Modulation of brain energy metabolism in hepatic encephalopathy: impact of glucose metabolic dysfunction.

Cerebral function is linked to a high level of metabolic activity and relies on glucose as its primary energy source. Glucose aids in the maintenance of physiological brain activities; as a result, a disruption in metabolism has a significant impact on brain function, launching a chain of events that leads to neuronal death. This metabolic insufficiency has been observed in a variety of brain diseases and neuroexcitotoxicity disorders, including hepatic encephalopathy. It is a significant neurological complication that develops in people with liver disease, ranging from asymptomatic abnormalities to coma. Hyperammonemia is the main neurotoxic villain in the development of hepatic encephalopathy and induces a wide range of complications in the brain. The neurotoxic effects of ammonia on brain function are thought to be mediated by impaired glucose metabolism. Accordingly, in this review, we provide an understanding of deranged brain energy metabolism, emphasizing the role of glucose metabolic dysfunction in the pathogenesis of hepatic encephalopathy. We also highlighted the differential metabolic profiles of brain cells and the status of metabolic cooperation between them. The major metabolic pathways that have been explored are glycolysis, glycogen metabolism, lactate metabolism, the pentose phosphate pathway, and the Krebs cycle. Furthermore, the lack of efficacy in current hepatic encephalopathy treatment methods highlights the need to investigate potential therapeutic targets for hepatic encephalopathy, with regulating deficient bioenergetics being a viable alternative in this case. This review also demonstrates the importance of the development of glucose metabolism-focused disease diagnostics and treatments, which are now being pursued for many ailments.

Seizure Characteristics and EEG Features in Intoxication Type and Energy Deficiency Neurometabolic Disorders in the Pediatric Intensive Care Unit: Single-Center Experience Over 10 Years.

BACKGROUND: Acute metabolic crises in inborn errors of metabolism (such as urea cycle disorders, organic acidemia, maple syrup urine disease, and mitochondrial disorders) are neurological emergencies requiring management in the pediatric intensive care unit (PICU). There is a paucity of data pertaining to electroencephalograms (EEG) characteristics in this cohort. We hypothesized that the incidence of background abnormalities and seizures in this cohort would be high. Neuromonitoring data from our center's PICU over 10 years are presented in this article. METHODS: Data were collected by retrospective chart review for patients with the aforementioned disorders who were admitted to the PICU at our institution because of metabolic/neurologic symptoms from 2008 to 2018. Descriptive statistics (χ2 test or Fisher's exact test) were used to study the association between EEG parameters and outcomes. RESULTS: Our cohort included 40 unique patients (8 with urea cycle disorder, 7 with organic acidemia, 3 with maple syrup urine disease, and 22 with mitochondrial disease) with 153 admissions. Presenting symptoms included altered mentation (36%), seizures (41%), focal weakness (5%), and emesis (28%). Continuous EEG was ordered in 34% (n = 52) of admissions. Twenty-three admissions were complicated by seizures, including eight manifesting as status epilepticus (seven nonconvulsive and one convulsive). Asymmetry and focal slowing on EEG were associated with seizures. Moderate background slowing or worse was noted in 75% of EEGs. Among those patients monitored on EEG, 4 (8%) died, 3 (6%) experienced a worsening of their Pediatric Cerebral Performance Category (PCPC) score as compared to admission, and 44 (86%) had no change (or improvement) in their PCPC score during admission. CONCLUSIONS: This study shows a high incidence of clinical and subclinical seizures during metabolic crisis in patients with inborn errors of metabolism. EEG background features were associated with risk of seizures as well as discharge outcomes. This is the largest study to date to investigate EEG features and risk of seizures in patients with neurometabolic disorders admitted to the PICU. These data may be used to inform neuromonitoring protocols to improve mortality and morbidity in inborn errors of metabolism.

Dual Dialysis for Post-bilateral Orthotopic Lung Transplantation Hyperammonemia.

