Update current understanding of neurometabolic disorders related to lysine metabolism.

Lysine, as an essential amino acid, predominantly undergoes metabolic processes through the saccharopine pathway, whereas a smaller fraction follows the pipecolic acid pathway. Although the liver is considered the primary organ for lysine metabolism, it is worth noting that lysine catabolism also takes place in other tissues and organs throughout the body, including the brain. Enzyme deficiency caused by pathogenic variants in its metabolic pathway may lead to a series of neurometabolic diseases, among which glutaric aciduria type 1 and pyridoxine-dependent epilepsy have the most significant clinical manifestations. At present, through research, we have a deeper understanding of the multiple pathophysiological mechanisms related to these diseases, including intracerebral accumulation of neurotoxic metabolites, imbalance between GABAergic and glutamatergic neurotransmission, energy deprivation due to metabolites, and the dysfunction of antiquitin. Because of the complexity of these diseases, their clinical manifestations are also diverse. The early implementation of lysine-restricted diets and supplementation with arginine and carnitine has reported positive impacts on the neurodevelopmental outcomes of patients. Presently, there is more robust evidence supporting the effectiveness of these treatments in glutaric aciduria type 1 compared with pyridoxine-dependent epilepsy.

Hyponatremia Treatment Guidelines - Have They Gone Too Far?

Hyponatremia is a common electrolyte abnormality affecting hospitalized patients.1 It is an independent predictor for mortality and is associated with increased length of hospital stay and higher costs. The most serious potential complication is hyponatremic encephalopathy, a medical emergency that can result in death or irreversible brain injury if inadequately treated.2 Hypertonic saline is a safe and effective means of correcting hyponatremia.2-4 A rare yet serious complication from excessive correction of chronic hyponatremia is the development of cerebral demyelination.

Profound Hypercalcemia Associated with Acute Toxic-Metabolic Encephalopathy After Calcium Sulfate Bead Use: A Case Report.

CASE: We present the case of an 81-year-old woman who developed profound hypercalcemia requiring admission to the intensive care unit after calcium sulfate bead use during revision hip arthroplasty. The patient's serum calcium level peaked at 21.0 mg/dL and was associated with acute encephalopathy. After treatment with calcitonin and bisphosphonates, her serum calcium level normalized and her mentation improved. CONCLUSION: The risk of clinically significant hypercalcemia should be considered when using calcium sulfate during orthopaedic surgery.

Intersections in Neuropsychiatric and Metabolic Disorders: Possible Role of TRPA1 Channels.

Neuropsychiatric disorders (NPDs) are a huge burden to the patient, their family, and society. NPDs have been greatly associated with cardio-metabolic comorbidities such as obesity, type-2 diabetes mellitus, dysglycaemia, insulin resistance, dyslipidemia, atherosclerosis, and other cardiovascular disorders. Antipsychotics, which are frontline drugs in the treatment of schizophrenia and off-label use in other NPDs, also add to this burden by causing severe metabolic perturbations. Despite decades of research, the mechanism deciphering the link between neuropsychiatric and metabolic disorders is still unclear. In recent years, transient receptor potential Ankyrin 1 (TRPA1) channel has emerged as a potential therapeutic target for modulators. TRPA1 agonists/antagonists have shown efficacy in both neuropsychiatric disorders and appetite regulation and thus provide a crucial link between both. TRPA1 channels are activated by compounds such as cinnamaldehyde, allyl isothiocyanate, allicin and methyl syringate, which are present naturally in food items such as cinnamon, wasabi, mustard, garlic, etc. As these are present in many daily food items, it could also improve patient compliance and reduce the patients' monetary burden. In this review, we have tried to present evidence of the possible involvement of TRPA1 channels in neuropsychiatric and metabolic disorders and a possible hint towards using TRPA1 modulators to target appetite, lipid metabolism, glucose and insulin homeostasis and inflammation associated with NPDs.

