Defects in amino acid catabolism and the urea cycle

Cerebral White Matter Alterations Associated With Oligodendrocyte Vulnerability in Organic Acidurias: Insights in Glutaric Aciduria Type I

The white matter is an important constituent of the central nervous system, containing axons, oligodendrocytes, and its progenitor cells, astrocytes, and microglial cells. Oligodendrocytes are central for myelin synthesis, the insulating envelope that protects axons and allows normal neural conduction. Both, oligodendrocytes and myelin, are highly vulnerable to toxic factors in many neurodevelopmental and neurodegenerative disorders associated with disturbances of myelination. Here we review the main alterations in oligodendrocytes and myelin observed in some organic acidurias/acidemias, which correspond to inherited neurometabolic disorders biochemically characterized by accumulation of potentially neurotoxic organic acids and their derivatives. The yet incompletely understood mechanisms underlying the high vulnerability of OLs and/or myelin in glutaric acidemia type I, the most prototypical cerebral organic aciduria, are particularly discussed.

Understanding ayahuasca effects in major depressive disorder treatment through in vitro metabolomics and bioinformatics

Emerging insights from metabolomic-based studies of major depression disorder (MDD) are mainly related to biochemical processes such as energy or oxidative stress, in addition to neurotransmission linked to specific metabolite intermediates. Hub metabolites represent nodes in the biochemical network playing a critical role in integrating the information flow in cells between metabolism and signaling pathways. Limited technical-scientific studies have been conducted to understand the effects of ayahuasca (Aya) administration in the metabolism considering MDD molecular context. Therefore, this work aims to investigate an in vitro primary astrocyte model by untargeted metabolomics of two cellular subfractions: secretome and intracellular content after pre-defined Aya treatments, based on DMT concentration. Mass spectrometry (MS)-based metabolomics data revealed significant hub metabolites, which were used to predict biochemical pathway alterations. Branched-chain amino acid (BCAA) metabolism, and vitamin B6 and B3 metabolism were associated to Aya treatment, as "housekeeping" pathways. Dopamine synthesis was overrepresented in the network results when considering the lowest tested DMT concentration (1 µmol L^-1). Building reaction networks containing significant and differential metabolites, such as nicotinamide, L-DOPA, and L-leucine, is a useful approach to guide on dose decision and pathway selection in further analytical and molecular studies.

Long-term outcome of developmental and epileptic encephalopathies

Developmental and epileptic encephalopathies are conditions where there is developmental impairment related to both the underlying etiology independent of epileptiform activity and the epileptic encephalopathy. Usually they have multiple etiologies. Therefore, long-term outcome is related to both etiology-related factors and epilepsy-related factors-age at onset of epilepsy, type(s) of seizure(s), type of electroencephalographic abnormalities, duration of the epileptic disorder. This paper focuses on long-term outcome of six developmental and epileptic encephalopathies with onset from the neonatal period to childhood: early epileptic encephalopathy with suppression bursts, West syndrome, Dravet syndrome, Lennox-Gastaut syndrome, epilepsy with myoclonic atonic seizures and epileptic encephalopathy with continuous spike and waves during slow-wave sleep including Landau-Kleffner syndrome. For each syndrome, definition, main etiologies if multiple, and long-term outcome are discussed.

Stroke and stroke-like episodes in inborn errors of metabolism: Pathophysiological and clinical implications

Inborn errors of metabolism causing stroke (ischemic or haemorrhagic) or stroke-like episodes (e.g., that are also called "metabolic strokes" and include acute brain lesions not related with alterations of blood flow) cover a wide range of diseases in which acute metabolic decompensations after trigger events (e.g., fever, dehydration, sepsis etc.) may have a variable frequency. The early diagnosis of these conditions is essential because, despite their rarity, effective symptomatic treatments may be available for acute settings (e.g., arginine for Mitochondrial myopathy, Encephalopathy, Lactic Acidosis, and Stroke-like episodes- MELAS) while in other cases disease modifying therapies may be useful to prevent stroke occurrence, recurrence, or relapse (e.g., Fabry disease). The detection of a non-vascular distribution of lesions and the diffuse use of ¹HMRS are often diriment in the differential of ischemic and metabolic strokes. This review summarized the main clinical features and the pathophysiological mechanisms of stroke and stroke-like episodes in inborn errors of metabolism presenting with stroke as part of natural history of the disease. These conditions belong to different etiological groups, such as organic acidurias, mitochondrial encephalopathies, homocystinuria and remethylation disorders, urea cycle disorders, lysosomal diseases (e.g. Fabry disease, glycogen storage disease), congenital disorders of glycosylation, neurotransmitter disorders, adenosine deaminase 2 deficiency and few other neurometabolic disorders.

