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Mitochondrial translation defects are a continuously growing group of disorders showing a large variety of clinical symptoms including a wide range of neurological abnormalities. To date, mutations in PTCD3, encoding a component of the mitochondrial ribosome, have only been reported in a single individual with clinical evidence of Leigh syndrome. Here, we describe three additional PTCD3 individuals from two unrelated families, broadening the genetic and phenotypic spectrum of this disorder, and provide definitive evidence that PTCD3 deficiency is associated with Leigh syndrome. The patients presented in the first months of life with psychomotor delay, respiratory insufficiency and feeding difficulties. The neurologic phenotype included dystonia, optic atrophy, nystagmus and tonic-clonic seizures. Brain MRI showed optic nerve atrophy and thalamic changes, consistent with Leigh syndrome. WES and RNA-seq identified compound heterozygous variants in PTCD3 in both families: c.[1453-1GC];[1918CG] and c.[710del];[902CT]. The functional consequences of the identified variants were determined by a comprehensive characterization of the mitochondrial function. PTCD3 protein levels were significantly reduced in patient fibroblasts and, consistent with a mitochondrial translation defect, a severe reduction in the steady state levels of complexes I and IV subunits was detected. Accordingly, the activity of these complexes was also low, and high-resolution respirometry showed a significant decrease in the mitochondrial respiratory capacity. Functional complementation studies demonstrated the pathogenic effect of the identified variants since the expression of wild-type PTCD3 in immortalized fibroblasts restored the steady-state levels of complexes I and IV subunits as well as the mitochondrial respiratory capacity. Additionally, minigene assays demonstrated that three of the identified variants were pathogenic by altering PTCD3 mRNA processing. The fourth variant was a frameshift leading to a truncated protein. In summary, we provide evidence of PTCD3 involvement in human disease confirming that PTCD3 deficiency is definitively associated with Leigh syndrome.

Glutamatergic neurotransmission is crucial for brain development, wiring neuronal function, and synaptic plasticity mechanisms. Recent genetic studies showed the existence of autosomal dominant de novo GRIN gene variants associated with GRIN-related disorders (GRDs), a rare pediatric neurological disorder caused by N-methyl- d-aspartate receptor (NMDAR) dysfunction. Notwithstanding, GRIN variants identification is exponentially growing and their clinical, genetic, and functional annotations remain highly fragmented, representing a bottleneck in GRD patient's stratification. To shorten the gap between GRIN variant identification and patient stratification, we present the GRIN database (GRINdb), a publicly available, nonredundant, updated, and curated database gathering all available genetic, functional, and clinical data from more than 4000 GRIN variants. The manually curated GRINdb outputs on a web server, allowing query and retrieval of reported GRIN variants, and thus representing a fast and reliable bioinformatics resource for molecular clinical advice. Furthermore, the comprehensive mapping of GRIN variants' genetic and clinical information along NMDAR structure revealed important differences in GRIN variants' pathogenicity and clinical phenotypes, shedding light on GRIN-specific fingerprints. Overall, the GRINdb and web server is a resource for molecular stratification of GRIN variants, delivering clinical and investigational insights into GRDs. GRINdb is accessible at http://lmc.uab.es/grindb.

Rett syndrome (RTT) is an early-onset neurodevelopmental disorder that almost exclusively affects girls and is totally disabling. Three genes have been identified that cause RTT: MECP2, CDKL5 and FOXG1. However, the etiology of some of RTT patients still remains unknown. Recently, next generation sequencing (NGS) has promoted genetic diagnoses because of the quickness and affordability of the method. To evaluate the usefulness of NGS in genetic diagnosis, we present the genetic study of RTT-like patients using different techniques based on this technology. We studied 1577 patients with RTT-like clinical diagnoses and reviewed patients who were previously studied and thought to have RTT genes by Sanger sequencing. Genetically, 477 of 1577 patients with a RTT-like suspicion have been diagnosed. Positive results were found in 30% by Sanger sequencing, 23% with a custom panel, 24% with a commercial panel and 32% with whole exome sequencing. A genetic study using NGS allows the study of a larger number of genes associated with RTT-like symptoms simultaneously, providing genetic study of a wider group of patients as well as significantly reducing the response time and cost of the study.

Recently, You, Hoover-Fong, and colleagues described a disease caused by a deficiency of the telomere maintenance 2 gene (We report two siblings, diagnosed with You-Hoover-Fong syndrome at the age of 28 and 14 months. Both were genetically studied to find the cause of their developmental delay and microcephaly.The identical compound heterozygous missense mutations in theWe report nuclear-lamellar cataracts in two siblings diagnosed with You-Hoover-Fong syndrome.

Background and ObjectivesGenetic white matter disorders (GWMD) are of heterogeneous origin, with >100 causal genes identified to date. Classic targeted approaches achieve a molecular diagnosis in only half of all patients. We aimed to determine the clinical utility of singleton whole-exome sequencing and whole-genome sequencing (sWES-WGS) interpreted with a phenotype- and interactome-driven prioritization algorithm to diagnose GWMD while identifying novel phenotypes and candidate genes.MethodsA case series of patients of all ages with undiagnosed GWMD despite extensive standard-of-care paraclinical studies were recruited between April 2017 and December 2019 in a collaborative study at the Bellvitge Biomedical Research Institute (IDIBELL) and neurology units of tertiary Spanish hospitals. We ran sWES and WGS and applied our interactome-prioritization algorithm based on the network expansion of a seed group of GWMD-related genes derived from the Human Phenotype Ontology terms of each patient.ResultsWe evaluated 126 patients (101 children and 25 adults) with ages ranging from 1 month to 74 years. We obtained a first molecular diagnosis by singleton WES in 59% of cases, which increased to 68% after annual reanalysis, and reached 72% after WGS was performed in 16 of the remaining negative cases. We identified variants in 57 different genes among 91 diagnosed cases, with the most frequent being RNASEH2B, EIF2B5, POLR3A, and PLP1, and a dual diagnosis underlying complex phenotypes in 6 families, underscoring the importance of genomic analysis to solve these cases. We discovered 9 candidate genes causing novel diseases and propose additional putative novel candidate genes for yet-to-be discovered GWMD.DiscussionOur strategy enables a high diagnostic yield and is a good alternative to trio WES/WGS for GWMD. It shortens the time to diagnosis compared to the classical targeted approach, thus optimizing appropriate management. Furthermore, the interactome-driven prioritization pipeline enables the discovery of novel disease-causing genes and phenotypes, and predicts novel putative candidate genes, shedding light on etiopathogenic mechanisms that are pivotal for myelin generation and maintenance.

Methyl-CpG-binding protein 2 (MeCP2) is an X-linked epigenetic modulator whose dosage is critical for neural development and function. Loss-of-function mutations in MECP2 cause Rett Syndrome (RTT, OMIM #312750) while duplications in the Xq28 locus containing MECP2 and Interleukin-1 receptor-associated kinase 1 (IRAK1) cause MECP2 duplication syndrome (MDS, OMIM #300260). Both are rare neurodevelopmental disorders that share clinical symptoms, including intellectual disability, loss of speech, hand stereotypies, vasomotor deficits and seizures. The main objective of this exploratory study is to identify novel signaling pathways and potential quantitative biomarkers that could aid early diagnosis and/or the monitoring of disease progression in clinical trials. We analyzed by RT-PCR gene expression in whole blood and microRNA (miRNA) expression in plasma, in a cohort of 20 females with Rett syndrome, 2 males with MECP2 duplication syndrome and 28 healthy controls, and correlated RNA expression with disease and clinical parameters. We have identified a set of potential biomarker panels for RTT diagnostic and disease stratification of patients with microcephaly and vasomotor deficits. Our study sets the basis for larger studies leading to the identification of specific miRNA signatures for early RTT detection, stratification, disease progression and segregation from other neurodevelopmental disorders. Nevertheless, these data will require verification and validation in further studies with larger sample size including a whole range of ages.

