few days of life. Most commonly, parents present their children aged less than a week, claiming feeding difficulties and vomiting. Additionally, the child may be noted to suffer from intermittent hypothermia; hyperventilation and hypotonia may be observed. These symptoms result from an accumulation of neurotoxic ammonia and consequent hyperammonemic encephalopathy. Thus, they are frequently accompanied by reduced consciousness, which may range from lethargy and somnolence to coma, and seizures. Although these symptoms are not specific for CPSI deficiency, they should prompt a strong suspicion of UCD.

Less commonly, symptom onset occurs in patients who experienced an unremarkable postnatal period. Complaints reported by individuals suffering from late-onset CPSI deficiency generally comprise chronic headaches, nausea, and vomiting. Similar to neonates suffering from hyperammonemia, elder patients may experience seizures and present with a reduced level of consciousness. Their mental state may be altered, and motor functions may be compromised [10]. Symptoms typically exacerbate during hyperammonemic crises, and those may be triggered by protein overload, fasting, infectious diseases or other stressors that stimulate protein catabolism. Non-compliance with therapeutic regimens may also lead to an acute aggravation of symptoms.

• Developmental Delay

  An autosomal recessive disorder (OMIM:237300) of the urea cycle, which is chemically characterised by hyperammonaemia and clinically characterised by protein intolerance, intermittent ataxia, seizures, lethargy, developmental delay and mental retardation [medical-dictionary.thefreedictionary.com]

  Analyzes chromosomes in newborns and infants for changes that can explain certain birth defects or developmental delays. Multiple testing options providing information on the genetic health of your baby during the first and second trimesters. [integratedgenetics.com]

  Clinical features include protein intolerance, intermittent ataxia, seizures, lethargy, developmental delay and mental retardation. [uniprot.org]

  […] transporter SLC7A7 (14q11.2)* Biochemical profile: Elevated urine lysine, ornithine, and arginine Clinical features: Protein intolerance, episodic hyperammonemia, growth and developmental delay, diarrhea, vomiting, hepatomegaly, cirrhosis, leucopenia [msdmanuals.com]

  Complications of carbamoyl phosphate synthetase I deficiency may include developmental delay and mental retardation. [en.wikipedia.org]

• Hypothermia

  The classic symptoms appear between 24hrs and 48hrs after birth (but not prior to 24hrs) and include convulsions, hyperventilation, ataxia, hypothermia, lethargy, vomiting and poor feeding. [themedicalbiochemistrypage.org]

  Severe hyperammonemia continues and manifests with postprandial vomiting, hypothermia, hypotonia, seizures, coma, and can lead to death. Outside the newborn period, patients can present at any time in life. [orpha.net]

  Additionally, they may note hypothermia, hyperventilation, and a decreased muscle tone. Children may become lethargic, somnolent and fall into coma. Seizures are common. [symptoma.com]

  Abstract A male infant, who appeared normal at birth, manifested hypothermia, irritability, and hypertonia 24 hours after beginning protein feedings. Increasing rigidity and coma ensued, and the child died at 75 hours of age. [nejm.org]

• Poor Feeding

  The classic symptoms appear between 24hrs and 48hrs after birth (but not prior to 24hrs) and include convulsions, hyperventilation, ataxia, hypothermia, lethargy, vomiting and poor feeding. [themedicalbiochemistrypage.org]

  The clinical manifestations are variable but common features include vomiting, hyperactivity or lethargy, diarrhoea, poor feeding, seizures, hypotonia, delayed psychomotor development and respiratory distress. [orpha.net]

  Poor feeding, low activity, and tachypnoea were observed, with rapid progression on day 2 after birth. [journals.lww.com]

  Symptoms include poor feeding, vomiting, lack of energy, low body temperature and weak muscle tone. These usually occur in the first few days of life. [rarediseases.info.nih.gov]

  The major presenting symptoms are vomiting, lethargy, hypothermia, and poor feeding. The estimated incidence of ASL deficiency is 1:70,000 newborns 5. [centogene.com]

