Progress and challenges in development of new therapies for urea cycle disorders

Mitochondrial targets in hyperammonemia: Addressing urea cycle function to improve drug therapies

The urea cycle (UC) is a critically important metabolic process for the disposal of nitrogen (ammonia) produced by amino acids catabolism. The impairment of this liver-specific pathway induced either by primary genetic defects or by secondary causes, namely those associated with hepatic disease or drug administration, may result in serious clinical consequences. Urea cycle disorders (UCD) and certain organic acidurias are the major groups of inherited rare diseases manifested with hyperammonemia (HA) with UC dysregulation. Importantly, several commonly prescribed drugs, including antiepileptics in monotherapy or polytherapy from carbamazepine to valproic acid or specific antineoplastic agents such as asparaginase or 5-fluorouracil may be associated with HA by mechanisms not fully elucidated. HA, disclosing an imbalance between ammoniagenesis and ammonia disposal via the UC, can evolve to encephalopathy which may lead to significant morbidity and central nervous system damage. This review will focus on biochemical mechanisms related with HA emphasizing some poorly understood perspectives behind the disruption of the UC and mitochondrial energy metabolism, namely: i) changes in acetyl-CoA or NAD+ levels in subcellular compartments; ii) post-translational modifications of key UC-related enzymes, namely acetylation, potentially affecting their catalytic activity; iii) the mitochondrial sirtuins-mediated role in ureagenesis. Moreover, the main UCD associated with HA will be summarized to highlight the relevance of investigating possible genetic mutations to account for unexpected HA during certain pharmacological therapies. The ammonia-induced effects should be avoided or overcome as part of safer therapeutic strategies to protect patients under treatment with drugs that may be potentially associated with HA.

In vitro characterization of 3D culture-based differentiation of human liver stem cells

Introduction: The lack of functional hepatocytes poses a significant challenge for drug safety testing and therapeutic applications due to the inability of mature hepatocytes to expand and their tendency to lose functionality in vitro. Previous studies have demonstrated the potential of Human Liver Stem Cells (HLSCs) to differentiate into hepatocyte-like cells within an in vitro rotary cell culture system, guided by a combination of growth factors and molecules known to regulate hepatocyte maturation. In this study, we employed a matrix multi-assay approach to comprehensively characterize HLSC differentiation. Methods: We evaluated the expression of hepatic markers using qRT-PCR, immunofluorescence, and Western blot analysis. Additionally, we measured urea and FVIII secretion into the supernatant and developed an updated indocyanine green in vitro assay to assess hepatocyte functionality. Results: Molecular analyses of differentiated HLSC aggregates revealed significant upregulation of hepatic genes, including CYP450, urea cycle enzymes, and uptake transporters exclusively expressed on the sinusoidal side of mature hepatocytes, evident as early as 1 day post-differentiation. Interestingly, HLSCs transiently upregulated stem cell markers during differentiation, followed by downregulation after 7 days. Furthermore, differentiated aggregates demonstrated the ability to release urea and FVIII into the supernatant as early as the first 24 h, with accumulation over time. Discussion: These findings suggest that a 3D rotation culture system may facilitate rapid hepatic differentiation of HLSCs. Despite the limitations of this rotary culture system, its unique advantages hold promise for characterizing HLSC GMP batches for clinical applications.

Development of a Two-Dimensional Liquid Chromatographic Method for Analysis of Urea Cycle Amino Acids