Background Following the broad application of new analytical methods, more and more pathophysiological processes in previously unknown diseases have been elucidated. The spectrum of clinical presentation of rare inherited metabolic diseases (IMDs) is broad and ranges from single organ involvement to multisystemic diseases. With the aim of overcoming the limited knowledge about the natural course, current diagnostic and therapeutic approaches, the project has established the first unified patient registry for IMDs that fully meets the requirements of the European Infrastructure for Rare Diseases (ERDRI). Results In collaboration with the European Reference Network for Rare Hereditary Metabolic Disorders (MetabERN), the Unified European registry for Inherited Metabolic Diseases (U-IMD) was established to collect patient data as an observational, non-interventional natural history study. Following the recommendations of the ERDRI the U-IMD registry uses common data elements to define the IMDs, report the clinical phenotype, describe the biochemical markers and to capture the drug treatment. Until today, more than 1100 IMD patients have been registered. Conclusion The U-IMD registry is the first observational, non-interventional patient registry that encompasses all known IMDs. Full semantic interoperability for other registries has been achieved, as demonstrated by the use of a minimum common core data set for equivalent description of metabolic patients in U-IMD and in the patient registry of the European Rare Kidney Disease Reference Network (ERKNet). In conclusion, the U-IMD registry will contribute to a better understanding of the long-term course of IMDs and improved patients care by understanding the natural disease course and by enabling an optimization of diagnostic and therapeutic strategies.

Background Mitochondrial diseases (MD) are genetic metabolic disorders that impair normal mitochondrial structure or function. The aim of this study was to investigate the status of circulating cell-free mitochondrial DNA (ccfmtDNA) in cerebrospinal fluid (CSF), together with other biomarkers (growth differentiation factor-15 [GDF-15], alanine, and lactate), in a cohort of 25 patients with a molecular diagnosis of MD. Methods Measurement of ccfmtDNA was performed by using droplet digital PCR. Results The mean copy number of ccfmtDNA was approximately 6 times higher in the MD cohort compared to the control group; patients with mitochondrial deletion and depletion syndromes (MDD) had the higher levels. We also detected the presence of both wild-type mtDNA and mtDNA deletions in CSF samples of patients with single deletions. Patients with MDD with single deletions had significantly higher concentrations of GDF-15 in CSF than controls, whereas patients with point mutations in mitochondrial DNA presented no statistically significant differences. Additionally, we found a significant positive correlation between ccfmtDNA levels and GDF-15 concentrations (r = 0.59, P = 0.016). Conclusion CSF ccfmtDNA levels are significantly higher in patients with MD in comparison to controls and, thus, they can be used as a novel biomarker for MD research. Our results could also be valuable to support the clinical outcome assessment of MD patients.

Background: The ATP7A gene encodes a copper transporter whose mutations cause Menkes disease, occipital horn syndrome (OHS), and, less frequently, ATP7A-related distal hereditary motor neuropathy (dHMN). Here we describe a family with OHS caused by a novel mutation in the ATP7A gene, including a patient with a comorbid dHMN that worsened markedly after being treated with copper histidinate. Methods: We studied in detail the clinical features of the patients and performed a genomic analysis by using TruSight One Expanded Sequencing Panel. Subsequently, we determined the ATP7A and ATP7B expression levels, mitochondrial membrane potential, and redox balance in cultured fibroblasts of Patient 1. Results: We found a novel ATP7A late truncated mutation p.Lys1412AsnfsX15 in the two affected members of this family. The co-occurrence of OHS and dHMN in Patient 1 reveals the variable phenotypic expressivity of the variant. A severe clinical and neurophysiologic worsening was observed in the dHMN of Patient 1 when he was treated with copper replacement therapy, with a subsequent fast recovery after the copper histidinate was withdrawn. Functional studies revealed that the patient had low levels of both ATP7A and ATP7B, the other copper transporter, and high levels of superoxide ion in the mitochondria. Conclusions: Our findings broaden the clinical spectrum of ATP7A-related disorders and demonstrate that two clinical phenotypes can occur in the same patient. The copper-induced toxicity and low levels of both ATP7A and ATP7B in our patient suggest that copper accumulation in motor neurons is the path-ogenic mechanism in ATP7A-related dHMN. (c) 2021 Elsevier Inc. All rights reserved.

De novo GRIN variants, encoding for the ionotropic glutamate NMDA receptor subunits, have been recently associated with GRIN-related disorders, a group of rare paediatric encephalopathies. Current investigational and clinical efforts are focused to functionally stratify GRIN variants, towards precision therapies of this primary disturbance of glutamatergic transmission that affects neuronal function and brain. In the present study, we aimed to comprehensively delineate the functional outcomes and clinical phenotypes of GRIN protein truncating variants (PTVs)—accounting for ~20% of disease-associated GRIN variants—hypothetically provoking NMDAR hypofunctionality. To tackle this question, we created a comprehensive GRIN PTVs variants database compiling a cohort of nine individuals harbouring GRIN PTVs, together with previously identified variants, to build-up an extensive GRIN PTVs repertoire composed of 293 unique variants. Genotype–phenotype correlation studies were conducted, followed by cell-based assays of selected paradigmatic GRIN PTVs and their functional annotation. Genetic and clinical phenotypes meta-analysis revealed that heterozygous GRIN1, GRIN2C, GRIN2D, GRIN3A and GRIN3B PTVs are non-pathogenic. In contrast, heterozygous GRIN2A and GRIN2B PTVs are associated with specific neurological clinical phenotypes in a subunit- and domain-dependent manner. Mechanistically, cell-based assays showed that paradigmatic pathogenic GRIN2A and GRIN2B PTVs result on a decrease of NMDAR surface expression and NMDAR-mediated currents, ultimately leading to NMDAR functional haploinsufficiency. Overall, these findings contribute to delineate GRIN PTVs genotype–phenotype association and GRIN variants stratification. Functional studies showed that GRIN2A and GRIN2B pathogenic PTVs trigger NMDAR hypofunctionality, and thus accelerate therapeutic decisions for this neurodevelopmental condition., ISCIII, cofunded by European Regional Development Fund (ERDF), a way to build Europe (grants PI19/00348 and PI16/00851); Miguel Servet Program (CPII16/00021, ISCIII) and Serra Húnter Fellow to X.A.; SAF2016-77830-R to M.O.; European Regional development Fund (ERDF)-Ministerio de Ciencia e Innovación (grant BFU2017-83317-P) and Ministerio de Ciencia e Innovación-María de Maeztu (MDM-2017-0729) to D.S. and PI18/00111 [ISCIII, cofunded by European Regional Development Fund (ERDF), a way to build Europe] to À.G.-C. and N.J.-P.; Fundación Tatiana Pérez de Guzmán el Bueno PhD fellowship to A.S.-G.; crowdfunding initiative Precipita (FECYT) to F.M.

Following an uneventful pregnancy, a boy was born from nonconsanguineous parents with no relevant family history. Within the first 24 hours after birth, he presented with cyanosis, lethargy, decreased spontaneous movements, hyperexcitability, and mild hypotonia. Under the suspicion of a mitochondrial disorder (MD), supplementation with different enzymatic cofactors was started, with no improvement. Refractory epilepsy, psychomotor delay, nystagmoid movements, and non-nephrotic range proteinuria were observed. The patient died at 9 months of age. Venous blood analysis showed lactic acidosis. Lactate was also increased in cerebrospinal fluid (CSF): 3.74 mmol/L (reference interval [RI]: 1.11–2.22 mmol/L)). Impaired mitochondrial metabolism was further suggested by an increase of plasma alanine (797 µmol/L, RI: 190–337 µmol/L), CSF alanine (81 µmol/L, RI: 12–52 µmol/L) and an abnormal urine organic acid profile (increased excretion of succinate, fumarate, and 2-oxoglutarate). Increased concentrations of fibroblast growth factor-21 (FGF-21) (952 ng/L, RI: 0–300 ng/L) were detected. Analysis of coenzyme Q10 (CoQ) by HPLC-electrochemical detection gave normal results in plasma, while a decrease in fibroblasts (36 nmol/g protein, RI: 91–151 nmol/g protein) and skeletal muscle was observed (56.2 nmol/g protein, RI: 110–480 nmol/g protein) (Fig. 1). The activity of mitochondrial respiratory chain (MRC) succinate-cytochrome c reductase in fibroblasts, which depends on CoQ status, was reduced (9.04 nmol/min/mg protein) when compared with a control line of neonatal fibroblasts analyzed in parallel (16.01 nmol/min/mg protein)., This work was supported by grants from the Instituto de Salud Carlos III (ISCIII-FIS PI17/00109 and PI17/01286). A.J. Paredes-Fuentes, a grant from the Instituto de Salud Carlos III (FI18/00253).