Extended Phenotyping and Functional Validation Facilitate Diagnosis of a Complex Patient Harboring Genetic Variants in MCCC1 and GNB5 Causing Overlapping Phenotypes

Identifying multiple ultra-rare genetic syndromes with overlapping phenotypes is a diagnostic conundrum in clinical genetics. This study investigated the pathogenicity of a homozygous missense variant in GNB5 (GNB5L; NM_016194.4: c.920T > G (p. Leu307Arg); GNB5S; NM_006578.4: c.794T > G (p. Leu265Arg)) identified through exome sequencing in a female child who also had 3-methylcrotonyl-CoA carboxylase (3-MCC) deficiency (newborn screening positive) and hemoglobin E trait. The proband presented with early-onset intellectual disability, the severity of which was more in keeping with GNB5-related disorder than 3-MCC deficiency. She later developed bradycardia and cardiac arrest, and upon re-phenotyping showed cone photo-transduction recovery deficit, all known only to GNB5-related disorders. Patient-derived fibroblast assays showed preserved GNB5S expression, but bioluminescence resonance energy transfer assay showed abolished function of the variant reconstituted Gβ5S containing RGS complexes for deactivation of D2 dopamine receptor activity, confirming variant pathogenicity. This study highlights the need for precise phenotyping and functional assays to facilitate variant classification and clinical diagnosis in patients with complex medical conditions.

Paroxysmal spasticity of lower extremities as the initial symptom in two siblings with maple syrup urine disease

Maple syrup urine disease (MSUD) is a rare autosomal recessive metabolic disorder caused by mutations in genes that encode subunits of the branched‑chain α‑ketoacid dehydrogenase (BCKD) complex. Impairment of the BCKD complex results in an abnormal accumulation of branched‑chain amino acids and their corresponding branched‑chain keto acids in the blood and cerebrospinal fluid, which are neurovirulent and may become life‑threatening. An 11‑day‑old boy was admitted to the hospital with paroxysmal spasticity of lower extremities. Of note, his 10‑year‑old sister presented similar symptoms during the neonatal period, and her condition was diagnosed as MSUD when she was 1.5 years old. Genetic screening was performed, and the boy and his sister exhibited two novel compound heterozygous mutations in the branched chain keto acid dehydrogenase E1 subunit β (BCKDHB) gene: A substitution from guanine to adenine in the coding region at position 1,076 (c.1,076G>A) in exon 10 and a deletion of a thymine at position 705 (c.705delT) in exon 6. The missense mutation c.1076G>A results in an amino acid substitution from arginine to lysine at position 359 (p.Arg359Lys), whereas the mutation c.705delT results in the replacement of a cysteine at position 235 with a stop codon (p.Cys235Ter). Neither of the BCKDHB alleles in the compound heterozygote patients is able to generate normal E1β subunits, resulting in a possible impairment of the activity of the BCKD complex. In the present study, it was hypothesized that the two novel heterozygous mutations in the BCKDHB gene found in the Chinese family may be responsible for the phenotype of the two siblings with MSUD.

The Transformative Possibilities of the Microbiota and Mycobiota for Health, Disease, Aging, and Technological Innovation

The gut microbiota is extremely important for the health of the host across its lifespan.Recent studies have elucidated connections between the gut microbiota and neurological diseaseand disorders such as depression, anxiety, Alzheimer's disease (AD), autism, and a host of otherbrain illnesses. Dysbiosis of the normal gut flora can have negative consequences for humans,especially throughout key periods during our lifespan as the gut microbes change with age in bothphenotype and number of bacterial species. Neurologic diseases, mental disorders, and euthymicstates are influenced by alterations in the metabolites produced by gut microbial milieu. Weintroduce a new concept, namely, the mycobiota and microbiota-gut-brain neuroendocrine axis anddiscuss co-metabolism with emphasis on means to influence or correct disruptions to normal gutflora throughout the lifespan from early development to old age. These changes involveinflammation and involve the permeability of barriers, such as the intestine blood barrier, the blood⁻brain barrier, and others. The mycobiota and microbiota⁻gut⁻brain axis offer new research horizonsand represents a great potential target for new therapeutics, including approaches based aroundinflammatory disruptive process, genetically engineered drug delivery systems, diseased cellculling "kill switches", phage-like therapies, medicinal chemistry, or microbial parabiosis to namea few.