Hyperammonemia is a metabolic disorder characterized by supraphysiologic ammonia (NH3) concentrations in the blood. Although usually seen in adults with liver disease, hyperammonemia is a notable complication in 4.1% of lung transplants. It is associated with cerebral edema and neurological dysfunction and carries up to 75% mortality in critically ill patients. Opportunistic infections caused by Mycoplasma and Ureaplasma species have been implicated as the cause of this metabolic disturbance. Literature in neonates has shown that renal replacement therapy (RRT) is the best choice for treating patients with neurologic manifestations of hyperammonemia, in cases of NH3 clearance than continuous renal replacement therapy (CRRT). In contrast, continuous venovenous hemodialysis (CVVHD) is usually better tolerated for patients with hemodynamic instability for NH3 clearance. NH3 is a small molecule whose clearance mirrors urea in dialysis. Even though RRT can be a treatment modality for hyperammonemia in adults and neonates, there is very little literature on adults. We present a unique case demonstrating improvement in neurologic manifestations of hyperammonemia by using both IHD and CVVHD in an adult patient.

A founder mutation in CA5A causing intrafamilial and interfamilial phenotypic variability in a cohort of 18 patients with carbonic anhydrase VA deficiency.

Carbonic anhydrase VA (CA-VA) deficiency is a rare cause of hyperammonemia caused by biallelic mutations in CA5A. Most patients present with hyperammonemic encephalopathy in early infancy to early childhood, and patients usually have no further recurrence of hyperammonemia with a favorable outcome. This retrospective cohort study reports 18 patients with CA-VA deficiency caused by homozygosity for a founder mutation, c.59G>A p.(Trp20*) in CA5A. The reported patients show significant intrafamilial and interfamilial variability, and display atypical clinical features. Two adult patients were asymptomatic, 7/18 patients had recurrent hyperammonemia, 7/18 patients developed variable degree of developmental delay, 9/11 patients had hyperCKemia, and 7/18 patients had failure to thrive. Microcephaly was seen in three patients and one patient developed a metabolic stroke. The same variant had been reported already in a single South Asian patient presenting with neonatal hyperammonemic encephalopathy and subsequent development of seizures and developmental delay. This report highlights the limitations of current understanding of the pathomechanisms involved in this disorder, and calls for further evaluation of the possible role of genetic modifiers in this condition.

Research progress in the pathogenesis of sepsis-associated encephalopathy.

Sepsis is a syndrome that causes dysfunction of multiple organs due to the host's uncontrolled response to infection and is a significant contributor to morbidity and mortality in intensive care units worldwide. Surviving patients are often left with acute brain injury and long-term cognitive impairment, known as sepsis-associated encephalopathy (SAE). In recent years, researchers have directed their focus towards the pathogenesis of SAE. However, due to the complexity of its development, there remains a lack of effective treatment measures that arise as a serious issue affecting the prognosis of sepsis patients. Further research on the possible causes of SAE aims to provide clinicians with potential therapeutic targets and help develop targeted prevention strategies. This paper aims to review recent research on the pathogenesis of SAE, in order to enhance our understanding of this syndrome.

Impaired Consciousness Due to Hyperammonemia During S-1 Administration for Unresectable Pancreatic Cancer.

A 71-year-old woman diagnosed with unresectable locally advanced pancreatic cancer was initially treated with gemcitabine and nab-paclitaxel as first-line therapy. The tumor exhibited no significant progression; however, after 12 cycles, the patient developed drug-induced interstitial pneumonia, leading to the discontinuation of gemcitabine and nab-paclitaxel therapy. Following recovery from pneumonia, S-1 therapy was initiated as second-line treatment. During S-1 treatment, she was hospitalized because of impaired consciousness and was subsequently diagnosed with hyperammonemia induced by S-1. Although rarely reported, S-1-induced hyperammonemia is potentially a significant adverse effect. Here, we herein report the case of a patient with pancreatic cancer.