Rett syndrome, a serious neurodevelopmental disorder, has been associated with an altered expression of different synaptic-related proteins and aberrant glutamatergic and &gamma, aminobutyric acid (GABA)ergic neurotransmission. Despite its severity, it lacks a therapeutic option. Through this work we aimed to define the relationship between MeCP2 and GABAA.-A1 receptor expression, emphasizing the time dependence of such relationship. For this, we analyzed the expression of the ionotropic receptor subunit in different MeCP2 gene-dosage and developmental conditions, in cells lines, and in primary cultured neurons, as well as in different developmental stages of a Rett mouse model. Further, RNAseq and systems biology analysis was performed from post-mortem brain biopsies of Rett patients. We observed that the modulation of the MeCP2 expression in cellular models (both Neuro2a (N2A) cells and primary neuronal cultures) revealed a MeCP2 positive effect on the GABAA.-A1 receptor subunit expression, which did not occur in other proteins such as KCC2 (Potassium-chloride channel, member 5). In the Mecp2+/&minus, mouse brain, both the KCC2 and GABA subunits expression were developmentally regulated, with a decreased expression during the pre-symptomatic stage, while the expression was variable in the adult symptomatic mice. Finally, the expression of the gamma-aminobutyric acid (GABA) receptor-related synaptic proteins from the postmortem brain biopsies of two Rett patients was evaluated, specifically revealing the GABA A1R subunit overexpression. The identification of the molecular changes along with the Rett syndrome prodromic stages strongly endorses the importance of time frame when addressing this disease, supporting the need for a neurotransmission-targeted early therapeutic intervention.

The elevation of neopterin in cerebrospinal fluid (CSF) has been reported in several neuroinflammatory disorders. However, it is not expected that neopterin alone can discriminate among different neuroinflammatory etiologies. We conducted an observational retrospective and case–control study to analyze the CSF biomarkers neopterin, total proteins, and leukocytes in a large cohort of pediatric patients with neuroinflammatory disorders. CSF samples from 277 subjects were included and classified into four groups: Viral meningoencephalitis, bacterial meningitis, acquired immune-mediated disorders, and patients with no-immune diseases (control group). CSF neopterin was analyzed with high-performance liquid chromatography. Microbiological diagnosis included bacterial CSF cultures and several specific real-time polymerase chain reactions. Molecular testing for multiple respiratory pathogens was also included. Antibodies against neuronal and glial proteins were tested. Canonical discriminant analysis of the three biomarkers was conducted to establish the best discriminant functions for the classification of the different clinical groups. Model validation was done by biomarker analyses in a new cohort of 95 pediatric patients. CSF neopterin displayed the highest values in the viral and bacterial infection groups. By applying canonical discriminant analysis, it was possible to classify the patients into the different groups. Validation analyses displayed good results for neuropediatric patients with no-immune diseases and for viral meningitis patients, followed by the other groups. This study provides initial evidence of a more efficient approach to promote the timely classification of patients with viral and bacterial infections and acquired autoimmune disorders. Through canonical equations, we have validated a new tool that aids in the early and differential diagnosis of these neuroinflammatory conditions.

Inborn errors of metabolism cause a wide spectrum of neurodevelopmental and neurodegenerative conditions [15]. A pivotal enzyme located at the intersection of the amino acid and folic acid metabolic pathways is SHMT2, the mitochondrial form of serine hydroxymethyltransferase. SHMT2 performs the first step in a series of reactions that provide one-carbon units covalently bound to folate species in mitochondria: it transfers one-carbon units from serine to tetrahydrofolate (THF), generating glycine and 5,10-methylene-THF. Using whole exome sequencing (WES), we identified biallelic SHMT2 variants in five individuals from four different families. All identified variants were located in conserved residues, either absent or extremely rare in control databases (gnomAD, ExAC), and cosegregated based on a recessive mode of inheritance (pRec = 0.9918 for this gene). In family F1, a homozygous missense variant present in two affected siblings was located in a region without heterozygosity (~ 10 Mb, the only region > 1 Mb shared by both siblings) in which no other candidate variants were found, providing a strong genetic evidence of causality for these variants. The missense/in-frame deletion nature of these variants, and the absence of loss-of-function homozygous individuals in control databases, combined with the fact that complete loss of SHMT2 is embryonic lethal in the mouse, suggested that these variants may cause hypomorphic effects. Using 3D molecular dynamics models of the SHMT2 protein, we concluded that these candidate variants probably alter the SHMT2 oligomerization process, and/or disrupt the conformation of the active site, thus inducing deleterious effects on SHMT2 enzymatic function.

To date, inborn errors of neurotransmitters have been defined based on the classic concept of inborn error of metabolism (IEM), and they include defects in synthesis, catabolism, and transport pathways. However, the omics era is bringing insights into new diseases and is leading to an extended definition of IEM including new categories and mechanisms. Neurotransmission takes place at the synapse, the most specialized tight junction in the brain. The concept of "synaptic metabolism" would point to the specific chemical composition and metabolic functions of the synapse. Based on these specialized functions, we aim to provide a tentative overview about the major categories of IEM susceptible to affect neurotransmission. Small molecule defects (biogenic amines and amino acids) and energy defects are amongst the most prevalent diseases reported to disturb the concentration of CSF neurotransmitters. In these IEM, the neurological phenotypes have been largely described. Disorders of complex molecules are not typically considered as diseases affecting neurotransmission. However, most of them have been recently discovered and are involved in intracellular vesiculation, trafficking, processing, and quality control mechanisms. In this large group, neurotransmission is affected in disorders of chaperones and autophagy, disorders of the synaptic vesicle, and diseases affecting pre-synaptic membranes (synthesis and remodeling of complex lipids, defects of glycosylation). Disorders of the vesicle pools, receptor trafficking, and the chronobiology of neurotransmission are potentially emerging new categories. Finally, although not considered as IEM, channelopathies are a large group of diseases disturbing neurotransmitter homeostasis. New CSF biomarkers will probably contribute to improve the diagnosis of these disorders and find new therapeutic targets.

It has become increasingly evident that inborn errors of metabolism (IEMs) are particularly prevalent as diseases of the nervous system and that a broader, more inclusive definition of IEM is necessary. In fact, as long as biochemistry is involved, any kind of monogenic disease can become an IEM. This new, extended definition includes new categories and mechanisms, and as a general trend will go beyond a single biochemical pathway and/or organelle, and will appear as a connection of multiple crossroads in a system biology approach. From one side, a simplified and updated classification of IEM is presented that mixes elements from the diagnostic approach with pathophysiological considerations into three large categories based on the size of molecules (“small and simple” or “large and complex”) and their implication in energy metabolism. But from another side, whatever their size, metabolites involved in IEM may behave in the brain as signalling molecules, structural components and fuels, and many metabolites have more than one role. Neurometabolism is becoming more relevant, not only in relation to these new categories of diseases but also as a necessary way to explain the mechanisms of brain damage in classically defined categories of IEM. Brain metabolism, which has been largely disregarded in the traditional approach to investigating and treating neurological diseases, is a major clue and probably the next imminent “revolution” in neurology and neuroscience. Biochemistry (metabolism) and cell neurobiology need to meet. Additionally, the brain should be studied as a system (connecting different levels of complexity). Electronic supplementary material The online version of this article (10.1007/s10545-018-0226-8) contains supplementary material, which is available to authorized users.

The specialty of inherited metabolic disease is at the forefront of progress in medicine, with new methods in metabolomics and genomics identifying the molecular basis for a growing number of conditions and syndromes. This review presents an updated pathophysiologic classification of inborn errors of metabolism and a method of clinical screening in neonates, late-onset emergencies, neurologic deterioration, and other common clinical scenarios. When and how to investigate a metabolic disorder is presented to encourage physicians to use sophisticated biochemical investigations and not miss a treatable disorder.

Aim Gamma-aminobutyric acid (GABA) is a major modulator in brain maturation and its role in many different neurodevelopmental disorders has been widely reported. Although the involvement of GABA in different disorders has been related to its regulatory function as an inhibitory neurotransmitter in the mature brain, co-transmitter, and signalling molecule, little is known about its role as a clinical biomarker in neuropaediatric disorders. The aim of this study is to report the cerebrospinal fluid (CSF) free-GABA concentrations in a large cohort of patients (n=85) with different neurological disorders. Method GABA was measured in the CSF of neuropaediatric patients using capillary electrophoresis with laser-induced fluorescence detection. Other neurotransmitters (amino acids and monoamines) were also analysed. Results GABA concentrations in CSF were abnormal, with a greater frequency (44%) than monoamines (20%) in neuropaediatric patients compared with our reference values. Although we included a few patients with inborn errors of metabolism, GABA levels in CSF were more frequently abnormal in metabolic disorders than in other nosological groups. Interpretation Our work suggests further research into brain GABAergic status in neuropaediatric disorders, which could also lead to new therapeutic strategies. What this paper adds Homeostasis of GABA seems more vulnerable than that of monoamines in the developing brain. The highest GABA levels are found in the primary GABA neurotransmitter disorder SSADH deficiency. GABA alterations are not specific for any clinical or neuroimaging presentation.

