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Neuromuscular disorders (NMD) with neonatal or perinatal onset are usually severe. The establishment of a definite diagnosis relies on the combination of clinical examination, enzymatic tests, muscle morphology analyses, and genetic investigations, and is essential to provide a vital prognosis, propose adequate genetic counseling, consider treatment options, and include the patients into clinical trials for innovative therapies. However, the recent and rapid advancements of panel, exome, and genome sequencing questions the utility of invasive muscle biopsies and the contribution of histological and ultrastructural studies of muscle sections to the diagnosis process. Here, we explored the relevance of muscle biopsies collected at the Institute of Myology in Paris over a period of more than 50 years (1970-2021) in light of the evolution of Sanger and next-generation sequencing (NGS) technologies. Altogether, 82% of the biopsies showed typical structural myofiber anomalies highly suggestive of specific NMD classes (congenital myopathies, metabolic myopathies, lower motor neuron (LMN) and neuromuscular junction (NMJ) disorders, muscular dystrophies, inflammatory myopathies), while the remaining 18% showed no or only non-specific histological abnormalities. The diagnosis success rate differed among the NMD classes and changed over time following the identification of major disease genes like SMN1 or DMD , shifting the focus to direct gene sequencing and reducing the necessity of muscle biopsies. Ultrastructural investigations were of particular importance for the diagnosis of congenital myopathies and less relevant for the other NMD categories. Typical myofiber lesions found in congenital myopathies as intranuclear rods in ACTA1-related nemaline myopathy are barely discernible under the light microscope and solely detectable by electron microscopy (EM). This shows that the higher resolution of EM is not only a feature complementing light microscopy, but also a powerful diagnostic method. From our experience, morphological muscle biopsy examinations were frequently accurate and either pointed to a group of myopathies or to single genes. In conclusion, this retrospective study describes a unique collection of neonatal muscle biopsies and illustrates that the thorough analysis of muscle sections was of major diagnostic relevance in the past and still plays an important role nowadays - either by directing purposeful gene sequencing or by complementing clinical findings and biochemical analysis methods. [ABSTRACT FROM AUTHOR]

Heterozygous pathogenic variants in GATAD2B gene have been related to the GATAD2B-associated neurodevelopmental disorders (GAND) characterized by neurodevelopmental delay with predominant language impairment, infantile hypotonia, macrocephaly, ophthalmological abnormalities, and dysmorphic facial features with nonspecific findings on brain magnetic resonance imaging (MRI). Occasionally, affected individuals exhibit drug responsive epilepsy, psychiatric disorders, and other extra-neurological comorbidities. We report a patient carrying a de novo heterozygous missense variant in GATAD2B gene. She presents a developmental and epileptic encephalopathy (DEE) with drug-resistant atypical absences. An extensive review of the literature did not show any similar phenotype. Our report broadens the electroclinical spectrum related to GATAD2B pathogenic variants and supports the inclusion of this monogenic etiology among the genetic causes of epilepsy with drug-resistant atypical absences, a group with few known genetic etiologies. PLAIN LANGUAGE SUMMARY: We describe a patient with drug-resistant atypical absences caused by a pathogenic variant in the GATAD2B gene. Mutations in the GATAD2B gene should be considered among the rare monogenic causes of atypical absences., (© 2025 The Author(s). Epilepsia Open published by Wiley Periodicals LLC on behalf of International League Against Epilepsy.)