The urea cycle has been found to be closely associated with certain types of cancers and other diseases such as cardiovascular disease and chronic kidney disease. An analytical method for the precise quantification of urea cycle amino acids (arginine, ornithine, citrulline, and argininosuccinate) by off-line two-dimensional liquid chromatography (2D-LC) combined with fluorescence-based detection was developed. Before analysis, the amino acids were derivatised with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) to obtain NBD-amino acids. The first dimension involved the reversed-phase separation, in which NBD derivatives of urea cycle amino acids were completely separated from each other and mostly separated from the 18 NBD-proteinogenic amino acids. The samples were eluted with stepwise gradient using 0.02% trifluoroacetic acid in water-acetonitrile as the mobile phase. In the second dimension, an amino column was used for the separation of NBD-ornithine, -citrulline, and -argininosuccinate, while a sulfonic acid column was used to separate NBD-arginine. The developed 2D-LC system was used to analyse human plasma samples. The fractions of NBD-urea cycle amino acids obtained in the first dimension were collected manually and introduced into the second dimension. By choosing appropriate mobile phases for the second dimension, each NBD-urea cycle amino acid eluted in the first dimension was well separated from the other proteinogenic amino acids and interference from endogenous substance. This could not be achieved in the first dimension. The urea cycle amino acids in human plasma sample were quantified, and the method was well validated. The calibration curves for each NBD-urea cycle amino acid showed good linearity from 3 (ASA) or 15 (Orn, Cit, and Arg) to 600 nM, with correlation coefficients higher than 0.9969. The intraday and interday precisions were less than 7.9% and 15%, respectively. The 2D-LC system is expected to be useful for understanding the involvement of the urea cycle in disease progression.

Clinical and biochemical footprints of inherited metabolic diseases. XV. Epilepsies

We provide a comprehensive overview of inherited metabolic disorders (IMDs) in which epilepsy is a prominent manifestation. Our unique database search has identified 256 IMDs associated with various types of epilepsies, which we classified according to the classic pathophysiology-based classification of IMDs, and according to selected seizure-related factors (neonatal seizures, infantile spasms, myoclonic seizures, and characteristic EEG patterns) and treatability for the underlying metabolic defect. Our findings indicate that inherited metabolic epilepsies are more likely to present in the neonatal period, with infantile spasms or myoclonic seizures. Additionally, the ∼20% of treatable inherited metabolic epilepsies found by our search were mainly associated with the IMD groups of "cofactor and mineral metabolism" and "Intermediary nutrient metabolism." The information provided by this study, including a comprehensive list of IMDs with epilepsy stratified according to age of onset, and seizure type and characteristics, along with an overview of the key clinical features and proposed diagnostic and therapeutic approaches, may benefit any epileptologist and healthcare provider caring for individuals with metabolic conditions.

Diagnostic and Management Issues in Patients with Late-Onset Ornithine Transcarbamylase Deficiency

Ornithine transcarbamylase deficiency (OTCD) is the most common inherited disorder of the urea cycle and, in general, is transmitted as an X-linked recessive trait. Defects in the OTC gene cause an impairment in ureagenesis, resulting in hyperammonemia, which is a direct cause of brain damage and death. Patients with late-onset OTCD can develop symptoms from infancy to later childhood, adolescence or adulthood. Clinical manifestations of adults with OTCD vary in acuity. Clinical symptoms can be aggravated by metabolic stressors or the presence of a catabolic state, or due to increased demands upon the urea. A prompt diagnosis and relevant biochemical and genetic investigations allow the rapid introduction of the right treatment and prevent long-term complications and mortality. This narrative review outlines challenges in diagnosing and managing patients with late-onset OTCD.

Genetics of enzymatic dysfunctions in metabolic disorders and cancer

Inherited metabolic disorders arise from mutations in genes involved in the biogenesis, assembly, or activity of metabolic enzymes, leading to enzymatic deficiency and severe metabolic impairments. Metabolic enzymes are essential for the normal functioning of cells and are involved in the production of amino acids, fatty acids and nucleotides, which are essential for cell growth, division and survival. When the activity of metabolic enzymes is disrupted due to mutations or changes in expression levels, it can result in various metabolic disorders that have also been linked to cancer development. However, there remains much to learn regarding the relationship between the dysregulation of metabolic enzymes and metabolic adaptations in cancer cells. In this review, we explore how dysregulated metabolism due to the alteration or change of metabolic enzymes in cancer cells plays a crucial role in tumor development, progression, metastasis and drug resistance. In addition, these changes in metabolism provide cancer cells with a number of advantages, including increased proliferation, resistance to apoptosis and the ability to evade the immune system. The tumor microenvironment, genetic context, and different signaling pathways further influence this interplay between cancer and metabolism. This review aims to explore how the dysregulation of metabolic enzymes in specific pathways, including the urea cycle, glycogen storage, lysosome storage, fatty acid oxidation, and mitochondrial respiration, contributes to the development of metabolic disorders and cancer. Additionally, the review seeks to shed light on why these enzymes represent crucial potential therapeutic targets and biomarkers in various cancer types.