Background: GRIN-related disorders (GRD), the so-called grinpathies, is a group of rare encephalopathies caused by mutations affecting GRIN genes (mostly GRIN1, GRIN2A and GRIN2B genes), which encode for the GluN subunit of the N-methyl D-aspartate (NMDA) type ionotropic glutamate receptors. A growing number of functional studies indicate that GRIN-encoded GluN1 subunit disturbances can be dichotomically classified into gain- and loss-of-function, although intermediate complex scenarios are often present. Methods: In this study, we aimed to delineate the structural and functional alterations of GRIN1 disease-associated variants, and their correlations with clinical symptoms in a Spanish cohort of 15 paediatric encephalopathy patients harbouring these variants. Results: Patients harbouring GRIN1 disease-associated variants have been clinically deeply-phenotyped. Further, using computational and in vitro approaches, we identified different critical checkpoints affecting GluN1 biogenesis (protein stability, subunit assembly and surface trafficking) and/or NMDAR biophysical properties, and their association with GRD clinical symptoms. Conclusions: Our findings show a strong correlation between GRIN1 variants-associated structural and functional outcomes. This structural-functional stratification provides relevant insights of genotype-phenotype association, contributing to future precision medicine of GRIN1-related encephalopathies.

The presence of monoamines and their cofactors (the pterins and vitamin B6 (pyridoxal phosphate (PLP))) in human cerebrospinal fluid (CSF) can be used as indicators of the biosynthesis and turnover of dopamine and serotonin in the brain. In addition, abnormalities in the CSF levels of these molecules are associated with various neurological diseases, including genetic diseases leading to dopamine and serotonin deficiency. Here, we provide a set of quantitative high-performance liquid-chromatography (HPLC) approaches to determine CSF levels of monoamines and their cofactors. This protocol describes step-by-step procedures for CSF sample preparation for the analysis of different molecules, HPLC calibration and analysis, and data quantification and interpretation. Unlike plasma/tissue/blood samples, CSF requires minimal sample preparation: in this protocol, only the analysis of PLP requires mixing with trichloroacetic acid to release the protein-bound vitamin, centrifugation, and mixing of the supernatant with phosphate buffer and sodium cyanide for derivatization in alkaline conditions. Monoamines are analyzed by HPLC with coulometric electrochemical detection (ED), pterins are analyzed by HPLC with coupled coulometric electrochemical and fluorescence detection, and PLP is analyzed by HPLC with fluorescence detection. The quantification of all compounds is achieved by external calibration procedures, and internal quality control and standards are analyzed in each run. We anticipate that investigation of dopamine and serotonin disturbances will be facilitated by measurements of these compounds in human CSF and other biological samples. The estimated time for the different procedures primarily depends on the electrochemical detector stabilization. Overnight stabilization of this detector is advised, and, after that step, preanalytical equilibration rarely exceeds 3 h.

Rett syndrome, a serious neurodevelopmental disorder, has been associated with an altered expression of different synaptic-related proteins and aberrant glutamatergic and γ-aminobutyric acid (GABA)ergic neurotransmission. Despite its severity, it lacks a therapeutic option. Through this work we aimed to define the relationship between MeCP2 and GABAA.-A1 receptor expression, emphasizing the time dependence of such relationship. For this, we analyzed the expression of the ionotropic receptor subunit in different MeCP2 gene-dosage and developmental conditions, in cells lines, and in primary cultured neurons, as well as in different developmental stages of a Rett mouse model. Further, RNAseq and systems biology analysis was performed from post-mortem brain biopsies of Rett patients. We observed that the modulation of the MeCP2 expression in cellular models (both Neuro2a (N2A) cells and primary neuronal cultures) revealed a MeCP2 positive effect on the GABAA.-A1 receptor subunit expression, which did not occur in other proteins such as KCC2 (Potassium-chloride channel, member 5). In the Mecp2+/− mouse brain, both the KCC2 and GABA subunits expression were developmentally regulated, with a decreased expression during the pre-symptomatic stage, while the expression was variable in the adult symptomatic mice. Finally, the expression of the gamma-aminobutyric acid (GABA) receptor-related synaptic proteins from the postmortem brain biopsies of two Rett patients was evaluated, specifically revealing the GABA A1R subunit overexpression. The identification of the molecular changes along with the Rett syndrome prodromic stages strongly endorses the importance of time frame when addressing this disease, supporting the need for a neurotransmission-targeted early therapeutic intervention.

Background Cerebrospinal fluid (CSF) metabolomic investigations are a powerful tool for studying neurometabolic diseases. We aimed to assess the effect of CSF contamination with blood on the concentrations of selected biomarkers. Methods CSF samples were spiked in duplicate with increasing volumes of whole blood under two conditions: (A) pooled CSF spiked with fresh whole blood and frozen to cause red blood cell (RBC) lysis; (B) pooled CSF spiked with fresh blood and centrifuged (the supernatant with no RBCs was frozen until the moment of analysis). CSF concentrations of amino acids, biogenic amines, pterins, and vitamins were analysed by HPLC coupled with tandem mass spectrometry, electrochemical and fluorescence detection. Results Aspartate, glutamate, taurine, ornithine, glycine, citrulline, pyridoxal 5´-phosphate, 5-methyltetrahydrofolate, and thiamine showed higher values when RBCs were lysed when compared with those of CSF with no RBC, while arginine, 5-hydroxyindoleacetic and homovanillic acids showed lower values. When RBCs were removed from CSF, only some amino acids, thiamine and pyridoxal 5´-phosphate showed moderately higher values when compared with the non-spiked CSF sample. Conclusions CSF-targeted metabolomic analysis is feasible even when substantial RBC contamination of CSF has occurred since CSF centrifugation to remove RBC prior to freezing eliminated most of the interferences observed.

BACKGROUND Laboratory investigations of cerebrospinal fluid (CSF) are essential when suspecting an inborn error of metabolism (IEM) involving neurological features. Available tests are currently performed on different analytical platforms, requiring a large sample volume and long turnaround time, which often delays timely diagnosis. Therefore, it would be preferable to have an "one-instrument" targeted multi-metabolite approach. METHOD A liquid chromatography-tandem mass spectrometry (LC-MS/MS) platform, based on two different methods for analysing 38 metabolites using positive and negative electrospray ionisation modes, was established. To allow for platform extension, both methods were designed to use the same CSF sample preparation procedure and to be run on the same separation column (ACE C18-PFP). RESULTS Assessment of the LC-MS/MS platform methods was first made by analytical validation, followed by the establishment of literature-based CSF cut-off values and reference ranges, and by the measurement of available samples obtained from patients with confirmed diagnoses of aromatic l-amino acid decarboxylase deficiency, guanidinoacetate methyltransferase deficiency, ornithine aminotransferase deficiency, cerebral folate deficiency and methylenetetrahydrofolate reductase deficiency. CONCLUSION An extendable targeted LC-MS/MS platform was developed for the analysis of multiple metabolites in CSF, thereby distinguishing samples from patients with IEM from non-IEM samples. Reference concentrations for several biomarkers in CSF are provided for the first time. By measurement on a single analytical platform, less sample volume is required (200 μL), diagnostic results are obtained faster, and preanalytical issues are reduced. SYNOPSIS LC-MS/MS platform for CSF analysis consisting of two differentially designed methods.

Encephalomyopathic mitochondrial DNA (mtDNA) depletion syndrome 13 (MTDPS13) is a rare genetic disorder caused by defects in F-box leucine-rich repeat protein 4 (FBXL4). Although FBXL4 is essential for the bioenergetic homeostasis of the cell, the precise role of the protein remains unknown. In this study, we report two cases of unrelated patients presenting in the neonatal period with hyperlactacidemia and generalized hypotonia. Severe mtDNA depletion was detected in muscle biopsy in both patients. Genetic analysis showed one patient as having in compound heterozygosis a splice site variant c.858+5G>C and a missense variant c.1510T>C (p.Cys504Arg) in FBXL4. The second patient harbored a frameshift novel variant c.851delC (p.Pro284LeufsTer7) in homozygosis. To validate the pathogenicity of these variants, molecular and biochemical analyses were performed using skin-derived fibroblasts. We observed that the mtDNA depletion was less severe in fibroblasts than in muscle. Interestingly, the cells harboring a nonsense variant in homozygosis showed normal mtDNA copy number. Both patient fibroblasts, however, demonstrated reduced mitochondrial transcript quantity leading to diminished steady state levels of respiratory complex subunits, decreased respiratory complex IV (CIV) activity, and finally, low mitochondrial ATP levels. Both patients also revealed citrate synthase deficiency. Genetic complementation assays established that the deficient phenotype was rescued by the canonical version of FBXL4, confirming the pathological nature of the variants. Further analysis of fibroblasts allowed to establish that increased mitochondrial mass, mitochondrial fragmentation, and augmented autophagy are associated with FBXL4 deficiency in cells, but are probably secondary to a primary metabolic defect affecting oxidative phosphorylation.