Focal cortical dysplasia, hemimegalencephaly and cortical tubers are paediatric epileptogenic malformations of cortical development (MCDs) frequently pharmacoresistant and mostly treated surgically by the resection of epileptic cortex. Availability of cortical resection samples has allowed significant mechanistic discoveries directly from human material. Causal brain somatic or germline mutations in the AKT/PI3K/DEPDC5/MTOR genes have been identified. GABAA-mediated paradoxical depolarization, related to altered chloride (Cl-) homeostasis, has been shown to participate to ictogenesis in human paediatric MCDs. However, the link between genomic alterations and neuronal hyperexcitability is unclear. Here, we studied the post-translational interactions between the mTOR pathway and the regulation of cation-chloride cotransporters (CCCs), KCC2 and NKCC1, that are largely responsible for controlling intracellular Cl- and, ultimately, GABAergic transmission. For this study, 35 children (25 MTORopathies and 10 pseudo-controls, diagnosed by histology plus genetic profiling) were operated for drug-resistant epilepsy. Postoperative cortical tissues were recorded on a multi-electrode array to map epileptic activities. CCC expression level and phosphorylation status of the WNK1/SPAK-OSR1 pathway was measured during basal conditions and after pharmacological modulation. Direct interactions between mTOR and WNK1 pathway components were investigated by immunoprecipitation. Membranous incorporation of MCD samples in Xenopus laevis oocytes enabled measurement of the Cl- conductance and equilibrium potential for GABA. Of the 25 clinical cases, half harboured a somatic mutation in the mTOR pathway, and pS6 expression was increased in all MCD samples. Spontaneous interictal discharges were recorded in 65% of the slices. CCC expression was altered in MCDs, with a reduced KCC2/NKCC1 ratio and decreased KCC2 membranous expression. CCC expression was regulated by the WNK1/SPAK-OSR1 kinases through direct phosphorylation of Thr906 on KCC2, which was reversed by WNK1 and SPAK antagonists (N-ethylmaleimide and staurosporine). The mSIN1 subunit of MTORC2 was found to interact with SPAK-OSR1 and WNK1. Interactions between these key epileptogenic pathways could be reversed by the mTOR-specific antagonist rapamycin, leading to a dephosphorylation of CCCs and recovery of the KCC2/NKCC1 ratio. The functional effect of such recovery was validated by the restoration of the depolarizing shift in the equilibrium potential for GABA by rapamycin, measured after incorporation of MCD membranes into X. laevis oocytes, in line with a re-establishment of normal Cl- reversal potential. Our study deciphers a protein interaction network through a phosphorylation cascade between MTOR and WNK1/SPAK-OSR1 leading to deregulation of chloride cotransporters, increased neuronal Cl- levels and GABAA dysfunction in malformations of cortical development, linking genomic defects and functional effects and paving the way to target epilepsy therapy., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Guarantors of Brain.)

Objective: Complex epilepsies such as epileptic and developmental encephalopathies require multidisciplinary care throughout life. A coordinated transition program is therefore essential to provide optimal support for patients leaving pediatric for adult care. The aim of this study is to describe and evaluate our transition program for complex epilepsies, focusing on the last step in this program, that is, the multidisciplinary transition day hospital (MTDH)., Methods: We performed a retrospective observational study including patients with complex epilepsies who underwent the full steps of the transition program at Necker-Enfants Malades Hospital between May 2021 and June 2023, with a follow-up until February 2024. We described the cohort and detailed the interventions performed during the MTDH including medical, medicosocial, educational, daily life abilities, and laboratory and imaging assessments with the participation of one member of the adult team. We evaluated two indicators of our program: (1) the "adult first clinic attendance rate," defined by the percentage of patients attending their first adult clinic; and (2) the "return rate," defined by the percentage of patients who requested a pediatric encounter after their transfer., Results: Our cohort included 70 patients with a mean age of 19.1 years (interquartile range = 16.3-19.5). Eighty percent had an epilepsy syndrome diagnosis; 72.8% were treated with three or more antiseizure medications. All patients had their appointment at the adult clinic within 6 months of the day hospital, and only two families requested a pediatric encounter after the transfer., Significance: The transition program is key for an optimal transfer of patients with complex epilepsies to adult care. It requires a comprehensive multidisciplinary approach and provides a complete summary of the medical record. Our program secures a smooth landing in adult care and is a promising model to better manage the challenging transition process, especially in patients with complex epilepsy., (© 2024 The Author(s). Epilepsia published by Wiley Periodicals LLC on behalf of International League Against Epilepsy.)

Friedreich's Ataxia (FRDA) is the most common hereditary ataxia and is mainly caused by biallelic GAA repeat expansion in the FXN gene. Rare patients carrying FXN point mutations or intragenic deletions are reported. We describe the first FRDA patient with a chromosome 9 segmental Uniparental isoDisomy (UPiD) unmasking a homozygous FXN expansion initially undetected by TP-PCR. The child presented with a progressive proprioceptive ataxia associated with peripheral sensory neuronopathy and severe scoliosis. Whole genome sequencing (WGS) identified a maternal segmental Uniparental Isodisomy (UPiD) encompassing FXN. Short tandem repeats analysis on WGS showed a biallelic FXN expansion. The identification of a deletion in the primer-annealing region of the TP-PCR explained the initial TP-PCR failure. This is the first documented case of FRDA caused by segmental UPiD. This case highlights the complexity of the molecular diagnosis of FRDA, and emphasises the importance of integrating results from various technical diagnostic approaches., Competing Interests: Competing interests: The authors declare no competing interests. Ethics approval: We confirm that we have read the Journal’s position on issues involved in ethical publication and affirm that this report is consistent with those guidelines., (© 2024. The Author(s), under exclusive licence to European Society of Human Genetics.)