Treatment of neurometabolic epilepsies: Overview and recent advances

The rarity and heterogeneity of neurometabolic diseases make it challenging to reach evidence-based principles for their specific treatments. Indeed, current treatments for many of these diseases remain symptomatic and supportive. However, an ongoing scientific and medical revolution has led to dramatic breakthroughs in molecular sciences and genetics, revealing precise pathophysiologic mechanisms. Accordingly, this has led to significant progress in the development of novel therapeutic approaches aimed at treating epilepsy resulting from these conditions, as well as their other manifestations. We overview recent notable treatment advancements, from vitamins, trace minerals, and diets to unique medications targeting the elemental pathophysiology at a molecular or cellular level, including enzyme replacement therapy, enzyme enhancing therapy, antisense oligonucleotide therapy, stem cell transplantation, and gene therapy.

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

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

Challenges of managing ornithine transcarbamylase deficiency in female heterozygotes

Urea cycle disorders (UCDs) are a group of rare inherited metabolic conditions caused by enzyme deficiency within the hepatic ammonia detoxification pathway. Ornithine transcarbamylase (OTC) deficiency, the most frequently occurring UCD, is an X-linked condition known to yield a vastly heterogeneous phenotype, with variable onset and presentation across the lifespan. Here, we introduce a series of 4 original cases, published as part of this special supplement, that illustrate learnings for the care of heterozygous females with OTC deficiency, including challenges with diagnosis, potential triggers of hyperammonemia, cognitive effects, and approaches to disease management, including peripartum care.

Current status and future directions of clinical applications using iPS cells-focus on Japan

Regenerative medicine using iPS cell technologies has progressed remarkably in recent years. In this review, we summarize these technologies and their clinical application. First, we discuss progress in the establishment of iPS cells, including the HLA-homo iPS cell stock project in Japan and the advancement of low antigenic iPS cells using genome-editing technology. Then, we describe iPS cell-based therapies in or approaching clinical application, including those for ophthalmological, neurological, cardiac, hematological, cartilage, and metabolic diseases. Next, we introduce disease models generated from patient iPS cells and successfully used to identify therapeutic agents for intractable diseases. Clinical medicine using iPS cells has advanced safely and effectively by making full use of current scientific standards, but tests on cell safety need to be further developed and validated. The next decades will see the further spread of iPS cell technology-based regenerative medicine.

O-GlcNAcylation enhances CPS1 catalytic efficiency for ammonia and promotes ureagenesis

Life-threatening hyperammonemia occurs in both inherited and acquired liver diseases affecting ureagenesis, the main pathway for detoxification of neurotoxic ammonia in mammals. Protein O-GlcNAcylation is a reversible and nutrient-sensitive post-translational modification using as substrate UDP-GlcNAc, the end-product of hexosamine biosynthesis pathway. Here we show that increased liver UDP-GlcNAc during hyperammonemia increases protein O-GlcNAcylation and enhances ureagenesis. Mechanistically, O-GlcNAcylation on specific threonine residues increased the catalytic efficiency for ammonia of carbamoyl phosphate synthetase 1 (CPS1), the rate-limiting enzyme in ureagenesis. Pharmacological inhibition of O-GlcNAcase, the enzyme removing O-GlcNAc from proteins, resulted in clinically relevant reductions of systemic ammonia in both genetic (hypomorphic mouse model of propionic acidemia) and acquired (thioacetamide-induced acute liver failure) mouse models of liver diseases. In conclusion, by fine-tuned control of ammonia entry into ureagenesis, hepatic O-GlcNAcylation of CPS1 increases ammonia detoxification and is a novel target for therapy of hyperammonemia in both genetic and acquired diseases.