The biochemical subtype is a predictor for cognitive function in glutaric aciduria type 1: a national prospective follow-up study.

The aim of the study was a systematic evaluation of cognitive development in individuals with glutaric aciduria type 1 (GA1), a rare neurometabolic disorder, identified by newborn screening in Germany. This national, prospective, observational, multi-centre study includes 107 individuals with confirmed GA1 identified by newborn screening between 1999 and 2020 in Germany. Clinical status, development, and IQ were assessed using standardized tests. Impact of interventional and non-interventional parameters on cognitive outcome was evaluated. The majority of tested individuals (n = 72) showed stable IQ values with age (n = 56 with IQ test; median test age 11 years) but a significantly lower performance (median [IQR] IQ 87 [78-98]) than in general population, particularly in individuals with a biochemical high excreter phenotype (84 [75-96]) compared to the low excreter group (98 [92-105]; p = 0.0164). For all patients, IQ results were homogenous on subscale levels. Sex, clinical motor phenotype and quality of metabolic treatment had no impact on cognitive functions. Long-term neurologic outcome in GA1 involves both motor and cognitive functions. The biochemical high excreter phenotype is the major risk factor for cognitive impairment while cognitive functions do not appear to be impacted by current therapy and striatal damage. These findings implicate the necessity of new treatment concepts.

Subdural hematoma in glutaric aciduria type 1: High excreters are prone to incidental SDH despite newborn screening.

Subdural hematoma (SDH) was initially reported in 20% to 30% of patients with glutaric aciduria type 1 (GA1). A recent retrospective study found SDH in 4% of patients, but not in patients identified by newborn screening (NBS). 168 MRIs of 69 patients with GA1 (age at MRI 9 days - 73.8 years, median 3.2 years) were systematically reviewed for presence of SDH, additional MR and clinical findings in order to investigate the frequency of SDH and potential risk factors. SDH was observed in eight high-excreting patients imaged between 5.8 and 24.4 months, namely space-occupying SDH in two patients after minor accidental trauma and SDH as an incidental finding in six patients without trauma. In patients without trauma imaged at 3 to 30 months (n = 36, 25 NBS, 27/9 high/low excreters), incidence of SDH was 16.7% (16% in NBS). SDH was more common after acute (33.3%) than insidious onset of dystonia (14.3%) or in asymptomatic patients (5.9%). It was only seen in patients with wide frontoparietal CSF spaces and frontotemporal hypoplasia. High excreters were over-represented among patients with SDH (6/27 vs 0/9 low excreters), acute onset (10/12), and wide frontoparietal CSF spaces (16/19). Incidental SDH occurs despite NBS and early treatment in approximately one in six patients with GA1 imaged during late infancy and early childhood. Greater risk of high excreters is morphologically associated with more frequent enlargement of external CSF spaces including frontotemporal hypoplasia, and may be furthered aggravated by more pronounced alterations of cerebral blood volume and venous pressure.

COVID-19 triggered encephalopathic crisis in a patient with glutaric aciduria type 1.

OBJECTIVES: The impact of coronavirus disease-19 (COVID-19) on metabolic outcome in patients with inborn errors of metabolism has rarely been discussed. Herein, we report a case with an acute encephalopathic crisis at the course of COVID-19 disease as the first sign of glutaric aciduria type 1 (GA-1). CASE PRESENTATION: A 9-month-old patient was admitted with encephalopathy and acute loss of acquired motor skills during the course of COVID-19 disease. She had lethargy, hypotonia, and choreoathetoid movements. In terms of COVID-19 encephalopathy, the reverse transcription-polymerase chain reaction assay test for COVID-19 was negative in cerebral spinal fluid. Brain imaging showed frontotemporal atrophy, bilateral subcortical and periventricular white matter, basal ganglia, and thalamic involvement. Elevated glutarylcarnitine in plasma and urinary excretion of glutaric and 3-OH-glutaric acids was noted. A homozygote mutation in the glutaryl-CoA dehydrogenase gene led to the diagnosis of GA-1. CONCLUSIONS: With this report, neurological damage associated with COVID-19 has been reported in GA-1 patients for the first time in literature.