Neuromuscular disorders (NMD) with neonatal or early infantile onset are usually severe and differ in symptoms, complications, and treatment options. The establishment of a diagnosis relies on the combination of clinical examination, morphological analyses of muscle biopsies, and genetic investigations. Here, we re-evaluated and classified a unique collection of 535 muscle biopsies from NMD infants aged 0-6 months examined over a period of 52 years. We aimed to assess the importance and contribution of morphological muscle biopsy analyses for the establishment of a precise and accurate molecular diagnosis. Altogether, 82% of the biopsies showed typical structural myofiber anomalies highly suggestive of specific NMD classes (congenital myopathies, metabolic myopathies, lower motor neuron (LMN) and neuromuscular junction (NMJ) disorders, muscular dystrophies, inflammatory myopathies), while the remaining 18% showed no or only non-specific histological abnormalities. The diagnostic success rate differed among the NMD classes and was particularly high for congenital myopathies as illustrated by the identification of causative genes in 61% of cases. This is essentially due to the presence of characteristic histopathological hallmarks on biopsies visible by light or electron microscopy often pointing to specific genes. In contrast, metabolic myopathies commonly displayed non-specific features on muscle sections, led to the identification of causative genes in only 19% of the patients, and typically required additional enzymatic tests to establish a more precise diagnosis. The evolution of sequencing technologies fundamentally improved molecular diagnosis and also shifted the relevance of muscle biopsies within the diagnostic process. Depending on the clinical presentation of the patients, direct gene or panel sequencing may be the preferred method nowadays. However, histological and ultrastructural examinations of muscle sections are still frequently useful and can constitute an elemental step in the diagnostic process-either by directing purposeful gene sequencing or pointing to genes and pathogenic variants identified by next-generation sequencing (NGS), or by complementing clinical findings and biochemical analysis methods., Competing Interests: Declarations. Ethics approval and consent to participate: All patients and legal guardians consented to the publication of the clinical, histological, and genetic data. Molecular diagnosis was carried out with written informed consent from the patients or legal guardians. Muscle biopsy storage and usage were IRB-approved. Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

Purpose: RORA encodes the RAR-related orphan receptor-α (RORα), playing a pivotal role in cerebellar maturation and function. Here, we report the largest series of individuals with RORA-related-neurodevelopmental disorder (RORA-NDD)., Methods: Forty individuals (30 unrelated; 10 siblings from 4 families) carrying RORA pathogenic/likely pathogenic variants were collected through an international collaboration., Results: The 33 variants (29 de novo, 4 inherited, one shared), identified by genome/exome sequencing (n=21), chromosomal-microarray-analysis (n=7) or gene panels (n=4), included frameshift (n=18/33), missense (n=9/33) and stop-codon (n=6/33). Developmental disability (n=32/37), intellectual disability (n=22/32), and cerebellar signs (n=25/34) were the most striking clinical features. Cerebellar symptoms were divided into early-onset, late-onset and progressive subgroups. Cerebellar hypoplasia, atrophy, or both (n=16/25) were more frequent in individuals with missense variants in the DNA-binding-domain (DBD). Epilepsy (n=18/38), with prominent myoclonic seizure types (n=11/18), was classified in: i) genetic generalized epilepsy (n=10/18) with a syndromic diagnosis identifiable for six: epilepsy with eyelid myoclonia (n=5/6), epilepsy with myoclonic absence (n=1/6); ii) developmental and epileptic encephalopathy (n=5/18); and iii) unclassified (n=3/18). A participant with rapid deterioration of visual acuity and cone/rod dystrophy was reported., Conclusion: Missense variants in DBD correlate to a more severe cerebellar phenotype. The RORA-NDD triad comprises developmental disability, cerebellar features and a spectrum of myoclonic epilepsy., (Copyright © 2024. Published by Elsevier Inc.)