The Effect of L-Carnitine on Critical Illnesses Such as Traumatic Brain Injury (TBI), Acute Kidney Injury (AKI), and Hyperammonemia (HA).

L-carnitine (LC) through diet is highly beneficial for critical patients. Studies have found that acetyl-L-carnitine (ALC) can reduce cerebral edema and neurological complications in TBI patients. It significantly improves their neurobehavioral and neurocognitive functions. ALC has also been shown to have a neuroprotective effect in cases of global and focal cerebral ischemia. Moreover, it is an effective agent in reducing nephrotoxicity by suppressing downstream mitochondrial fragmentation. LC can reduce the severity of renal ischemia-reperfusion injury, renal cast formation, tubular necrosis, iron accumulation in the tubular epithelium, CK activity, urea levels, Cr levels, and MDA levels and restore the function of enzymes such as SOD, catalase, and GPx. LC can also be administered to patients with hyperammonemia (HA), as it can suppress ammonia levels. It is important to note, however, that LC levels are dysregulated in various conditions such as aging, cirrhosis, cardiomyopathy, malnutrition, sepsis, endocrine disorders, diabetes, trauma, starvation, obesity, and medication interactions. There is limited research on the effects of LC supplementation in critical illnesses such as TBI, AKI, and HA. This scarcity of studies highlights the need for further research in this area.

A unique case of hyperammonemia due to CA5A deficiency: Impact of coexisting gene mutations, pseudogene, and microdeletion.

Carbonic anhydrase 5A (CA5A) belongs to a family of carbonic anhydrases which are zinc metalloenzymes involved in the reversible hydration of CO2 to bicarbonate. Mutations in CA5A are very rare and known to cause Carbonic anhydrase 5A deficiency (CA5AD), an autosomal recessive inborn error of metabolism characterized clinically by acute onset of encephalopathy in infancy or early childhood. CA5A also has two very identical pseudogenes whose interference may result in compromised accuracy in targeted sequencing. We report a unique case of CA5AD caused by compound heterozygous variant (NM_001739.2: c.721G>A: p.Glu241Lys & NM_001739.2: c.619-3420_c.774 + 502del4078bp) in an infant in order to expand the phenotypic spectrum and underscore the impact of pseudogenes, which can introduce complexities in molecular genetic analysis.

Hyperosmolarity in children with hyperammonemia: a risk of brain herniation at the start of renal replacement therapy.

Purpose: Renal replacement therapy (RRT) is used in hyperammonemia to reduce the concentration of ammonia in the blood. In the case of plasma hyperosmolarity, RRT can also rapidly decrease plasma osmolarity, which may increase cerebral edema in these patients and favor the occurrence of brain herniation. Methods: We conducted a retrospective clinical study in a tertiary care university-affiliated hospital. All patients admitted in a Pediatric Intensive Care Unit (PICU), less than 18 years old with ammonemia >150 µmol/L and who underwent RRT between January 2015 and June 2023 were included. We collected data on plasma osmolarity levels, osmolar gap and blood ammonia levels before and during RRT. Results: Eleven patients were included (10 with acute liver failure and 1 with a urea cycle disorders). Their mean age was 36.2 months. Before RRT, the median highest measured osmolarity was 320 (305-324) mOsm/L, whereas the median calculated osmolarity was 303 (293-314) mOsm/L, corresponding to an osmolar gap of 14 mOsm/L. Ammonia blood level over 400 µmol/L are significantly associated with higher plasma osmolarity (P-Value <0.001). In one case, a patient had a brain herniation episode after a quick osmolar drop. This episode was reversed by the administration of hyperosmolar agents and the temporary suspension of RRT. Conclusion: This study highlights the hyperosmolarity and high osmolar gap that occur in children with hyperammonemia. A careful monitoring and control of plasma osmolarity evolution may alert clinician on the risk of occurrence of neurological complication such as brain herniation.