Rhabdomyolysis, Acute Kidney Injury, and a Novel Frameshift Mutation in a Child with Glutaric Acidemia Type I.

This is a case report of a girl with glutaric acidemia type I (GA-I) who experienced rhabdomyolysis and acute kidney injury (AKI). Her first acute metabolic crisis occurred at the age of 5 months, which mainly manifested as irritable crying, poor appetite, and hyperlactatemia. Mutation analysis showed 2 pathogenic mutations in the glutaryl-CoA dehydrogenase (GCDH) gene, which were c.383G>A (p.R128Q) and c.873delC (p.N291Kfs*41), the latter of which is a novel frameshift mutation of GA-I. She had a febrile illness at the age of 12 months, followed by AKI and severe rhabdomyolysis. Four days of continuous venovenous hemodiafiltration (CVVHDF) helped to overcome this acute decompensation. This case report describes a novel mutation in the GCDH gene, that is, c.873delC (p.N291Kfs*41). Also, it highlights the fact that patients with GA-I have a high risk of rhabdomyolysis and AKI, which may be induced by febrile diseases and hyperosmotic dehydration; CVVHDF can help to overcome this acute decompensation.

Orthopaedic Problems in 35 Patients With Organic Acid Disorders.

INTRODUCTION: Organic acid disorders (OADs) are a subset of inborn errors of metabolism that result in a toxic accumulation of organic acids in the body, which can lead to metabolic derangements and encephalopathy. Patients with these disorders are managed by a team of biochemical geneticists and metabolic nutritionists. However, subspecialists such as neurologists and orthopaedic surgeons are often needed to help manage the sequelae of the metabolic derangements. The breadth of orthopaedic sequelae of these disease states is poorly understood. Herein, we describe orthopaedic problems associated with 5 types of OAD most commonly seen at our institution: maple syrup urine disease, methylmalonic aciduria, propionic aciduria, pyruvate dehydrogenase deficiency, and glutaric aciduria type 1. METHODS: We retrospectively reviewed medical records of 35 patients with an OAD who were seen at our academic tertiary care center from May 1999 to May 2020. Patients were grouped into cohorts according to OAD type and analyzed for orthopaedic presentations of hip, knee, or foot disorders, presence and severity of scoliosis, history of fracture, movement disorders, and osteopenia/osteoporosis. RESULTS: Of the 35 patients, 13 had maple syrup urine disease, 12 had methylmalonic aciduria, 4 had propionic aciduria, 4 had pyruvate dehydrogenase deficiency, and 2 had glutaric aciduria type 1. Associated orthopaedic problems included spasticity causing neuromuscular scoliosis and/or hip subluxation or dislocation (10 patients), fractures (7 patients), and osteopenia/osteoporosis (7 patients). Overall, 22 of 35 patients had some orthopaedic condition. CONCLUSIONS: Most in this cohort of patients with OAD also had an orthopaedic abnormality. It is important for physicians treating these patients to understand their propensity for musculoskeletal problems. When treating patients with OAD, it is important to initiate and maintain communication with specialists in several disciplines and to develop collaborative treatments for this unique population. LEVEL OF EVIDENCE: Level IV-prognostic study.

Management of COVID-19 infection in organic acidemias.

The COVID-19 pandemic has affected the health and healthcare of individuals of all ages worldwide. There have been multiple reports and reviews documenting a milder effect and decreased morbidity and mortality in the pediatric population, but there have only been a small number of reports discussing the SARS-CoV-2 infection in the setting of an inborn error of metabolism (IEM). Here, we report two patients with underlying metabolic disorders, propionic acidemia and glutaric aciduria type 1, and discuss their clinical presentation, as well as their infectious and metabolic management. Our report demonstrates that individuals with an underlying IEM are at risk of metabolic decompensation in the setting of a COVID-19 infection. The SARS-CoV-2 virus does not appear to cause a more severe metabolic deterioration than is typical.