• Weakness

  Symptoms include poor feeding, vomiting, lack of energy, low body temperature and weak muscle tone. These usually occur in the first few days of life. [rarediseases.info.nih.gov]

  PD patients exhibit a weak immune system and markedly elevated vulnerability to infections in general, and particularly those of the respiratory system, leading some who suffer from PD to acquire recurrent lung disease. [en.wikipedia.org]

  […] glycogen degradation in lysosomes small amount degraded in lysosomes by α-1,4-glucosidase via citrate shuttle transports acetyl-CoA from mito to cytoplasm via carnitine shuttle transports acyl-CoA from cytoplasm to mito toxic accumulation in cytosol weakness [quizlet.com]

  Two weaknesses you most need to work on improving in the next few years. We often disagree, writing I have to admire your consistency and commitment to Writing and to Robertson. [ofulijoj.cba.pl]

• Fatigue

  雑誌 Arch Biochem Biophys 536:101-8 (2013) DOI: 10.1016/j.abb.2013.04.009 文献 PMID: 20138956 著者 Wilkinson DJ, Smeeton NJ, Watt PW タイトル Ammonia metabolism, the brain and fatigue; revisiting the link. [genome.jp]

  Påvisning af choline i hjernescanninger anvendes derfor som indikation på neuroinflammation (1),Andre undersøgelser har vist, at inflammation i ACC udløser cytokininduceret fatigue og ... 2019-04-17 09:38 ME versus Sepsis Research in myalgic encephalomyelitis [blogglistene.no]

  Strategically located in the flow stream to collect a representative sample of wear debris circulating in the system: for example, engine swarf, bearing flakes, and fatigue chunks. [ofulijoj.cba.pl]

• Vomiting

  Location) Comments Ornithine-transcarbamoylase (OTC) deficiency (311250) OTC OTC (Xp21.1)* Biochemical profile: Elevated ornithine and glutamine, decreased citrulline and arginine, markedly increased urine orotate Clinical features: In males, recurrent vomiting [msdmanuals.com]

  This form of CPSID is initially characterized by refusal to eat, lethargy, lack of appetite, vomiting, and irritability. [rarediseases.org]

• Nausea

  Complaints reported by individuals suffering from late-onset CPSI deficiency generally comprise chronic headaches, nausea, and vomiting. [symptoma.com]

  Side effects of IV Ammonul® may occur in children, including nausea and vomiting. This may be controlled with antiemetic medications such as ondansetron, either prior to or during the infusion. [newenglandconsortium.org]

• Lactose Intolerance

  intolerance Congenital sucrase-isomaltase deficiency with starch intolerance Congenital sucrase-isomaltase deficiency without starch intolerance Congenital sucrase-isomaltase deficiency without sucrose intolerance Constitutional megaloblastic anemia [se-atlas.de]

• Jaundice

  […] relatively mild, AR sx: galactose in blood and urine, infantile cataracts may present as failure to track objects or develop a social smile absence of galactose-1-phosphate uridyltransferase AR accumulation of toxic substances sx: failure to thrive, jaundice [quizlet.com]

  She was unconscious, with moderate jaundice. Lung auscultation revealed coarse rales. Obvious hypotonia was observed, and the patient's primitive reflexes were absent. Bloody fluids from the gastric tube were found after admission. [journals.lww.com]

• Liver Dysfunction

  […] syndrome Multiple mitochondrial dysfunctions syndrome type 1 Multiple mitochondrial dysfunctions syndrome type 2 Multiple mitochondrial dysfunctions syndrome type 3 Multiple osteochondromas Multiple sulfatase deficiency Muscle-eye-brain disease NARP [se-atlas.de]

• Arthritis

  Association of HLA-DRB1 haplotypes with rheumatoid arthritis severity, mortality, and treatment response. JAMA. doi:10.1001/jama.2015.3435. More information [docplayer.net]

  It can be triggered by repetitive motion, arthritis, pregnancy, stroke. Some recent research indicates that the foods you eat may play a role in your susceptibility. [catsclem.nl]