Aquaporin 9 induction in human iPSC-derived hepatocytes facilitates modeling of ornithine transcarbamylase deficiency

BACKGROUND AND AIMS

Patient-derived human-induced pluripotent stem cells (hiPSCs) differentiated into hepatocytes (hiPSC-Heps) have facilitated the study of rare genetic liver diseases. Here, we aimed to establish an in vitro liver disease model of the urea cycle disorder ornithine transcarbamylase deficiency (OTCD) using patient-derived hiPSC-Heps.

APPROACH AND RESULTS

Before modeling OTCD, we addressed the question of why hiPSC-Heps generally secrete less urea than adult primary human hepatocytes (PHHs). Because hiPSC-Heps are not completely differentiated and maintain some characteristics of fetal PHHs, we compared gene-expression levels in human fetal and adult liver tissue to identify genes responsible for reduced urea secretion in hiPSC-Heps. We found lack of aquaporin 9 (AQP9) expression in fetal liver tissue as well as in hiPSC-Heps, and showed that forced expression of AQP9 in hiPSC-Heps restores urea secretion and normalizes the response to ammonia challenge by increasing ureagenesis. Furthermore, we proved functional ureagenesis by challenging AQP9-expressing hiPSC-Heps with ammonium chloride labeled with the stable isotope [¹⁵ N] (¹⁵ NH₄ Cl) and by assessing enrichment of [¹⁵ N]-labeled urea. Finally, using hiPSC-Heps derived from patients with OTCD, we generated a liver disease model that recapitulates the hepatic manifestation of the human disease. Restoring OTC expression-together with AQP9-was effective in fully correcting OTC activity and normalizing ureagenesis as assessed by ¹⁵ NH₄ Cl stable-isotope challenge.

CONCLUSION

Our results identify a critical role for AQP9 in functional urea metabolism and establish the feasibility of in vitro modeling of OTCD with hiPSC-Heps. By facilitating studies of OTCD genotype/phenotype correlation and drug screens, our model has potential for improving the therapy of OTCD.

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

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

Ornithine Transcarbamylase - From Structure to Metabolism: An Update

Ornithine transcarbamylase (OTC; EC 2.1.3.3) is a ubiquitous enzyme found in almost all organisms, including vertebrates, microorganisms, and plants. Anabolic, mostly trimeric OTCs catalyze the production of L-citrulline from L-ornithine which is a part of the urea cycle. In eukaryotes, such OTC localizes to the mitochondrial matrix, partially bound to the mitochondrial inner membrane and part of channeling multi-enzyme assemblies. In mammals, mainly two organs express OTC: the liver, where it is an integral part of the urea cycle, and the intestine, where it synthesizes citrulline for export and plays a major role in amino acid homeostasis, particularly of L-glutamine and L-arginine. Here, we give an overview on OTC genes and proteins, their tissue distribution, regulation, and physiological function, emphasizing the importance of OTC and urea cycle enzymes for metabolic regulation in human health and disease. Finally, we summarize the current knowledge of OTC deficiency, a rare X-linked human genetic disorder, and its emerging role in various chronic pathologies.

Hyperammonemia in Inherited Metabolic Diseases

Ammonia is a neurotoxic compound which is detoxified through liver enzymes from urea cycle. Several inherited or acquired conditions can elevate ammonia concentrations in blood, causing severe damage to the central nervous system due to the toxic effects exerted by ammonia on the astrocytes. Therefore, hyperammonemic patients present potentially life-threatening neuropsychiatric symptoms, whose severity is related with the hyperammonemia magnitude and duration, as well as the brain maturation stage. Inherited metabolic diseases caused by enzymatic defects that compromise directly or indirectly the urea cycle activity are the main cause of hyperammonemia in the neonatal period. These diseases are mainly represented by the congenital defects of urea cycle, classical organic acidurias, and the defects of mitochondrial fatty acids oxidation, with hyperammonemia being more severe and frequent in the first two groups mentioned. An effective and rapid treatment of hyperammonemia is crucial to prevent irreversible neurological damage and it depends on the understanding of the pathophysiology of the diseases, as well as of the available therapeutic approaches. In this review, the mechanisms underlying the hyperammonemia and neurological dysfunction in urea cycle disorders, organic acidurias, and fatty acids oxidation defects, as well as the therapeutic strategies for the ammonia control will be discussed.