International audience; Autosomal dominant mutations in GRIN2B are associated with severe encephalopathy, but little is known about the pathophysiological outcomes and any potential therapeutic interventions. Genetic studies have described the association between de novo mutations of genes encoding the subunits of the N-methyl-D-aspartate receptor (NMDAR) and severe neurological conditions. Here, we evaluated a missense mutation in GRIN2B, causing a proline-to-threonine switch (P553T) in the GIuN2B subunit of NMDAR, which was found in a 5-year-old patient with Rett-like syndrome with severe encephalopathy. Structural molecular modeling predicted a reduced pore size of the mutant GIuN2B-containing NMDAR5. Electrophysiological recordings in a HEK-293T cell line expressing the mutated subunit confirmed this prediction and showed an associated reduced glutamate affinity. Moreover, GluN2B(P553T)-expressing primary murine hippocampal neurons showed decreased spine density, concomitant with reduced NMDA-evoked currents and impaired NMDAR-dependent insertion of the AMPA receptor subunit GluA1 at stimulated synapses. Furthermore, the naturally occurring coagonist D-serine restored function to GluN2B(P553T)-containing NMDAR5. L-Serine dietary supplementation of the patient was hence initiated, resulting in the increased abundance of D-serine in the plasma and brain. The patient has shown notable improvements in motor and cognitive performance and communication after 11 and 17 months of L-serine dietary supplementation. Our data suggest that L-serine supplementation might ameliorate GRIN2B-related severe encephalopathy and other neurological conditions caused by glutamatergic signaling deficiency.

A 3-year-old girl presented with severe epilepsy in the context of Borrelia infection. After ceftriaxone/lidocaine administration, she showed secondarily generalized focal crises that led to neurological and motor sequelae. Genetic studies identified in the patient two heterozygous POLG mutations (c.2591A>G; p.Asn864Ser and c.3649G>C; p.Ala1217Pro). Through analysis of POLG activity in cultured fibroblasts, we confirmed that the mutations altered the mtDNA turnover. Moreover, patient fibroblasts were more sensitive than controls in the presence of a mitochondrial replication-affecting drug, the antiretroviral azidothymidine. To test if ceftriaxone treatment could worsen the deleterious effect of the patient mutations, toxicity assays were performed. Cell toxicity, without direct effect on mitochondrial respiratory function, was detected at different antibiotic concentrations. The clinical outcome, together with the different in vitro sensitivity to ceftriaxone among patient and control cells, suggested that the mitochondrial disease symptoms were hastened by the infection and were possibly worsened by the pharmacological treatment. This study underscores the benefit of early genetic diagnosis of the patients with mitochondrial diseases, since they may be a target group of patients especially vulnerable to environmental factors.

Figure S2. Distribution of presenting symptoms of homocystinuria during the study. Cbl, cobalamin; CBS, cystathionine β-synthase; MRI, magnetic resonance imaging; MTHFR, 5, 10-methylenetetrahydrofolate reductase. (DOCX 15 kb)

© The Author(s) 2019., Identifying diseases displaying chronic low plasma Coenzyme Q10 (CoQ) values may be important to prevent possible cardiovascular dysfunction. The aim of this study was to retrospectively evaluate plasma CoQ concentrations in a large cohort of pediatric and young adult patients. We evaluated plasma CoQ values in 597 individuals (age range 1 month to 43 years, average 11 years), studied during the period 2005–2016. Patients were classified into 6 different groups: control group of healthy participants, phenylketonuric patients (PKU), patients with mucopolysaccharidoses (MPS), patients with other inborn errors of metabolism (IEM), patients with neurogenetic diseases, and individuals with neurological diseases with no genetic diagnosis. Plasma total CoQ was measured by reverse-phase high-performance liquid chromatography with electrochemical detection and ultraviolet detection at 275 nm. ANOVA with Bonferroni correction showed that plasma CoQ values were significantly lower in the PKU and MPS groups than in controls and neurological patients. The IEM group showed intermediate values that were not significantly different from those of the controls. In PKU patients, the Chi-Square test showed a significant association between having low plasma CoQ values and being classic PKU patients. The percentage of neurogenetic and other neurological patients with low CoQ values was low (below 8%). In conclusión, plasma CoQ monitoring in selected groups of patients with different IEM (especially in PKU and MPS patients, but also in IEM under protein-restricted diets) seems advisable to prevent the possibility of a chronic blood CoQ suboptimal status in such groups of patients., This work was supported by grant from the Instituto de Salud Carlos III (ISCIII-FIS PI17/00109, PI17/00021, PI17/01286, PI15/00166 and PI15/01082), the FEDER Funding Program from the European Union, CIBERER-ISCIII and Departamento de Ciencia, Tecnología y Universidad del Gobierno de Aragón (Grupos de Referencia B33_17R).

© 2020 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/), Rett syndrome (RTT; OMIM#312750) is mainly caused by mutations in the X-linked MECP2 gene (methyl-CpG-binding protein 2 gene; OMIM*300005), which leads to impairments in the brain-derived neurotrophic factor (BDNF) signalling. The boost of BDNF mediated effects would be a significant breakthrough but it has been hampered by the difficulty to administer BDNF to the central nervous system. Adenosine, an endogenous neuromodulator, may accomplish that role since through A2AR it potentiates BDNF synaptic actions in healthy animals. We thus characterized several hallmarks of the adenosinergic and BDNF signalling in RTT and explored whether A2AR activation could boost BDNF actions. For this study, the RTT animal model, the Mecp2 knockout (Mecp2-/y) (B6.129P2 (C)-Mecp2tm1.1Bird/J) mouse was used. Whenever possible, parallel data was also obtained from post-mortem brain samples from one RTT patient. Ex vivo extracellular recordings of field excitatory post-synaptic potentials in CA1 hippocampal area were performed to evaluate synaptic transmission and long-term potentiation (LTP). RT-PCR was used to assess mRNA levels and Western Blot or radioligand binding assays were performed to evaluate protein levels. Changes in cortical and hippocampal adenosine content were assessed by liquid chromatography with diode array detection (LC/DAD). Hippocampal ex vivo experiments revealed that the facilitatory actions of BDNF upon LTP is absent in Mecp2-/y mice and that TrkB full-length (TrkB-FL) receptor levels are significantly decreased. Extracts of the hippocampus and cortex of Mecp2-/y mice revealed less adenosine amount as well as less A2AR protein levels when compared to WT littermates, which may partially explain the deficits in adenosinergic tonus in these animals. Remarkably, the lack of BDNF effect on hippocampal LTP in Mecp2-/y mice was overcome by selective activation of A2AR with CGS21680. Overall, in Mecp2-/y mice there is an impairment on adenosinergic system and BDNF signalling. These findings set the stage for adenosine-based pharmacological therapeutic strategies for RTT, highlighting A2AR as a therapeutic target in this devastating pathology., The work was supported by a joint research grant awarded to TMR from Fundação Calouste Gulbenkian and FMUL (20130002/PEC/BG); Fundação para a Ciência e Tecnologia (FCT, AdoRett – LISBOA-01-0145-FEDER-031929/2017 and FCT SFRH/BD/118238/2016 granted to CML); Universidade de Lisboa (grant awarded by CML BD2015); the Association Française du Syndrome de Rett; Program “Educação pela Ciência” Bolsas CHLN/FMUL – GAPIC (Project No. 20190017); Twinning action (SynaNet) from the EU H2020 Programme; and the UID/BIM/50005/2019, project financed by the FCT/Ministério da Ciência, Tecnologia e Ensino Superior (MCTES), through the Fundos do Orçamento de Estado. The work performed at ICBAS/MedInUP by PCS and TMC was partially supported by FCT (FEDER funding, project UID/BIM/4308/2019 and UIDP/04308/2020).