Biallelic pathogenic variants in CNTNAP2, a gene encoding the contactin-associated protein-like 2, have been reported in patients with various clinical presentations including intellectual disability (ID), autistic spectrum disorders (ASD), psychiatric disorders, and focal epilepsy rarely associated to focal cortical dysplasia. We report four children carrying novel biallelic CNTNAP2 pathogenic variants. They present global developmental delay, psychiatric disorders, and focal epilepsy. All patients displayed brain MRI abnormalities consistent with focal temporal dysplasia. One patient had a temporal resection before the availability of genetic testing. Focal cortical dysplasia represents a frequent finding related to focal refractory epilepsy in CNTNAP2 affected patients, and surgery seems to be ineffective in this setting. The genetic testing could therefore be impactful on treatment choices in refractory focal epilepsies., (Copyright © 2024 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

Epilepsy surgery may be a curative therapy for patients with drug-resistant epilepsies when focal lesions or foci are identified. Genetic testing is not yet routinely included in many presurgical evaluation programs although recent evidence support that finding a germline genetic mutation could help to better delineate the patient candidacy to surgery and provide valuable information on the expected surgery outcome. In this study, we report nine patients presenting drug-resistant focal epilepsy enrolled in presurgical evaluation. We show how the identification of genetic pathogenic variant in epilepsy known genes led to the interruption of the presurgical work-up and ruled out surgery in 7 of them. We observed that the co-existence of some recurrent clinical characteristics as early seizures' onset, frequent precipitating factors including fever, and developmental delay or intellectual disability may be useful markers for germline genetic pathogenic variants. In this group, genetic assessment should be mandatory during presurgical work up, mainly in patients with negative magnetic resonance imaging (MRI) or doubtful structural lesions. The integration of next generation targeted sequencing into the presurgical evaluation can improve the selection of candidates for resective surgery and fosters a personalized medicine approach with a better outcome. PLAINE LANGUAGE ABSTRACT: Genetic testing is not yet systematically included in the pre-surgical assessment of patients with drug-resistant focal epilepsies. In this study, through the description of nine patients, we underline how the integration of genomics into the presurgical work up can help in evaluating the patient candidacy to surgery and provide valuable information on expected surgery outcome., (© 2024 The Author(s). Epilepsia Open published by Wiley Periodicals LLC on behalf of International League Against Epilepsy.)

Background and Objectives: DNA polymerase subunit gamma (POLG) deficiency is likely the most frequent cause of nuclear-encoded mitochondrial disorders. POLG -related disorders reportedly constitute a spectrum of overlapping phenotypes from infancy to late adulthood. We retrospectively reviewed natural histories for 40 children carrying biallelic pathogenic POLG variants., Methods: The patients were identified by the French coordinating center for mitochondrial disorders (CARAMMEL), making this a large monocentric series on childhood-onset POLG deficiency., Results: Three patterns of clinical course and survival were observed, distinguished by main category of symptoms: neurologic, hepatic, and gastrointestinal. A total of 24 patients needed urgent neurointensive care for tonic-clonic seizures, myoclonic epilepsy, and status epilepticus, occasionally precipitated by valproate administration. Other neurologic symptoms included dystonia, cerebellar ataxia, and peripheral neuropathy. We report 6 POLG-deficient patients with polyradiculoneuropathy mimicking subacute Guillain-Barré syndrome and provide postgadolinium MRI evidence of diffuse cranial nerve root and cauda equina enhancement, suggesting these disorders have an inflammatory component. Children presenting with enteral nervous system involvement had vomiting, gastroparesis, and chronic intestinal pseudo-obstruction. They had later ages of onset and lived much longer. Primarily, hepatic presentations had the earliest onset and shortest survivals. Secondary hepatic failure was frequently precipitated by valproate administration given before diagnosis to patients with focal impaired awareness seizures or absence of seizures. These POLG deficiencies were often fatal, with age at death ranging from 3 months to 10 years, with a significant difference in survival between the 3 clinical forms; 6 of the 40 children did survive. No genotype-phenotype correlations were found for the 3 clinical course types., Discussion: The study demonstrates the prevalence of neurologic presentation and the extent of central, peripheral, and autonomous nervous system involvement in 60% of patients. Most of the patients with early onset and rapidly fatal hepatic failure did not live long enough to develop neurologic symptoms. The study revealed a new clinical form of POLG deficiency presenting with neurodigestive symptoms with longer lifespan. We also propose that POLG deficiency should be considered in children presenting with unexplained polyradiculoneuropathy, demyelinating neuropathy, and elevated CSF protein. Finally, valproate administration remains a notable cause of avoidable death in POLG-deficient patients., Competing Interests: The authors report no relevant disclosures. Go to Neurology.org/NG for full disclosures., (Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology.)