Once in a Blue Moon, a Very Rare Coexistence of Glutaric Acidemia Type I and Mucopolysaccharidosis Type IIIB in a Patient

Background: Glutaric acidemia (GAI) and mucopolysaccharidosis type IIIB (MPSIIIB) are two rare genetic disorders caused by pathogenic variants in two different genes. Here, we report a coexistence of these two different rare disorders in an individual. Methods: A four-year-old Iranian boy born to first-cousin parents suspected to have MPSIIIB and/or GAI was investigated in this study. Targeted genomic enrichment and next-generation sequencing were used to examine genes related to MPS and GA. Sanger sequencing was performed to confirm the results. Results: Two homozygous likely pathogenic variants in α-N-acetylglucosaminidase (NAGLU) and GCDH genes were found and confirmed in the proband. Conclusion: A combination of specific features of two different diseases in a patient has been reported here. More studies on this case and similar cases can provide more information about the effect of simultaneous pathogenic variants in different genes.

Elevated levels of BDNF and cathepsin-d as possible peripheral markers of neurodegeneration in plasma of patients with glutaric acidemia type I.

Glutaric acidemia type I (GA1) is caused by severe deficiency of glutaryl-CoA dehydrogenase activity, resulting in an accumulation of glutaric acid and glutarylcarnitine (C5DC) in the organism. Patients affected by GA1 are asymptomatic in the neonate period but usually manifest chronically progressive neurodegeneration apart from severe encephalopathic crises associated with acute striatum necrosis. Neurological manifestations like dyskinesia, dystonia, hypotonia, muscle stiffness, and spasticity are present. Treatment is based on protein/lysine restriction and l-carnitine supplementation. In this work, we evaluated markers of neurodegeneration and inflammation, namely BDNF (brain-derived neurotrophic factor), NCAM (neuronal adhesion molecule), PDGF-AA (platelet-derived growth factor), and cathepsin-d in plasma of six treated GA1 patients. We first found marked increases of plasma C5DC concentrations in GA1 patients, as well as increased levels of the markers BDNF and cathepsin-d as compared to those of age-matched healthy children. Furthermore, C5DC concentrations were highly correlated with the levels of cathepsin-d. These results may demonstrate that brain tissue degeneration is present in GA1 patients and that there is a relationship between increased metabolites concentrations with this process. To the best of our knowledge, this is so far the first study showing altered peripheral parameters of neurodegeneration and inflammation in GA1 patients.

Cephalosporin-related neurotoxicity: Metabolic encephalopathy or non-convulsive status epilepticus?

Metabolic encephalopathy and Non-Convulsive Status Epilepticus (NCSE) have been reported with cephalosporin use, particularly cefepime. We aimed to analyze the clinical and EEG findings in patients with cephalosporin-related neurotoxicity (CRN) at our hospital identified via the hospital EEG database, and to critically review CRN case reports in the literature. A Medline search was performed to identify CRN cases where a representative sample of EEG was provided. EEGs were analyzed using published criteria differentiating NCSE from triphasic waves (TW). Eleven patients at our hospital were identified with CRN (9 cefepime, 2 ceftriaxone): all had an encephalopathy with decreased consciousness and/or confusion. One patient had clinical seizures and 6 had multifocal myoclonus. All patients had abnormal EEGs, all with moderate to severe generalized slowing and 10 also with TW. Recovery was related to cephalosporin withdrawal rather than antiepileptic therapy. Analysis of 37 EEG samples of CRN patients reported in the literature as NCSE (30) or TW (7) revealed that most did not meet criteria for NCSE, with 33 showing TW, 1 showing generalised epileptiform discharges and 3 being uninterpretable. CRN usually produces a toxic encephalopathy rather than NCSE, and is commonly associated with triphasic waves on EEG. In most patients anti-epileptic and/or sedative drugs do not hasten clinical improvement.