Identifying diseases displaying chronic low plasma Coenzyme Q10 (CoQ) values may be important to prevent possible cardiovascular dysfunction. The aim of this study was to retrospectively evaluate plasma CoQ concentrations in a large cohort of pediatric and young adult patients. We evaluated plasma CoQ values in 597 individuals (age range 1 month to 43 years, average 11 years), studied during the period 2005–2016. Patients were classified into 6 different groups: control group of healthy participants, phenylketonuric patients (PKU), patients with mucopolysaccharidoses (MPS), patients with other inborn errors of metabolism (IEM), patients with neurogenetic diseases, and individuals with neurological diseases with no genetic diagnosis. Plasma total CoQ was measured by reverse-phase high-performance liquid chromatography with electrochemical detection and ultraviolet detection at 275 nm. ANOVA with Bonferroni correction showed that plasma CoQ values were significantly lower in the PKU and MPS groups than in controls and neurological patients. The IEM group showed intermediate values that were not significantly different from those of the controls. In PKU patients, the Chi-Square test showed a significant association between having low plasma CoQ values and being classic PKU patients. The percentage of neurogenetic and other neurological patients with low CoQ values was low (below 8%). In conclusión, plasma CoQ monitoring in selected groups of patients with different IEM (especially in PKU and MPS patients, but also in IEM under protein-restricted diets) seems advisable to prevent the possibility of a chronic blood CoQ suboptimal status in such groups of patients.

Mitochondrial diseases are a group of genetic disorders leading to the dysfunction of mitochondrial energy metabolism pathways. We aimed to assess the clinical phenotype and the biochemical cerebrospinal fluid (CSF) biogenic amine profiles of patients with different diagnoses of genetic mitochondrial diseases. We recruited 29 patients with genetically confirmed mitochondrial diseases harboring mutations in either nuclear or mitochondrial DNA (mtDNA) genes. Signs and symptoms of impaired neurotransmission and neuroradiological data were recorded. CSF monoamines, pterins, and 5-methyltetrahydrofolate (5MTHF) concentrations were analyzed using high-performance liquid chromatography with electrochemical and fluorescence detection procedures. The mtDNA mutations were studied by Sanger sequencing, Southern blot, and real-time PCR, and nuclear DNA was assessed either by Sanger or next-generation sequencing. Five out of 29 cases showed predominant dopaminergic signs not attributable to basal ganglia involvement, harboring mutations in different nuclear genes. A chi-square test showed a statistically significant association between high homovanillic acid (HVA) values and low CSF 5-MTHF values (chi-square = 10.916; p = 0.001). Seven out of the eight patients with high CSF HVA values showed cerebral folate deficiency. Five of them harbored mtDNA deletions associated with Kearns-Sayre syndrome (KSS), one had a mitochondrial point mutation at the mtDNA ATPase6 gene, and one had a POLG mutation. In conclusion, dopamine deficiency clinical signs were present in some patients with mitochondrial diseases with different genetic backgrounds. High CSF HVA values, together with a severe cerebral folate deficiency, were observed in KSS patients and in other mtDNA mutation syndromes.

The aim of this report is to present a tentative clinical and pathophysiological approach to diseases affecting the neuronal presynaptic terminal, with a major focus on synaptic vesicles (SVs). Diseases are classified depending on which step of the neurobiology of the SV is predominantly affected: (1) biogenesis of vesicle precursors in the neuronal soma; (2) transport along the axon; (3) vesicle cycle at the presynaptic terminal (exocytosis-endocytosis cycle, with the main purpose of neurotransmitter release). Given that SVs have been defined as individual organelles, we highlight the link between the biological processes disturbed by genetic mutations and the clinical presentation of these disorders. The great majority of diseases may present as epileptic encephalopathies, intellectual disability (syndromic or nonsyndromic) with/without autism spectrum disorder (and other neuropsychiatric symptoms), and movement disorders. These symptoms may overlap and present in patients as a combination of clinical signs that results in the spectrum of the synaptopathies. A small number of diseases may also exhibit neuromuscular signs. In general, SV disorders tend to be severe, early encephalopathies that interfere with neurodevelopment. As a consequence, developmental delay and intellectual disability are constant in almost all the defects described. Considering that some of these diseases might mimic other neurometabolic conditions (and in particular treatable disorders), an initial extensive metabolic workup should always be considered. Further knowledge into pathophysiological mechanisms and biomarkers, as well as descriptions of new presynaptic disorders, will probably take place in the near future.

Objective The mechanisms of the ketogenic diet remain unclear, but several predictors of response have been proposed. We aimed is to study the relationship between the etiology of epilepsy, cerebrospinal fluid neurotransmitters, pterins, and amino acids, and response to a ketogenic diet. Methods We studied 60 patients who began classic ketogenic diet treatment for refractory epilepsy. In 24 of 60 individuals, we analyzed cerebrospinal fluid neurotransmitters, pterins, and amino acids in baseline conditions. Mean age at epilepsy onset was 24 months, 83.3% were focal epilepsies, and in 51.7% the etiology of the epilepsy was unknown. Results Six months after initiating the ketogenic diet, it was effective (greater than a 50% reduction in seizure frequency) in 31.6% of patients. We did not find a link between rate of efficacy for the ketogenic diet and etiologies of epilepsy, nor did we find a link between the rate of efficacy for the ketogenic diet and cerebrospinal fluid pterins and biogenic amines concentrations. However, we found statistically significant differences for lysine and arginine values in the cerebrospinal fluid between ketogenic diet responders and nonresponders, but not for the other amino acids analyzed. Significance The values of some amino acids were significantly different in relationship with the ketogenic diet efficacy; however, the epilepsy etiology and the cerebrospinal fluid biogenic amine and pterin values were not.

Pharmacological chaperones are small compounds that correct the folding of mutant proteins, and represent a promising therapeutic strategy for misfolding diseases. We have performed a screening of 10,000 compounds searching for pharmacological chaperones of tyrosine hydroxylase (TH), the tetrahydrobiopterin (BH4)-dependent enzyme that catalyzes the rate-limiting step in the synthesis of catecholamines. A large number of compounds bound to human TH, isoform 1 (hTH1), but only twelve significantly protected wild-type (hTH1-wt) and mutant TH-R233H (hTH1-p.R202H), associated to the rare neurological disorder TH deficiency (THD), from time-dependent loss of activity. Three of them (named compounds 2, 4 and 5) were subjected to detailed characterization of their functional and molecular effects. Whereas compounds 2 and 4 had a characteristic pharmacological chaperone (stabilizing) effect, compound 5 protected the activity in a higher extent than expected from the low conformational stabilization exerted on hTH1. Compounds 4 and 5 were weak competitive inhibitors with respect to the cofactor BH4 and, as seen by electron paramagnetic resonance, they induced small changes to the first coordination sphere of the catalytic iron. Molecular docking also indicated active-site location with coordination to the iron through a pyrimidine nitrogen atom. Interestingly, compound 5 increased TH activity in cells transiently transfected with either hTH1-wt or the THD associated mutants p.L205P, p.R202H and p.Q381K without affecting the steady-state TH protein levels. This work revealed different mechanisms for the action of pharmacological chaperones and identifies a subtype of compounds that preserve TH activity by weak binding to the catalytic iron. This article is part of a Special Issue entitled: Cofactor-dependent proteins: Evolution, chemical diversity and bio-applications.

We aimed to study the cerebrospinal fluid (CSF) selenium (Se) status in pediatric patients with neurologic disorders and to assess the relationship between CSF Se concentrations, proteins, glutathione peroxidase (GPx) activity, and patient clinical data. We analyzed CSF Se by inductively coupled plasma-mass spectrometry (ICP-MS) in 212 patients with several neurologic conditions. Student's t -test was applied to compare CSF Se values from patients with those of controls. Single and multiple correlation studies were applied to assess the association between the different variables. Nineteen patients presented with abnormal CSF Se concentrations when compared with our reference values established for the different groups of age (group 1: 1–30 days; 1.8–4.7 µg/L; group 2: 1–36 months; 0.68–3.0 µg/L; group 3: 4–18 years; 0.73–2.13 µg/L) associated with different clinical conditions. Ten had decreased CSF Se levels and nine had increased levels. A positive correlation between CSF Se and GPx activity ( r = 0.586; p r = 0.387; p r = 0.898; p

Cerebral folate deficiency is defined as any neurological condition associated with low cerebrospinal fluid folate concentrations. It is becoming increasingly associated with several neurological diseases, either genetic or environmental. Treatment of cerebral folate deficiency by folate supplementation is generally effective, improving the neurological outcome of some patients. However, to treat cerebral folate deficiency, the proper choice of one of the available folate forms is essential. The distinct brain folate metabolism features compared with peripheral folate metabolic pathways strongly suggest the investigation of different folate forms, such as the biologically active folinic acid and 5-methyltetrahydrofolate, since they are efficiently transported to the brain. Regarding the oral doses of the different folate forms, despite the fact that there are some recommendations, there is no general consensus. Further investigation and designing clinical trials are advisable to elucidate these aspects.