Bedside assessment of sarcopenia in hospitalized patients with liver cirrhosis: Magnitude and clinical implications.

BACKGROUND: Sarcopenia is associated with many adverse outcomes in patients with cirrhosis. The tools currently in use for assessing sarcopenia have numerous flaws. We evaluated the utility of portable ultrasonography and a dynamometer for the bedside assessment of sarcopenia and its implications in hospitalized cirrhosis patients. METHODS: A dynamometer was used to test the hand-grip strength (HGS) and ultrasound was used to measure the thickness of the forearm and quadriceps muscles. HGS value < 27 kg for men and < 16 kg for women was taken as significant according to the European Working Group on Sarcopenia in Older People (EWGSOP2) criteria. The lower normal limit of muscle mass (5th percentile) was determined on 100 matched healthy controls. RESULTS: According to the EWGSOP2 criteria and HGS values, the prevalence of sarcopenia and probable sarcopenia among 300 cirrhosis patients were 56% and 62.3%, respectively. HGS alone identified sarcopenia in 88.9% of patients, while overestimated it in 6.3% of cases. The prevalence rate of sarcopenic obesity was 11%. Compared to patients without sarcopenia, sarcopenic patients had more complications of cirrhosis such as ascites, variceal bleeding, hepatic encephalopathy, spontaneous bacterial peritonitis, sepsis, hepatorenal syndrome and refractory ascites. In-hospital (p = 0.037), three-month (p < 0.001), and six-month (p < 0.001) mortality rates were all higher among sarcopenic patients. On cox regression survival analysis, overall six-month mortality was significantly higher in sarcopenic patients compared to patients without sarcopenia (hazard ratio, 6.37; 95% confidence interval, 3.15-12.8, p < 0.001). CONCLUSION: Bedside assessment of sarcopenia using a portable ultrasound machine and a dynamometer detects liver cirrhosis patients with high risk of complications and mortality.

Ammonia transporter RhBG initiates downstream signaling and functional responses by activating NFκB.

Transceptors, solute transporters that facilitate intracellular entry of molecules and also initiate intracellular signaling events, have been primarily studied in lower-order species. Ammonia, a cytotoxic endogenous metabolite, is converted to urea in hepatocytes for urinary excretion in mammals. During hyperammonemia, when hepatic metabolism is impaired, nonureagenic ammonia disposal occurs primarily in skeletal muscle. Increased ammonia uptake in skeletal muscle is mediated by a membrane-bound, 12 transmembrane domain solute transporter, Rhesus blood group-associated B glycoprotein (RhBG). We show that in addition to its transport function, RhBG interacts with myeloid differentiation primary response-88 (MyD88) to initiate an intracellular signaling cascade that culminates in activation of NFκB. We also show that ammonia-induced MyD88 signaling is independent of the canonical toll-like receptor-initiated mechanism of MyD88-dependent NFκB activation. In silico, in vitro, and in situ experiments show that the conserved cytosolic J-domain of the RhBG protein interacts with the Toll-interleukin-1 receptor (TIR) domain of MyD88. In skeletal muscle from human patients, human-induced pluripotent stem cell-derived myotubes, and myobundles show an interaction of RhBG-MyD88 during hyperammonemia. Using complementary experimental and multiomics analyses in murine myotubes and mice with muscle-specific RhBG or MyD88 deletion, we show that the RhBG-MyD88 interaction is essential for the activation of NFkB but not ammonia transport. Our studies show a paradigm of substrate-dependent regulation of transceptor function with the potential for modulation of cellular responses in mammalian systems by decoupling transport and signaling functions of transceptors.

Quo vadis ureagenesis disorders? A journey from 90 years ago into the future.