• Seizure

  Manifestations include hyperammonemia with irritability, lethargy, headache, seizures, confusion, avoidance of high-protein meals, axial hypotonia and cognitive disability. [orpha.net]

  Within 24 hours, the patient developed generalized tonic-clonic seizures and was transferred to a tertiary care hospital. Hyperammonemia (1000 µmol/L; normal, FULL TEXT [annals.org]

  Abstract Shortly after birth, a newborn girl developed anorexia, hypotonia, apneic attacks and seizures. After 61 h the child died in coma. [ncbi.nlm.nih.gov]

  Elevated ornithine and glutamine, decreased citrulline and arginine, markedly increased urine orotate Clinical features: In males, recurrent vomiting, irritability, lethargy, hyperammonemic coma, cerebral edema, spasticity, intellectual disability, seizures [msdmanuals.com]

• Lethargy

  Clinical description In the neonatal-onset form of CPS1D, patients are usually healthy at birth but after few days they begin to manifest with lethargy and unwillingness to feed. [orpha.net]

  An autosomal recessive disorder (OMIM:237300) of the urea cycle, which is chemically characterised by hyperammonaemia and clinically characterised by protein intolerance, intermittent ataxia, seizures, lethargy, developmental delay and mental retardation [medical-dictionary.thefreedictionary.com]

  Definition : A urea cycle disorder manifesting in infancy as lethargy, emesis, seizures, alterations of muscle tone, abnormal eye movements, and an elevation of serum ammonia. [sideeffects.embl.de]

  This form of CPSID is initially characterized by refusal to eat, lethargy, lack of appetite, vomiting, and irritability. [rarediseases.org]

• Ataxia

  An autosomal recessive disorder (OMIM:237300) of the urea cycle, which is chemically characterised by hyperammonaemia and clinically characterised by protein intolerance, intermittent ataxia, seizures, lethargy, developmental delay and mental retardation [medical-dictionary.thefreedictionary.com]

  Clinical features include protein intolerance, intermittent ataxia, seizures, lethargy, developmental delay and mental retardation. [uniprot.org]

  She later developed ataxia and truncal dystonia. [neurology.org]

  […] due to ubiquinone deficiency Autosomal recessive cerebellar ataxia-pyramidal signs-nystagmus-oculomotor apraxia syndrome Autosomal recessive congenital cerebellar ataxia due to GRID2 deficiency Autosomal recessive congenital cerebellar ataxia due to [se-atlas.de]

  The classic symptoms appear between 24hrs and 48hrs after birth (but not prior to 24hrs) and include convulsions, hyperventilation, ataxia, hypothermia, lethargy, vomiting and poor feeding. [themedicalbiochemistrypage.org]

• Irritability

  Comments Ornithine-transcarbamoylase (OTC) deficiency (311250) OTC OTC (Xp21.1)* Biochemical profile: Elevated ornithine and glutamine, decreased citrulline and arginine, markedly increased urine orotate Clinical features: In males, recurrent vomiting, irritability [msdmanuals.com]

  Manifestations include hyperammonemia with irritability, lethargy, headache, seizures, confusion, avoidance of high-protein meals, axial hypotonia and cognitive disability. [orpha.net]

  Neonatal onset results in clinical features that include irritability, vomiting, lethargy, seizures, neonatal hypotonia; respiratory alkalosis; hyperammonemia; coma, and death. [icd9data.com]

  The baby becomes irritable, then lethargic, and, if untreated, comatose. Without rapid recognition and aggressive treatment, the infant suffers devastating CNS damage, coma, and death. [emedicine.medscape.com]

  Irritable 0000737 Lethargy 0001254 Low plasma citrulline 0003572 Protein avoidance 0002038 Respiratory alkalosis 0001950 Vomiting Throwing up 0002013 Showing of 21 | Last updated: 7/1/2019 Making a diagnosis for a genetic or rare disease can often be [rarediseases.info.nih.gov]

• Encephalopathy

  Patients presenting with hyperammonemic encephalopathy require urgent medical attention to prevent permanent brain damage. [symptoma.com]