Bachmann-Gagescu, Ruxandra/0000-0002-3571-5271; O'Roak, Brian/0000-0002-4141-0095; Isabella, Christine/0000-0003-0786-7240; Blue, Elizabeth/0000-0002-0633-0305; , Beyhan/0000-0002-9620-5021 WOS: 000358443800002 PubMed: 26092869 Background Joubert syndrome (JS) is a recessive neurodevelopmental disorder characterised by hypotonia, ataxia, cognitive impairment, abnormal eye movements, respiratory control disturbances and a distinctive mid-hindbrain malformation. JS demonstrates substantial phenotypic variability and genetic heterogeneity. This study provides a comprehensive view of the current genetic basis, phenotypic range and gene-phenotype associations in JS. Methods We sequenced 27 JS-associated genes in 440 affected individuals (375 families) from a cohort of 532 individuals (440 families) with JS, using molecular inversion probe-based targeted capture and next-generation sequencing. Variant pathogenicity was defined using the Combined Annotation Dependent Depletion algorithm with an optimised score cut-off. Results We identified presumed causal variants in 62% of pedigrees, including the first B9D2 mutations associated with JS. 253 different mutations in 23 genes highlight the extreme genetic heterogeneity of JS. Phenotypic analysis revealed that only 34% of individuals have a 'pure JS' phenotype. Retinal disease is present in 30% of individuals, renal disease in 25%, coloboma in 17%, polydactyly in 15%, liver fibrosis in 14% and encephalocele in 8%. Loss of CEP290 function is associated with retinal dystrophy, while loss of TMEM67 function is associated with liver fibrosis and coloboma, but we observe no clear-cut distinction between JS subtypes. Conclusions This work illustrates how combining advanced sequencing techniques with phenotypic data addresses extreme genetic heterogeneity to provide diagnostic and carrier testing, guide medical monitoring for progressive complications, facilitate interpretation of genome-wide sequencing results in individuals with a variety of phenotypes and enable gene-specific treatments in the future. Swiss NSFSwiss National Science Foundation (SNSF) [PZ00P3_142404/1]; National Institutes of HealthUnited States Department of Health & Human ServicesNational Institutes of Health (NIH) - USA [K23NS45832, K24HD046712, R01NS064077]; March of Dimes Basil O'Connor Starter Scholar Research AwardMarch of Dimes; Arc of Washington Trust Fund; University of Washington Intellectual and Developmental Disabilities Research Center Genetics Core (National Institutes of Health)United States Department of Health & Human ServicesNational Institutes of Health (NIH) - USA [U54HD083091]; National Human Genome Research InstituteUnited States Department of Health & Human ServicesNational Institutes of Health (NIH) - USANIH National Human Genome Research Institute (NHGRI); National Heart, Lung and Blood InstituteUnited States Department of Health & Human ServicesNational Institutes of Health (NIH) - USANIH National Heart Lung & Blood Institute (NHLBI) [1U54HG006493] RB-G was supported by a Swiss NSF grant Ambizione-SCORE PZ00P3_142404/1. The following authors received support from the National Institutes of Health: M.A.P. K23NS45832, I.A.G. K24HD046712, D.D R01NS064077. D.D. also received funding from a March of Dimes Basil O'Connor Starter Scholar Research Award, The Arc of Washington Trust Fund, and private donations from families of children with Joubert syndrome. The work was also supported by the University of Washington Intellectual and Developmental Disabilities Research Center Genetics Core (National Institutes of Health U54HD083091). Sequencing was provided by the University of Washington Center for Mendelian Genomics (UW CMG) and was funded by the National Human Genome Research Institute and the National Heart, Lung and Blood Institute grant 1U54HG006493 to Drs Debbie Nickerson, JS and Michael Bamshad.

Standardization of culture methods for human pluripotent stem cell (PSC) neural differentiation can greatly contribute to the development of novel clinical advancements through the comprehension of neurodevelopmental diseases. Here, we report an approach that reproduces neural commitment from human induced pluripotent stem cells using dual-SMAD inhibition under defined conditions in a vitronectin-based monolayer system. By employing this method it was possible to obtain neurons derived from both control and Rett syndrome patients' pluripotent cells. During differentiation mutated cells displayed alterations in the number of neuronal projections, and production of Tuj1 and MAP2-positive neurons. Although investigation of a broader number of patients would be required, these observations are in accordance with previous studies showing impaired differentiation of these cells. Consequently, our experimental methodology was proved useful not only for the generation of neural cells, but also made possible to compare neural differentiation behavior of different cell lines under defined culture conditions. This study thus expects to contribute with an optimized approach to study the neural commitment of human PSCs, and to produce patient-specific neural cells that can be used to gain a better understanding of disease mechanisms.

Pyridoxal phosphate (PLP) is the active form of vitamin B6 and a cofactor in many enzyme reactions including neurotransmitter metabolism. PLP metabolism disturbances may mostly lead to refractory seizures. In this report, we review the main pathophysiological factors related with PLP deficiency and our experience in PLP treatment in pediatric patients with low-normal cerebrospinal fluid PLP values who presented epilepsy. Only one case had a definite diagnosis (Phelan-McDermid syndrome). The results of extensive metabolic workups and targeted genetic studies were normal for all patients. In 5 cases, the response to PLP supplementation (10-30mg/kg/d) was initially positive. PLP adverse reactions were noticed in 4 patients and PLP was discontinued; however, one of the most noticeable symptoms was an asymptomatic increase in liver enzymes. These negative results with PLP supplementation are worth reporting, to improve the information we use to treat our patients.

Mitochondrial diseases exhibit significant clinical and genetic heterogeneity. Mitochondria are highly dynamic organelles that are the major contributor of adenosine triphosphate, through oxidative phosphorylation. These disorders may be developed at any age, with isolated or multiple system involvement, and in any pattern of inheritance. Defects in the mitochondrial respiratory chain impair energy production and almost invariably involve skeletal muscle and peripheral nerves, causing exercise intolerance, cramps, recurrent myoglobinuria, or fixed weakness, which often affects extraocular muscles and results in droopy eyelids (ptosis), progressive external ophthalmoplegia, peripheral ataxia, and peripheral polyneuropathy. This review describes the main neuromuscular symptomatology through different syndromes reported in the literature and from our experience. We want to highlight the importance of searching for the "clue clinical signs" associated with inheritance pattern as key elements to guide the complex diagnosis process and genetic studies in mitochondrial diseases.

Melatonin is synthesized from serotonin and it is excreted as sulphatoxymelatonin in urine. We aim to evaluate urinary sulphatoxymelatonin as a biomarker of brain serotonin status in a cohort of patients with mutations in genes related to serotonin biosynthesis. We analized urinary sulphatoxymelatonin from 65 healthy subjects and from 28 patients with genetic defects. A total of 18 patients were studied: 14 with autosomal dominant and recessive guanosine triphosphate cyclohydrolase-I deficiency; 3 with sepiapterin reductase deficiency; and 1 with aromatic L-amino acid decarboxylase deficiency. Further 11 patients were studied after receiving serotoninergic treatment (serotonin precursors, monoamine oxidase inhibitors, selective serotonin re-uptake inhibitors): 5 with aromatic L-amino acid decarboxylase deficiency; 1 with sepiapterin reductase deficiency; 3 with dihydropteridine reductase deficiency; and 2 with 6-pyruvoyltetrahydropterin synthase deficiency. Among the patients without therapy, 6 presented low urinary sulphatoxymelatonin values, while most of the patients with guanosine triphosphate cyclohydrolase-I deficiency showed normal values. 5 of 11 patients under treatment presented low urine sulphatoxymelatonin values. Thus, decreased excretion of sulphatoxymelatonin is frequently observed in cases with severe genetic disorders affecting serotonin biosynthesis. In conclusion, sulphatoxymelatonin can be a good biomarker to estimate serotonin status in the brain, especially for treatment monitoring purposes.