The pathway of ammonia disposal in the mammalian organism has been described in 1932 as a metabolic cycle present in the liver in different compartments. In 1958, the first human disorder affecting this pathway was described as a genetic condition leading to cognitive impairment and constant abnormalities of amino acid metabolism. Since then, defects in all enzymes and transporters of the urea cycle have been described, referring to them as primary urea cycle disorders causing primary hyperammonemia. In addition, there is a still increasing list of conditions that impact on the function of the urea cycle by various mechanisms, hereby leading to secondary hyperammonemia. Despite great advances in understanding the molecular background and the biochemical specificities of both primary and secondary hyperammonemias, there remain many open questions: we do not fully understand the pathophysiology in many of the conditions; we do not always understand the highly variable clinical course of affected patients; we clearly appreciate the need for novel and improved diagnostic and therapeutic approaches. This study does look back to the beginning of the urea cycle (hi)story, briefly describes the journey through past decades, hereby illustrating advancements and knowledge gaps, and gives examples for the extremely broad perspective imminent to some of the defects of ureagenesis and allied conditions.

Sialyltransferase ST3GAL6 silencing reduces α2,3-sialylated glycans to regulate autophagy by decreasing HSPB8-BAG3 in the brain with hepatic encephalopathy. / å”¾æ¶²é ¸ç³–åŸºè½¬ç§»é ¶ST3GAL6的沉默可通过减少α2,3-å”¾æ¶²é ¸åŒ–èšç³–é™ä½ŽHSPB8-BAG3è¡¨è¾¾ä»Žè€Œè°ƒæŽ§è‚æ€§è„‘ç— å°é¼ å¤§è„‘ä¸­çš„è‡ªå™¬.

End-stage liver diseases, such as cirrhosis and liver cancer caused by hepatitis B, are often combined with hepatic encephalopathy (HE); ammonia poisoning is posited as one of its main pathogenesis mechanisms. Ammonia is closely related to autophagy, but the molecular mechanism of ammonia's regulatory effect on autophagy in HE remains unclear. Sialylation is an essential form of glycosylation. In the nervous system, abnormal sialylation affects various physiological processes, such as neural development and synapse formation. ST3 ß|-galactoside α2,|3-sialyltransferase 6 (ST3GAL6) is one of the significant glycosyltransferases responsible for adding α2,3-linked sialic acid to substrates and generating glycan structures. We found that the expression of ST3GAL6 was upregulated in the brains of mice with HE and in astrocytes after ammonia induction, and the expression levels of α2,3-sialylated glycans and autophagy-related proteins microtubule-associated protein light chain 3 (LC3) and Beclin-1 were upregulated in ammonia-induced astrocytes. These findings suggest that ST3GAL6 is related to autophagy in HE. Therefore, we aimed to determine the regulatory relationship between ST3GAL6 and autophagy. We found that silencing ST3GAL6 and blocking or degrading α2,3-sialylated glycans by way of Maackia amurensis lectin-II (MAL-II) and neuraminidase can inhibit autophagy. In addition, silencing the expression of ST3GAL6 can downregulate the expression of heat shock protein ß8 (HSPB8) and Bcl2-associated athanogene 3 (BAG3). Notably, the overexpression of HSPB8 partially restored the reduced autophagy levels caused by silencing ST3GAL6 expression. Our results indicate that ST3GAL6 regulates autophagy through the HSPB8-BAG3 complex.

Host and fungal factors both contribute to cryptococcosis-associated hyperammonemia (cryptammonia).