  Initial laboratory findings will include respiratory alkalosis which is the earliest objective indication of encephalopathy. The encephalopathy will progress to the point where mechanical ventilation is required. [themedicalbiochemistrypage.org]

  […] glutamine in OTCD patients with hyperammonemic encephalopathy. [ajnr.org]

  Ehlers-Danlos syndrome, musculocontractural type Encephalopathy due to GLUT1 deficiency Encephalopathy due to hydroxykynureninuria Encephalopathy due to prosaposin deficiency Encephalopathy due to sulfite oxidase deficiency Encephalopathy-hypertrophic [se-atlas.de]

  Unless promptly treated, it can result in encephalopathy, coma and death, or intellectual disability in surviving patients. Over recent decades, therapies for CPS1D have barely improved leaving the management of these patients largely unchanged. [bioportfolio.com]

Because there is a direct correlation between the severity of hyperammonemia, the duration of hyperammonemic coma and permanent brain damage [11], it is important to recognize symptoms of hyperammonemic encephalopathy and to identify the cause of neurological deterioration. In this context, serum ammonia levels should be determined in every patient suspicious of UCD or sepsis. In healthy individuals, blood concentrations of ammonia are maintained between 10 and 40 μmol/l [6]. Blood samples should also be analyzed with regards to glucose levels, concentrations of amino acids and acylcarnitines as well as hepatic and renal parameters. Hyperammonemia is the clinical hallmark of CPSI deficiency and other UCD, but the former entity is also associated with increased levels of glutamine and alanine and low concentrations of citrulline and arginine. Urine samples should be tested for excess excretion of orotic acid, and in a case of CPSI deficiency, the corresponding tests typically yield negative results. This diagnostic measure is of importance to distinguish CPSI deficiency from other, distal UCD. Eventually, molecular biological techniques may be employed to prove sequence anomalies within the gene encoding for CPSI.

Of note, magnetic resonance imaging of the brain is not required to confirm a tentative diagnosis of CPSI deficiency. It may be of prognostic value, though. Typical findings include cortical atrophy, basal ganglia lesions and white matter damage.

• Hyperammonemia

  Carbamoyl phosphate synthetase I deficiency is an inherited disorder that causes ammonia to accumulate in the blood (hyperammonemia). Ammonia, which is formed when proteins are broken down in the body, is toxic if the levels become too high. [ghr.nlm.nih.gov]

  Hyperammonemia, type III Hyperornithinemia hyperammonemia homocitrullinemia Hyperornithinemia hyperammonemia homocitrullinemia syndrome Hyperornithinemia-hyperammonemia-homocitrullinuria syndrome N-acetylglutamate synthetase deficiency Ornithine carbamoyltransferase [icd9data.com]

  If left untreated the hyperammonemia with result in coma and death. The severe effects of hyperammonemia are described in the Nitrogen Metabolism page. [themedicalbiochemistrypage.org]

  Further examination indicated severe hyperammonemia (serum ammonia level >500 μmol/L). [journals.lww.com]

  Minor shares of patients may benefit from the administration of N-carbamoyl glutamate, a compound generally prescribed to individuals diagnosed with hyperammonemia type 3. [symptoma.com]

• Hypoglycemia

  Metabolic acidosis and hypoglycemia impair tissue function, especially in the central nervous system. [en.wikipedia.org]

  hyperinsulinism, asymptomatic hyperammonemia Treatment: Prevention of hypoglycemia *Gene has been identified, and molecular basis has been elucidated. [msdmanuals.com]

  […] small amount degraded in lysosomes by α-1,4-glucosidase via citrate shuttle transports acetyl-CoA from mito to cytoplasm via carnitine shuttle transports acyl-CoA from cytoplasm to mito toxic accumulation in cytosol weakness, hypotonia, hypoketotic hypoglycemia [quizlet.com]

  Hypoglycemia (blood glucose of 2.01 mmol/L), hypernatremia (Na + of 153.8 mmol/L) and hyperchloremia (Cl − of 114.2 mmol/L) suggested a potential disturbance in homeostasis. [journals.lww.com]