Neuroimaging Findings of Organic Acidemias and Aminoacidopathies

Although individual cases of inherited metabolic disorders are rare, overall they account for a substantial number of disorders affecting the central nervous system. Organic acidemias and aminoacidopathies include a variety of inborn errors of metabolism that are caused by defects in the intermediary metabolic pathways of carbohydrates, amino acids, and fatty acid oxidation. These defects can lead to the abnormal accumulation of organic acids and amino acids in multiple organs, including the brain. Early diagnosis is mandatory to initiate therapy and prevent permanent long-term neurologic impairments or death. Neuroimaging findings can be nonspecific, and metabolism- and genetics-based laboratory investigations are needed to confirm the diagnosis. However, neuroimaging has a key role in guiding the diagnostic workup. The findings at conventional and advanced magnetic resonance imaging may suggest the correct diagnosis, help narrow the differential diagnosis, and consequently facilitate early initiation of targeted metabolism- and genetics-based laboratory investigations and treatment. Neuroimaging may be especially helpful for distinguishing organic acidemias and aminoacidopathies from other more common diseases with similar manifestations, such as hypoxic-ischemic injury and neonatal sepsis. Therefore, it is important that radiologists, neuroradiologists, pediatric neuroradiologists, and clinicians are familiar with the neuroimaging findings of organic acidemias and aminoacidopathies. ^©RSNA, 2018.

Acute Ataxia in Children: A Review of the Differential Diagnosis and Evaluation in the Emergency Department

Acute ataxia in a pediatric patient poses a diagnostic dilemma for any physician. While the most common etiologies are benign, occasional individuals require urgent intervention. Children with stroke, toxic ingestion, infection, and neuro-inflammatory disorders frequently exhibit ataxia as an essential-if not the only-presenting feature. The available retrospective research utilize inconsistent definitions of acute ataxia, precluding the ability to pool data from these studies. No prospective data exist that report on patients presenting to the emergency department with ataxia. This review examines the reported causes of ataxia and attempts to group them into distinct categories: post-infectious and inflammatory central and peripheral phenomena, toxic ingestion, neurovascular, infectious and miscellaneous. From there, we synthesize the existing literature to understand which aspects of the history, physical exam, and ancillary testing might aid in narrowing the differential diagnosis. MRI is superior to CT in detecting inflammatory or vascular insults in the posterior fossa, though CT may be necessary in emergent situations. Lumbar puncture may be deferred until after admission in most instances, with suspicion for meningitis being the major exception. There is insufficient evidence to guide laboratory evaluation of serum, testing should be ordered based on clinical judgement-recommended studies include metabolic profiles and screening labs for metabolic disorders (lactate and ammonia). All patients should be reflexively screened for toxic ingestions.

Carglumic acid enhances rapid ammonia detoxification in classical organic acidurias with a favourable risk-benefit profile: a retrospective observational study

Background

Isovaleric aciduria (IVA), propionic aciduria (PA) and methylmalonic aciduria (MMA) are inherited organic acidurias (OAs) in which impaired organic acid metabolism induces hyperammonaemia arising partly from secondary deficiency of N-acetylglutamate (NAG) synthase. Rapid reduction in plasma ammonia is required to prevent neurological complications. This retrospective, multicentre, open-label, uncontrolled, phase IIIb study evaluated the efficacy and safety of carglumic acid, a synthetic structural analogue of NAG, for treating hyperammonaemia during OA decompensation.

Methods

Eligible patients had confirmed OA and hyperammonaemia (plasma NH₃ > 60 μmol/L) in ≥1 decompensation episode treated with carglumic acid (dose discretionary, mean (SD) first dose 96.3 (73.8) mg/kg). The primary outcome was change in plasma ammonia from baseline to endpoint (last available ammonia measurement at ≤18 hours after the last carglumic acid administration, or on Day 15) for each episode. Secondary outcomes included clinical response and safety.

Results

The efficacy population (received ≥1 dose of study drug and had post-baseline measurements) comprised 41 patients (MMA: 21, PA: 16, IVA: 4) with 48 decompensation episodes (MMA: 25, PA: 19, IVA: 4). Mean baseline plasma ammonia concentration was 468.3 (±365.3) μmol/L in neonates (29 episodes) and 171.3 (±75.7) μmol/L in non-neonates (19 episodes). At endpoint the mean plasma NH₃ concentration was 60.7 (±36.5) μmol/L in neonates and 55.2 (±21.8) μmol/L in non-neonates. Median time to normalise ammonaemia was 38.4 hours in neonates vs 28.3 hours in non-neonates and was similar between OA subgroups (MMA: 37.5 hours, PA: 36.0 hours, IVA: 40.5 hours). Median time to ammonia normalisation was 1.5 and 1.6 days in patients receiving and not receiving concomitant scavenger therapy, respectively. Although patients receiving carglumic acid with scavengers had a greater reduction in plasma ammonia, the endpoint ammonia levels were similar with or without scavenger therapy. Clinical symptoms improved with therapy. Twenty-five of 57 patients in the safety population (67 episodes) experienced AEs, most of which were not drug-related. Overall, carglumic acid seems to have a good safety profile for treating hyperammonaemia during OA decompensation.