Human Liver Stem Cells: A Liver-Derived Mesenchymal Stromal Cell-Like Population With Pro-regenerative Properties

Human liver stem cells (HLSCs) were described for the first time in 2006 as a new stem cell population derived from healthy human livers. Like mesenchymal stromal cells, HLSCs exhibit multipotent and immunomodulatory properties. HLSCs can differentiate into several lineages under defined in vitro conditions, such as mature hepatocytes, osteocytes, endothelial cells, and islet-like cell organoids. Over the years, HLSCs have been shown to contribute to tissue repair and regeneration in different in vivo models, leading to more than five granted patents and over 15 peer reviewed scientific articles elucidating their potential therapeutic role in various experimental pathologies. In addition, HLSCs have recently completed a Phase 1 study evaluating their safety post intrahepatic injection in infants with inherited neonatal onset hyperammonemia. Even though a lot of progress has been made in understanding HLSCs over the past years, some important questions regarding the mechanisms of action remain to be elucidated. Among the mechanisms of interaction of HLSCs with their environment, a paracrine interface has emerged involving extracellular vesicles (EVs) as vehicles for transferring active biological materials. In our group, the EVs derived from HLSCs have been studied in vitro as well as in vivo. Our attention has mainly been focused on understanding the in vivo ability of HLSC–derived EVs as modulators of tissue regeneration, inflammation, fibrosis, and tumor growth. This review article aims to discuss in detail the role of HLSCs and HLSC-EVs in these processes and their possible future therapeutic applications.

Beclin-1-mediated activation of autophagy improves proximal and distal urea cycle disorders

Urea cycle disorders (UCD) are inherited defects in clearance of waste nitrogen with high morbidity and mortality. Novel and more effective therapies for UCD are needed. Studies in mice with constitutive activation of autophagy unravelled Beclin-1 as druggable candidate for therapy of hyperammonemia. Next, we investigated efficacy of cell-penetrating autophagy-inducing Tat-Beclin-1 (TB-1) peptide for therapy of the two most common UCD, namely ornithine transcarbamylase (OTC) and argininosuccinate lyase (ASL) deficiencies. TB-1 reduced urinary orotic acid and improved survival under protein-rich diet in spf-ash mice, a model of OTC deficiency (proximal UCD). In AslNeo/Neo mice, a model of ASL deficiency (distal UCD), TB-1 increased ureagenesis, reduced argininosuccinate, and improved survival. Moreover, it alleviated hepatocellular injury and decreased both cytoplasmic and nuclear glycogen accumulation in AslNeo/Neo mice. In conclusion, Beclin-1-dependent activation of autophagy improved biochemical and clinical phenotypes of proximal and distal defects of the urea cycle.

Glycerol phenylbutyrate efficacy and safety from an open label study in pediatric patients under 2 months of age with urea cycle disorders

BACKGROUND/AIMS

Neonatal onset Urea cycle disorders (UCDs) can be life threatening with severe hyperammonemia and poor neurological outcomes. Glycerol phenylbutyrate (GPB) is safe and effective in reducing ammonia levels in patients with UCD above 2 months of age. This study assesses safety, ammonia control and pharmacokinetics (PK) of GPB in UCD patients below 2 months of age.

METHODS

This was an open-label study in UCD patients aged 0 - 2 months, consisting of an initiation/transition period (1 - 4 days) to GPB, followed by a safety extension period (6 months to 2 years). Patients presenting with a hyperammonemic crisis (HAC) did not initiate GPB until blood ammonia levels decreased to below 100 µmol/L while receiving sodium phenylacetate/sodium benzoate and/or hemodialysis. Ammonia levels, PK analytes and safety were evaluated during transition and monthly during the safety extension for 6 months and every 3 months thereafter.