  Please note that as the patient’s condition improves and anabolic homeostasis is restored, it may be necessary to rapidly eliminate or reduce the rate of the insulin infusion as hypoglycemia may develop. [newenglandconsortium.org]

• Hyperglycemia

  High IV dextrose solutions should not be decreased or stopped in the face of hyperglycemia. The goal is to keep the level from rising above 150 mg/dl. [newenglandconsortium.org]

• Ammonia Increased

  They may rapidly progress to respiratory alkalosis as ammonia increases with cerebral edema, seizures, loss of reflexes, hypothermia, apnea, and coma. [clinicaladvisor.com]

Causative treatment is not available. Affected individuals are recommended to adhere to a diet low in protein but should avoid fasting and insufficient supply of nutrients. In this context, it may be necessary to supplement essential amino acids, arginine and citrulline. Minor shares of patients may benefit from the administration of N-carbamoyl glutamate, a compound generally prescribed to individuals diagnosed with hyperammonemia type 3 [12]. N-carbamoyl glutamate serves as an allosteric activator of CPSI and thus complements N-acetyl glutamate provided by NAGS.

Patients presenting with hyperammonemic encephalopathy require urgent medical attention to prevent permanent brain damage. In order to decrease ammonia production and to revert the catabolic state of the patient, protein intake should be stopped completely for up to 48 hours and affected individuals should receive glucose infusions. Additional measures should be undertaken depending on the severity of hyperammonemia [13]:

• Supplementation of L-arginine and L-citrulline is indicated in neonatal and adult patients presenting with serum ammonia levels of more than 150 and 100 μmol/l, respectively.
• These patients should also receive ammonia scavengers, e.g., sodium benzoate, sodium phenylacetate, or sodium phenylbutyrate.
• Ammonia levels of more than 250 μmol/l may require hemodialysis or hemofiltration and this same therapy should be initiated immediately in patients presenting with ammonia concentrations of more than 500 μmol/l.

Liver transplantation may be an option for patients repeatedly suffering from hyperammonemic crises.

Unrecognized and untreated CPSI deficiency is generally fatal, and this particularly applies to the more severe, neonatal-onset form of the disease. Even if medical care is ensured, about one-fourth of neonates carrying CPSI gene defects succumb to the disease. According to a retrospective study conducted in Japan, late-onset CPSI deficiency is not associated with significant mortality [9]. Nevertheless, hyperammonemic crises may induce irreversible brain damage and result in mental retardation and disability of survivors. Any diagnostic or therapeutic delay increases the likelihood of a poor neurological outcome.

CPSI deficiency is caused by mutations in the gene encoding for CPSI. This gene is located on the short arm of chromosome 2 and is physiologically expressed by hepatocytes and epithelial cells of the intestinal mucosa [2]. It spans more than 120 kb corresponding to a total of 38 exons and 37 introns that are subsequently translated into a 1,500-amino-acid protein [3]. To date, more than 200 mutations of the CPSI gene have been described, and they may result in an absent or reduced activity of the enzyme [2] [4]. Indeed, the level of residual enzymatic activity has been related to the delay of symptom onset, i.e., absent CPSI activity is associated with neonatal-onset disease while partial enzymatic activity is detectable in those individuals presenting with late-onset CPSI deficiency. The majority of gene defects related to CPSI deficiency are missense mutations, which are most likely to provoke an incomplete functional impairment of the enzyme [4]. Insertion, deletion, and duplication of sequence segments have also been detected. All forms of CPSI deficiency known to date are inherited as an autosomal recessive trait.

In the United States, the annual incidence of CPSI deficiency has been calculated to be 1 in 300,000 live births [5]. Based on estimates of an overall incidence of UCD of 1 in 35,000 neonates, CPSI deficiency accounts for about one in nine cases of UCD. Neither racial nor gender predilection have been reported to date. Most commonly, CPSI deficiency is diagnosed in neonates. Otherwise, symptom onset may occur at any age and indeed, case reports on hyperammonemic encephalopathy due to previously undiagnosed CPSI deficiency in adults aged 40 years and older are available [6].