Cryptococcus neoformans and Cryptococcus gattii are both known urease producers and have the potential to cause hyperammonemia. We hypothesized that the risk of hyperammonemia is increased by renal failure, burden of cryptococcal infection, and fungal strain characteristics. We performed a retrospective review of plasma ammonia levels in patients with cryptococcal infections. Risk factors for hyperammonemia were statistically compared between patients with and without hyperammonemia (>53 µmol/L). Cryptococcal cells from three patients included in the study were recovered from our biorepository. Strain characteristics including urease activity, ammonia production, growth curves, microscopy, melanin production, and M13 molecular typing were analyzed and compared with a wild-type (WT) C. neoformans strain. We included 29 patients, of whom 37.9% had hyperammonemia, 59% had disseminated cryptococcal infection (DCI), and 41% had isolated central nervous system infection. Thirty-eight percent of patients had renal failure and 28% had liver disease. Renal failure was associated with 4.4 times (95% confidence interval [CI] 1.5, 13.0) higher risk of hyperammonemia. This risk was higher in DCIs (RR 6.2, 95% CI 1.0, 40.2) versus isolated cryptococcal meningitis (RR 2.5, 95% CI, 0.40, 16.0). Liver disease and cryptococcal titers were not associated with hyperammonemia. C. neoformans from one patient with extreme hyperammonemia demonstrated a 4- to 5-fold increase in extracellular urease activity, slow growth, enlarged cell size phenotypes, and diminished virulence factors. Hyperammonemia was strongly associated with renal failure in individuals with DCI, surpassing associations with liver failure or cryptococcal titers. However, profound hyperammonemia in one patient was attributable to high levels of urease secretion unique to that cryptococcal strain. Prospective studies are crucial to exploring the significance of this association.IMPORTANCECryptococcus produces and secretes the urease enzyme to facilitate its colonization of the host. Urease breaks down urea into ammonia, overwhelming the liver's detoxification process and leading to hyperammonemia in some hosts. This underrecognized complication exacerbates organ dysfunction alongside the infection. Our study investigated this intricate relationship, uncovering a strong association between the development of hyperammonemia and renal failure in patients with cryptococcal infections, particularly those with disseminated infections. We also explore mechanisms underlying increased urease activity, specifically in strains associated with extreme hyperammonemia. Our discoveries provide a foundation for advancing research into cryptococcal metabolism and identifying therapeutic targets to enhance patient outcomes.

Hyperornithinemia-hyperammonemia-homocitrullinuria: a rare neurometabolic disorder in two siblings.

Hyperornithinemia-hyperammonemia-homocitrullinuria syndrome is an extremely rare disorder of urea cycle, with few patients reported worldwide. Despite hyperammonemia control, the long-term outcome remains poor with progressive neurological deterioration. We report the clinical, biochemical, and molecular features of two Lebanese siblings diagnosed with this disorder and followed for 8 and 15 years, respectively. Variable clinical manifestations and neurological outcome were observed. The patient with earlier onset of symptoms had a severe neurological deterioration while the other developed a milder form of the disease at an older age. Diagnosis was challenging in the absence of the complete biochemical triad and the non-specific clinical presentations. Whole exome sequencing revealed a homozygous variant, p.Phe188del, in the SLC25A15 gene, a French- Canadian founder mutation previously unreported in Arab patients. Hyperammonemia was controlled in both patients but hyperonithinemia persisted. Frequent hyperalaninemia spikes and lactic acidosis occured concomitantly with the onset of seizures in one of the siblings. Variable neurological deterioration and outcome were observed within the same family. This is the first report from the Arab population of the long-term outcome of this devastating neurometabolic disorder.

Cerebral Aspects of Portal Hypertension: Hepatic Encephalopathy.

Portal hypertension has cerebral consequences via its causes and complications, namely hepatic encephalopathy (HE), a common and devastating brain disturbance caused by liver insufficiency and portosystemic shunting. The pathogenesis involves hyperammonemia and systemic inflammation. Symptoms are disturbed personality and reduced attention. HE is minimal or grades I to IV (coma). Bouts of HE are episodic and often recurrent. Initial treatment is of events that precipitated the episode and exclusion of nonhepatic causes. Specific anti-HE treatment is lactulose. By recurrence, rifaximin is add-on. Anti-HE treatment is efficacious also for prophylaxis, but emergence of HE marks advanced liver disease and a dismal prognosis.