Conclusion

Carglumic acid when used with or without ammonia scavengers, is an effective treatment for restoration of normal plasma ammonia concentrations in hyperammonaemic episodes in OA patients.

Pharmacogenetics of antiepileptic drugs: A brief review

The goal of pharmacogenetic research is to assist clinicians in predicting patient response to medications when genetic variations are identified. The pharmacogenetic variation of antiepileptic drug response and side effects has yielded findings that have been included in drug labeling and guidelines. The goal of this review is to provide a brief overview of the pharmacogenetic research on antiepileptic drugs. It will focus on findings that have been included in drug labeling, guidelines, and candidate pharmacogenetic variation. Overall, several genes have been included in guidelines by national and international organizations; however, much work is needed to implement and evaluate their use in clinical settings.

Inborn Errors of Metabolism

Inborn errors of metabolism are single gene disorders resulting from the defects in the biochemical pathways of the body. Although these disorders are individually rare, collectively they account for a significant portion of childhood disability and deaths. Most of the disorders are inherited as autosomal recessive whereas autosomal dominant and X-linked disorders are also present. The clinical signs and symptoms arise from the accumulation of the toxic substrate, deficiency of the product, or both. Depending on the residual activity of the deficient enzyme, the initiation of the clinical picture may vary starting from the newborn period up until adulthood. Hundreds of disorders have been described until now and there has been a considerable clinical overlap between certain inborn errors. Resulting from this fact, the definite diagnosis of inborn errors depends on enzyme assays or genetic tests. Especially during the recent years, significant achievements have been gained for the biochemical and genetic diagnosis of inborn errors. Techniques such as tandem mass spectrometry and gas chromatography for biochemical diagnosis and microarrays and next-generation sequencing for the genetic diagnosis have enabled rapid and accurate diagnosis. The achievements for the diagnosis also enabled newborn screening and prenatal diagnosis. Parallel to the development the diagnostic methods; significant progress has also been obtained for the treatment. Treatment approaches such as special diets, enzyme replacement therapy, substrate inhibition, and organ transplantation have been widely used. It is obvious that by the help of the preclinical and clinical research carried out for inborn errors, better diagnostic methods and better treatment approaches will high likely be available.

Newborn Screening: What Does the Emergency Physician Need to Know?

Newborn screening programs were established in the United States in the early 1960s. Newborn screening programs were then developed by states and have continued to be the responsibility of the state. All states require a newborn screening, but what is required of these programs and screening panels has differed greatly by state. Historically, the most commonly screened disorders are the following: congenital hypothyroidism, congenital adrenal hyperplasia, sickle cell disease and associated hemoglobinopathies, biotinidase deficiency, galactosemia, cystic fibrosis and phenylketonuria, maple syrup urine disease, and homocystinuria. However, under new guidelines in 2006 and with new advances in technology, the scope of newborn screening programs has expanded to include at a minimum 9 organic acidurias, 5 fatty acid oxidation disorders, 3 hemoglobinopathies, and 6 other conditions. This CME article reviews the logistics of newborn screening and explores the effect of new technology and recent policy on state screens and what that means for providers. This article also highlights several of the disorders most relevant to emergency room physicians and discusses future considerations of newborn screening.

Neurometabolic diseases of childhood

Metabolic diseases affecting the pediatric brain are complex conditions, the underlying mechanisms leading to structural damage are diverse and the diagnostic imaging manifestations are often non-specific; hence early, sensitive and specific diagnosis can be challenging for the radiologist. However, misdiagnosis or a delayed diagnosis can result in a devastating, irreversible injury to the developing brain. Based upon the inborn error, neurometabolic diseases can be subdivided in various groups depending on the predominantly involved tissue (e.g., white matter in leukodystrophies or leukoencephalopathies), the involved metabolic processes (e.g., organic acidurias and aminoacidopathies) and primary age of the child at presentation (e.g., neurometabolic disorders of the newborn). This manuscript summarizes these topics.