MYORG is associated with recessive primary familial brain calcification.

Objective: To investigate the genetic basis of the recessive form of primary familial brain calcification and study pathways linking a novel gene with known dominant genes that cause the disease. Methods: Whole exome sequencing and Sanger-based segregation analysis were used to identify possible disease causing mutations. Mutation pathogenicity was validated by structural protein modeling. Functional associations between the candidate gene, MYORG, and genes previously implicated in the disease were examined through phylogenetic profiling. Results: We studied nine affected individuals from two unrelated families of Middle Eastern origin. The median age of symptom onset was 29.5 years (range 21-57 years) and dysarthria was the most common presenting symptom. We identified in the MYORG gene, a homozygous c.1233delC mutation in one family and c.1060_1062delGAC mutation in another. The first mutation results in protein truncation and the second in deletion of a highly conserved aspartic acid that is likely to disrupt binding of the protein with its substrate. Phylogenetic profiling analysis of the MYORG protein sequence suggests co-evolution with a number of calcium channels as well as other proteins related to regulation of anion transmembrane transport (False Discovery Rate, FDR < 10-8) and with PDCD6IP, a protein interacting with PDGFR ß which is known to be involved in the disease. Interpretation: MYORG mutations are linked to a recessive form of primary familial brain calcification. This association was recently described in patients of Chinese ancestry. We suggest the possibility that MYORG mutations lead to calcification in a PDGFR ß-related pathway.

Dyskinesia in a Child: A Concern for a Rare Neuro-Metabolic Disorder.

A 3-year child is discussed who presented with dyskinesia, large head size, developmental delay, and recurrent infections necessitating multiple hospital admissions. The diagnosis was not made at initial presentation or even after multiple hospital admissions. An organic acidemia was suspected, based on raised ammonia and lactate levels and metabolic acidosis and the diagnosis of glutaric aciduria Type 1 was established by finding markedly elevated levels of glutaric acid and its specific metabolites on urine organic acids analysis by gas chromatography-mass spectrometry, in the setting of specific clinical features. Further supporting evidence was provided by CT scan brain showing subdural hygroma along left cerebral hemisphere causing gyral flattening and widening of sylvian fissure.

Movement Disorders in Treatable Inborn Errors of Metabolism.

There are several hundred single-gene disorders that we classify as inborn errors of metabolism. Inborn errors of metabolism are often rare and highly heterogeneous multisystem diseases with non-neurological and neurological manifestations, commonly with onset during childhood. Movement disorders are among the most common neurological problems in inborn errors of metabolism, but, in many cases, remain poorly defined. Although movement disorders are usually not the only and often not the presenting symptom, their recognition can facilitate a diagnosis. Movement disorders contribute substantially to the morbidity in inborn errors of metabolism and can have a significant impact on quality of life. Common metabolic movement disorders include the monoamine neurotransmitter disorders, disorders of amino and organic acid metabolism, metal storage disorders, lysosomal storage disorders, congenital disorders of autophagy, disorders of creatine metabolism, vitamin-responsive disorders, and disorders of energy metabolism. Importantly, disease-modifying therapies exist for a number of inborn errors of metabolism, and early recognition and treatment can prevent irreversible CNS damage and reduce morbidity and mortality. A phenomenology-based approach, based on the predominant movement disorder, can facilitate a differential diagnosis and can guide biochemical, molecular, and imaging testing. The complexity of metabolic movement disorders demands an interdisciplinary approach and close collaboration of pediatric neurologists, neurologists, geneticists, and experts in metabolism. In this review, we develop a general framework for a phenomenology-based approach to movement disorders in inborn errors of metabolism and discuss an approach to identifying the "top ten" of treatable inborn errors of metabolism that present with movement disorders-diagnoses that should never be missed. © 2018 International Parkinson and Movement Disorder Society.