Inactivating mutations in the BCKDK gene, which codes for the kinase responsible for the negative regulation of the branched-chain α-keto acid dehydrogenase complex (BCKD), have recently been associated with a form of autism in three families. In this work, two novel exonic BCKDK mutations, c.520C>G/p.R174G and c.1166T>C/p.L389P, were identified at the homozygous state in two unrelated children with persistently reduced body fluid levels of branched-chain amino acids (BCAAs), developmental delay, microcephaly, and neurobehavioral abnormalities. Functional analysis of the mutations confirmed the missense character of the c.1166T>C change and showed a splicing defect r.[520c>g;521_543del]/p.R174Gfs1*, for c.520C>G due to the presence of a new donor splice site. Mutation p.L389P showed total loss of kinase activity. Moreover, patient-derived fibroblasts showed undetectable (p.R174Gfs1*) or barely detectable (p.L389P) levels of BCKDK protein and its phosphorylated substrate (phospho-E1α), resulting in increased BCKD activity and the very rapid BCAA catabolism manifested by the patients' clinical phenotype. Based on these results, a protein-rich diet plus oral BCAA supplementation was implemented in the patient homozygous for p.R174Gfs1*. This treatment normalized plasma BCAA levels and improved growth, developmental and behavioral variables. Our results demonstrate that BCKDK mutations can result in neurobehavioral deficits in humans and support the rationale for dietary intervention.

The rapid analysis of genomic data is providing effective mutational confirmation in patients with clinical and biochemical hallmarks of a specific disease. This is the case for nonketotic hyperglycinemia (NKH), a Mendelian disorder causing seizures in neonates and early-infants, primarily due to mutations in the GLDC gene. However, understanding the impact of missense variants identified in this gene is a major challenge for the application of genomics into clinical practice. Herein, a comprehensive functional and structural analysis of 19 GLDC missense variants identified in a cohort of 26 NKH patients was performed. Mutant cDNA constructs were expressed in COS7 cells followed by enzymatic assays and Western blot analysis of the GCS P-protein to assess the residual activity and mutant protein stability. Structural analysis, based on molecular modeling of the 3D structure of GCS P-protein, was also performed. We identify hypomorphic variants that produce attenuated phenotypes with improved prognosis of the disease. Structural analysis allows us to interpret the effects of mutations on protein stability and catalytic activity, providing molecular evidence for clinical outcome and disease severity. Moreover, we identify an important number of mutants whose loss-of-functionality is associated with instability and, thus, are potential targets for rescue using folding therapeutic approaches.

Mitochondrial diseases (MD) are a group of genetic and acquired disorders which present significant diagnostic challenges. Here we report the disease characteristics of a large cohort of pediatric MD patients (n = 95) with a definitive genetic diagnosis, giving special emphasis on clinical muscle involvement, biochemical and histopathological features. Of the whole cohort, 51 patients harbored mutations in nuclear DNA (nDNA) genes and 44 patients had mutations in mitochondrial DNA (mtDNA) genes. The nDNA patients were more likely to have a reduction in muscle fiber succinate dehydrogenase (SDH) stains and in SDH-positive blood vessels, while a higher frequency of mtDNA patients had ragged red (RRF) and blue fibers. The presence of positive histopathological features was associated with ophthalmoplegia, myopathic facies, weakness and exercise intolerance. In 17 patients younger than two years of age, RRF and blue fibers were observed only in one case, six cases presented cytochrome c oxidase (COX) reduction/COX-fibers, SDH reduction was observed in five and all except one presented SDH-positive blood vessels. In conclusion, muscle involvement was a frequent finding in our series of MD patients, especially in those harboring mutations in mtDNA genes.

Warburg Micro syndrome and Martsolf syndrome (MS) are heterogeneous autosomal-recessive developmental disorders characterized by brain, eye, and endocrine abnormalities. Causative biallelic germline mutations have been identified in RAB3GAP1, RAB3GAP2, or RAB18, each of which encode proteins involved in membrane trafficking. This report provides an up to date overview of all known disease variants identified in 29 previously published families and 52 new families. One-hundred and forty-four Micro and nine Martsolf families were investigated, identifying mutations in RAB3GAP1 in 41% of cases, mutations in RAB3GAP2 in 7% of cases, and mutations in RAB18 in 5% of cases. These are listed in Leiden Open source Variation Databases, which was created by us for all three genes. Genotype-phenotype correlations for these genes have now established that the clinical phenotypes in Micro syndrome and MS represent a phenotypic continuum related to the nature and severity of the mutations present in the disease genes, with more deleterious mutations causing Micro syndrome and milder mutations causing MS. RAB18 has not yet been linked to the RAB3 pathways, but mutations in all three genes cause an indistinguishable phenotype, making it likely that there is some overlap. There is considerable genetic heterogeneity for these disorders and further gene identification will help delineate these pathways.

Background N -Methyl-D-aspartate receptors (NMDARs) play pivotal roles in synaptic development, plasticity, neural survival, and cognition. Despite recent reports describing the genetic association between de novo mutations of NMDAR subunits and severe psychiatric diseases, little is known about their pathogenic mechanisms and potential therapeutic interventions. Here we report a case study of a 4-year-old Rett-like patient with severe encephalopathy carrying a missense de novo mutation in GRIN2B (p.P553T) coding for the GluN2B subunit of NMDAR. Methods We generated a dynamic molecular model of mutant GluN2B-containing NMDARs. We expressed the mutation in cell lines and primary cultures, and we evaluated the putative morphological, electrophysiological, and synaptic plasticity alterations. Finally, we evaluated D-serine administration as a therapeutic strategy and translated it to the clinical practice. Results Structural molecular modeling predicted a reduced pore size of mutant NMDARs. Electrophysiological recordings confirmed this prediction and also showed gating alterations, a reduced glutamate affinity associated with a strong decrease of NMDA-evoked currents. Moreover, GluN2B(P553T)-expressing neurons showed decreased spine density, concomitant with reduced NMDA-evoked currents and impaired NMDAR-dependent insertion of GluA1 at stimulated synapses. Notably, the naturally occurring coagonist D-serine was able to attenuate hypofunction of GluN2B(p.P553T)-containing NMDARs. Hence, D-serine dietary supplementation was initiated. Importantly, the patient has shown remarkable motor, cognitive, and communication improvements after 17 months of D-serine dietary supplementation. Conclusions Our data suggest that hypofunctional NMDARs containing GluN2B(p.P553T) can contribute to Rett-like encephalopathy and that their potentiation by D-serine treatment may underlie the associated clinical improvement.

Brain serotonin deficiency is a heterogeneous condition whose etiology remains unknown in the majority of cases. Strong evidence supports a major role for brain serotonin deficiency in common conditions such as depression and other psychiatric and cognitive disorders, which are probably due to interactions between genetic and environmental factors. Mendelian monogenic conditions leading to brain serotonin deficiency have also been identified, but they are rare. These diseases are associated with defects in other neurotransmitters (primarily dopamine), and it is difficult to link serotonin deficiency with specific neurological syndromes. Secondary serotonin deficiency is also common. In adults, when serotonin deficiency is thought to contribute to neurological symptoms such as sleep disturbance and alterations in behavior, treatment with serotonin precursors may be useful.

This review deals with (1) hereditary diseases in the metabolism of γ-aminobutyric acid (GABA) and of a glycine receptor and (2) some inborn errors of monoamine metabolism. Disorders of the metabolism of glycine are treated in Chap. 21. A putative deficiency of glutamic-acid decarboxylase is a rare cause of early or late infantile pyridoxine-responsive convulsions. Two other defects of GABA catabolism are: the very rare, severe, and untreatable GABA transaminase deficiency and the much more frequent succinic semialdehyde dehydrogenase (SSADH) deficiency which, to some extent, responds to GABA transaminase inhibition. Hyperekplexia is a dominantly inherited defect of the α1 subunit of the glycine receptor; it is a cause of excessive startle responses treatable with clonazepam.

CoQ deficiency study group: et al., We evaluated the coenzyme Q₁₀ (CoQ) levels in patients who were diagnosed with mitochondrial oxidative phosphorylation (OXPHOS) and non-OXPHOS disorders (n = 72). Data from the 72 cases in this study revealed that 44.4% of patients showed low CoQ concentrations in either their skeletal muscle or skin fibroblasts. Our findings suggest that secondary CoQ deficiency is a common finding in OXPHOS and non-OXPHOS disorders. We hypothesize that cases of CoQ deficiency associated with OXPHOS defects could be an adaptive mechanism to maintain a balanced OXPHOS, although the mechanisms explaining these deficiencies and the pathophysiological role of secondary CoQ deficiency deserves further investigation., This work was supported by grants from the Instituto de Salud Carlos III (FIS: PI12/01683, PI14/00005, PI14/00028 and PI14/01962), the Explora Ciencia Program (SAF2013-50139-EXP), the Departamento de Ciencia, Tecnología, from Universidad del Gobierno de Aragón (Grupos Consolidados B33), the Fondo Europeo de Desarrollo Regional (FEDER Funding Program) from the European Union. The CIBERER is an initiative of the ISCIII. UCLH/UCL received a proportion of funding from the Department of Health sNIHR Biomedical Research Centers funding scheme.