A late-onset hyperammonemia syndrome caused by Ureaplasma parvum infection after kidney transplantation.

Hyperammonemia syndrome has a high mortality rate in the immunosuppressed population due to its association with mental status changes. Recently studies have shown that Ureaplasma organisms' infection can lead to hyperammonemia in post-transplant patients. Symptoms typically occur within 30 days postoperatively. However, the late-onset hyperammonemia caused by Ureaplasma parvum infection after kidney transplantation has never been reported. In this case study, a 64-year-old Chinese male presented with symptoms such as nausea, vomiting, trouble sleeping, and deteriorating mental status 81 days after kidney transplantation. His plasma ammonia level was significantly elevated, and there was no evidence of liver synthetic dysfunction. Although common methods for ammonia clearance, such as haemodialysis and oral lactulose were initiated, his serum ammonia levels remained high. Metagenomic sequencing of serum determined Ureaplasma parvum infection. Levofloxacin and minocycline were administered respectively, which resulted in a decrease in ammonia levels, but normalization was not achieved. The computed tomographic scan revealed the presence of cerebral edema. Unfortunately, the patient eventually became brain dead with multiple organ failure. This case highlights that Ureaplasma parvum can cause late-onset hyperammonemia in kidney transplant patients. Once the mental status changes are identified, immediate empiric treatments should be initiated without waiting for a confirmed diagnosis of Ureaplasma spp. infection.

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.

Rare Pathogenic Variants in Pooled Whole-Exome Sequencing Data Suggest Hyperammonemia as a Possible Cause of Dementia Not Classified as Alzheimer's Disease or Frontotemporal Dementia.

The genetic bases of Alzheimer's disease (AD) and frontotemporal dementia (FTD) have been comprehensively studied, which is not the case for atypical cases not classified into these diagnoses. In the present study, we aim to contribute to the molecular understanding of the development of non-AD and non-FTD dementia due to hyperammonemia caused by mutations in urea cycle genes. The analysis was performed by pooled whole-exome sequencing (WES) of 90 patients and by searching for rare pathogenic variants in autosomal genes for enzymes or transporters of the urea cycle pathway. The survey returned two rare pathogenic coding mutations leading to citrullinemia type I: rs148918985, p.Arg265Cys, C>T; and rs121908641, p.Gly390Arg, G>A in the argininosuccinate synthase 1 (ASS1) gene. The p.Arg265Cys variant leads to enzyme deficiency, whereas p.Gly390Arg renders the enzyme inactive. These variants found in simple or compound heterozygosity can lead to the late-onset form of citrullinemia type I, associated with high ammonia levels, which can lead to cerebral dysfunction and thus to the development of dementia. The presence of urea cycle disorder-causing mutations can be used for the early initiation of antihyperammonemia therapy in order to prevent the neurotoxic effects.

Microbiota-gut-liver-brain axis and hepatic encephalopathy.

Hepatic encephalopathy (HE) is a clinical manifestation of neurological and psychiatric abnormalities that are caused by complications of liver dysfunction including hyperammonemia, hyperuricemia, and portal hypertension. Accumulating evidence suggests that HE could be reversed through therapeutic modifications of gut microbiota. Multiple preclinical and clinical studies have indicated that gut microbiome affects the physiological function of the liver, such as the regulation of metabolism, secretion, and immunity, through the gut-liver crosstalk. In addition, gut microbiota also influences the brain through the gut-brain crosstalk, altering its physiological functions including the regulation of the immune, neuroendocrine, and vagal pathways. Thus, key molecules that are involved in the microbiota-gut-liver-brain axis might be able to serve as clinical biomarkers for early diagnosis of HE, and could be effective therapeutic targets for clinical interventions. In this review, we summarize the pathophysiology of HE and further propose approaches modulating the microbiota-gut-liver-brain axis in order to provide a comprehensive understanding of the prevention and potential clinical treatment for HE with a microbiota-targeted therapy.