In the human body, ammonia mainly arises from the conversion of glutamate to α-ketoglutarate, and the hepatic urea cycle is the single most important pathway of ammonia detoxification. Incorporation of ammonia into the urea cycle requires bicarbonate and active CPSI; subsequent steps of the urea cycle cannot take place if CPSI does not supply carbamoyl phosphate. Consequently, CPSI deficiency is associated with an accumulation of ammonia. Excess ammonia is distributed throughout the whole body and is able to cross the blood-brain barrier. Here, it provokes cytotoxic and possibly vasogenic brain edema, which may manifest in form of seizures, tremor, asterixis, delirium and a reduced level of awareness [7]. Increases in intracranial pressure may be detrimental and cause hyperammonemic coma and death, but even less severe hyperammonemic crises may provoke irreversible neuronal loss.

To a lesser extent, CPSI is expressed by epithelial cells lining the intestinal tract. Similar to its function in hepatocytes, the intestinal enzyme catalyzes the formation of carbamoyl phosphate, which is subsequently converted to citrulline. Citrulline, in turn, is utilized for the synthesis of arginine, a semi-essential amino acid. Thus, patients suffering from CPSI deficiency present with low serum levels of citrulline and arginine. Little is known about the clinical consequences of those amino acid deficiencies although it has been suggested that endothelial function and cytokine release by immune cells may be altered [8].

Families affected by CPSI deficiency should be offered genetic counseling and prenatal screenings. Fetal DNA may be extracted from chorionic villus or amniotic fluid samples and may be examined accordingly [12].

Although analyses of serum ammonia levels in few-days-old neonates may allow for the detection of UCD before hyperammonemic encephalopathy occurs, they are not yet routinely carried out.

Carbamoyl phosphate synthetase deficiency is a proximal urea cycle disorder (UCD) that may also be referred to as carbamoyl phosphate synthetase I (CPSI) deficiency or hyperammonemia type 1. The former designation specifies the disease to result from the reduced activity of the mitochondrial enzyme CPSI. Of note, carbamoyl phosphate synthetase II (CPSII) is a cytosolic enzyme that catalyzes the conversion of glutamine, bicarbonate, and ATP to glutamate, ADP, phosphate, and carbamoyl phosphate. CPSII plays a crucial role in pyrimidine biosynthesis but is not involved in ammonia detoxification.

CPSI, in turn, is required for the synthesis of carbamoyl phosphate from ammonia and bicarbonate, and this reaction is the rate-limiting step of the urea cycle [1]. Consequently, CPSI deficiency is associated with an accumulation of neurotoxic ammonia. CPSI deficiency is a hereditary disorder and thus, affected individuals often develop severe hyperammonemia within few days after birth. Indeed, neonatal-onset CPSI deficiency is the most common form of the disease. Nevertheless, symptom onset may be delayed until years after birth and even until well into adulthood. Late onset of symptoms may be related to a greater residual activity of the enzyme.

Of note, CPSI depends on the supply of N-acetyl-glutamate, which acts as an allosteric activator of the former. N-acetyl glutamate is provided by N-acetyl glutamate synthase (NAGS), an enzyme that catalyzes the conversion of glutamate and acetyl-CoA to N-acetyl glutamate. Hyperammonemia type 3 is a pathogenetically different but clinically similar UCD provoked by NAGS deficiency.

Carbamoyl phosphate synthetase deficiency is a rare urea cycle disorder. It is caused by mutations in the gene encoding for carbamoyl phosphate synthetase I (CPSI), an enzyme required for ammonia detoxification.

Ammonia is a by-product arising during the breakdown of proteins, amino acids and other molecules containing nitrogen. CPSI catalyzes the conversion of ammonia and bicarbonate to carbamoyl phosphate, which is subsequently processed to urea. Several biochemical reactions take place in between, and this complex pathway is referred to as the urea cycle. It allows for the conversion of toxic ammonia into a nitrogen compound that can easily be excreted. In a case of CPSI deficiency, carbamoyl phosphate is not or is only insufficiently synthesized. Consequently, ammonia accumulates.