RESULTS

All 16 patients with UCD (median age 0.48 months, range 0.1 to 2.0 months) successfully transitioned to GPB within 3 days. Average plasma ammonia level excluding HAC was 94.3 µmol/L at baseline and 50.4 µmol/L at the end of the transition period (p = 0.21). No patient had a HAC during the transition period. During the safety extension, the majority of patients had controlled ammonia levels, with mean plasma ammonia levels lower during GPB treatment than baseline. Mean glutamine levels remained within normal limits throughout the study. PK analyses indicate that UCD patients <2 months are able to hydrolyze GPB with subsequent absorption of phenylbutyric acid (PBA), metabolism to phenylacetic acid (PAA) and conjugation with glutamine. Plasma concentrations of PBA, PAA, and phenylacetylglutamine (PAGN) were stable during the safety extension phase and mean plasma phenylacetic acid: phenylacetylglutamine ratio remained below 2.5 suggesting no accumulation of GPB. All patients reported at least 1 treatment emergent adverse event with gastroesophageal reflux disease, vomiting, hyperammonemia, diaper dermatitis (37.5% each), diarrhea, upper respiratory tract infection and rash (31.3% each) being the most frequently reported.

CONCLUSIONS

This study supports safety and efficacy of GPB in UCD patients aged 0 -2 months who cannot be managed by dietary protein restriction and/or amino acid supplementation alone. GPB undergoes intestinal hydrolysis with no accumulation in this population.

A primer to gene therapy: Progress, prospects, and problems

Genetic therapies based on gene addition have witnessed a variety of clinical successes and the first therapeutic products have been approved for clinical use. Moreover, innovative gene editing techniques are starting to offer new opportunities in which the mutations that underlie genetic diseases can be directly corrected in afflicted somatic cells. The toolboxes underpinning these DNA modifying technologies are expanding with great pace. Concerning the ongoing efforts for their implementation, viral vector-based gene delivery systems have acquired center-stage, providing new hopes for patients with inherited and acquired disorders. Specifically, the application of genetic therapies using viral vectors for the treatment of inborn metabolic disorders is growing and clinical applications are starting to appear. While the field has matured from the technology perspective and has yielded efficacious products, it is the perception of many stakeholders that from the regulatory side further developments are urgently needed. In this review, we summarize the features of state-of-the-art viral vector systems and the corresponding gene-centered therapies they seek to deliver. Moreover, a brief summary is also given on emerging gene editing approaches built on CRISPR-Cas9 nucleases and, more recently, nickases, including base editors and prime editors. Finally, we will point at some regulatory aspects that may deserve further attention for translating these technological developments into actual advanced therapy medicinal products (ATMPs).

Treating epilepsy with options other than antiepileptic medications

Epilepsy is a common health burden worldwide. Epilepsy is linked to variety of factors, including infectious, vascular, immune, structural, genetic, and metabolic etiologies. Despite the existence of multiple antiepileptic drugs (AEDs), many patients are diagnosed with intractable epilepsy. Many nonpharmacological options are available for epilepsy. Some types of epilepsy respond to cofactors. Other patients may be candidates for a ketogenic diet. Inflammatory mediators, such as intravenous immunoglobulins (IVIgs) and steroids, are other options for epilepsy. Recently, cannabinoids have been approved for epilepsy treatment. Refractory epilepsy can be treated with surgical interventions. Focal resections, hemispherectomies, and corpus callosotomies are some common epilepsy surgery approaches. Neuromodulation techniques are another option. Thermal ablation is a minimally invasive approach for epilepsy treatment. Epilepsy outcomes are improving, and treatment modalities are expanding. Trials of nonpharmacological options for epilepsy patients are recommended. This article summarizes available nonpharmacological options other than AEDs for the treatment of epilepsy.

Established and Emerging Treatments for Patients with Inborn Errors of Metabolism

Inborn errors of metabolism (IEMs) are inherited defects in a metabolic pathway resulting in clinical disease. The overall goal of therapy is to restore metabolic homeostasis while minimizing the deleterious effects of the interruption. Conventional treatments focus on decreasing substrate, providing product, and replacing deficient enzyme or cofactor. We discuss examples of established, novel, and emerging therapies to provide a framework for understanding the principles of management for patients with IEMs.