The central nervous system is most sensitive to increased levels of ammonia and patients suffering from CPSI deficiency thus present with hyperammonemic encephalopathy. Due to the disease being caused by a gene defect, symptom onset generally occurs early in life. In fact, parents of healthy born neonates may note feeding difficulties and vomiting after the first few days of life of their child. Additionally, they may note hypothermia, hyperventilation, and a decreased muscle tone. Children may become lethargic, somnolent and fall into coma. Seizures are common. Less frequently, residual activity of CPSI delays symptom onset until later periods of life. Here, chronic headaches, an altered mental status, and motor dysfunction are characteristic of CPSI deficiency.

It is of utmost importance to recognize hyperammonemic crises and to initiate treatment as early as possible. This way, permanent brain damage, and death may possibly be avoided. In such cases, immediate measures are undertaken to lower serum concentrations of ammonia, but patients have to adhere to a life-long therapeutic regimen including a diet low in protein and amino acid supplementation. Unfortunately, causative treatment is not available and CPSI deficiency continues to be a life-threatening disease, particularly in neonates.

1. Martínez AI, Pérez-Arellano I, Pekkala S, Barcelona B, Cervera J. Genetic, structural and biochemical basis of carbamoyl phosphate synthetase 1 deficiency. Mol Genet Metab. 2010; 101(4):311-323.
2. Funghini S, Thusberg J, Spada M, et al. Carbamoyl phosphate synthetase 1 deficiency in Italy: clinical and genetic findings in a heterogeneous cohort. Gene. 2012; 493(2):228-234.
3. Summar ML, Hall LD, Eeds AM, et al. Characterization of genomic structure and polymorphisms in the human carbamyl phosphate synthetase I gene. Gene. 2003; 311:51-57.
4. Häberle J, Shchelochkov OA, Wang J, et al. Molecular defects in human carbamoy phosphate synthetase I: mutational spectrum, diagnostic and protein structure considerations. Hum Mutat. 2011; 32(6):579-589.
5. Summar ML, Koelker S, Freedenberg D, et al. The incidence of urea cycle disorders. Mol Genet Metab. 2013; 110(1-2):179-180.
6. Bates TR, Lewis BD, Burnett JR, et al. Late-onset carbamoyl phosphate synthetase 1 deficiency in an adult cured by liver transplantation. Liver Transpl. 2011; 17(12):1481-1484.
7. Scott TR, Kronsten VT, Hughes RD, Shawcross DL. Pathophysiology of cerebral oedema in acute liver failure. World J Gastroenterol. 2013;19(48):9240-9255.
8. Morris SM, Jr. Arginases and arginine deficiency syndromes. Curr Opin Clin Nutr Metab Care. 2012;15(1):64-70.
9. Nakamura K, Kido J, Mitsubuchi H, Endo F. Diagnosis and treatment of urea cycle disorder in Japan. Pediatr Int. 2014; 56(4):506-509.
10. Summar ML, Dobbelaere D, Brusilow S, Lee B. Diagnosis, symptoms, frequency and mortality of 260 patients with urea cycle disorders from a 21-year, multicentre study of acute hyperammonaemic episodes. Acta Paediatr. 2008;97(10):1420-1425.
11. Auron A, Brophy PD. Hyperammonemia in review: pathophysiology, diagnosis, and treatment. Pediatr Nephrol. 2012; 27(2):207-222.
12. Häberle J, Boddaert N, Burlina A, et al. Suggested guidelines for the diagnosis and management of urea cycle disorders. Orphanet J Rare Dis. 2012; 7:32.
13. Ah Mew N, McCarter R, Daikhin Y, et al. Augmenting ureagenesis in patients with partial carbamyl phosphate synthetase 1 deficiency with N-carbamyl-L-glutamate. J Pediatr. 2014; 165(2):401-403.e403.