Objective: The objective of this study was to evaluate the implementation of NGS within the French mitochondrial network, MitoDiag, from targeted gene panels to whole exome sequencing (WES) or whole genome sequencing (WGS) focusing on mitochondrial nuclear-encoded genes., Methods: Over 2000 patients suspected of Primary Mitochondrial Diseases (PMD) were sequenced by either targeted gene panels, WES or WGS within MitoDiag. We described the clinical, biochemical, and molecular data of 397 genetically confirmed patients, comprising 294 children and 103 adults, carrying pathogenic or likely pathogenic variants in nuclear-encoded genes., Results: The cohort exhibited a large genetic heterogeneity, with the identification of 172 distinct genes and 253 novel variants. Among children, a notable prevalence of pathogenic variants in genes associated with oxidative phosphorylation (OXPHOS) functions and mitochondrial translation was observed. In adults, pathogenic variants were primarily identified in genes linked to mtDNA maintenance. Additionally, a substantial proportion of patients (54% (42/78) and 48% (13/27) in children and adults, respectively), undergoing WES or WGS testing displayed PMD mimics, representing pathologies that clinically resemble mitochondrial diseases., Interpretation: We reported the largest French cohort of patients suspected of PMD with pathogenic variants in nuclear genes. We have emphasized the clinical complexity of PMD and the challenges associated with recognizing and distinguishing them from other pathologies, particularly neuromuscular disorders. We confirmed that WES/WGS, instead of panel approach, was more valuable to identify the genetic basis in patients with "possible" PMD and we provided a genetic testing flowchart to guide physicians in their diagnostic strategy., (© 2024 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association.)

Introduction and Methods: We report two series of individuals with DDX3X variations, one (48 individuals) from physicians and one (44 individuals) from caregivers., Results: These two series include several symptoms in common, with fairly similar distribution, which suggests that caregivers' data are close to physicians' data. For example, both series identified early childhood symptoms that were not previously described: feeding difficulties, mean walking age, and age at first words., Discussion: Each of the two datasets provides complementary knowledge. We confirmed that symptoms are similar to those in the literature and provides more details on feeding difficulties. Caregivers considered that the symptom attention-deficit/hyperactivity disorder were most worrisome. Both series also reported sleep disturbance. Recently, anxiety has been reported in individuals with DDX3X variants. We strongly suggest that attention-deficit/hyperactivity disorder, anxiety, and sleep disorders need to be treated., (© 2024 The Authors. Molecular Genetics & Genomic Medicine published by Wiley Periodicals LLC.)

DExD/H-box RNA helicases (DDX/DHX) are encoded by a large paralogous gene family; in a subset of these human helicase genes, pathogenic variation causes neurodevelopmental disorder (NDD) traits and cancer. DHX9 encodes a BRCA1-interacting nuclear helicase regulating transcription, R-loops, and homologous recombination and exhibits the highest mutational constraint of all DDX/DHX paralogs but remains unassociated with disease traits in OMIM. Using exome sequencing and family-based rare-variant analyses, we identified 20 individuals with de novo, ultra-rare, heterozygous missense or loss-of-function (LoF) DHX9 variant alleles. Phenotypes ranged from NDDs to the distal symmetric polyneuropathy axonal Charcot-Marie-Tooth disease (CMT2). Quantitative Human Phenotype Ontology (HPO) analysis demonstrated genotype-phenotype correlations with LoF variants causing mild NDD phenotypes and nuclear localization signal (NLS) missense variants causing severe NDD. We investigated DHX9 variant-associated cellular phenotypes in human cell lines. Whereas wild-type DHX9 was restricted to the nucleus, NLS missense variants abnormally accumulated in the cytoplasm. Fibroblasts from an individual with an NLS variant also showed abnormal cytoplasmic DHX9 accumulation. CMT2-associated missense variants caused aberrant nucleolar DHX9 accumulation, a phenomenon previously associated with cellular stress. Two NDD-associated variants, p.Gly411Glu and p.Arg761Gln, altered DHX9 ATPase activity. The severe NDD-associated variant p.Arg141Gln did not affect DHX9 localization but instead increased R-loop levels and double-stranded DNA breaks. Dhx9 -/- mice exhibited hypoactivity in novel environments, tremor, and sensorineural hearing loss. All together, these results establish DHX9 as a critical regulator of mammalian neurodevelopment and neuronal homeostasis., Competing Interests: Declaration of interests J.R.L. has stock ownership in 23andMe, is a paid consultant for Genome International, and is a co-inventor on multiple US and European patents related to molecular diagnostics for inherited neuropathies, eye diseases, genomic disorders, and bacterial genomic fingerprinting. The Department of Molecular and Human Genetics at the Baylor College of Medicine receives revenue from clinical genetic testing conducted at Baylor Genetics (BG) Laboratories. F.M. and T.S.-S. are employees of GeneDx., (Copyright © 2023 American Society of Human Genetics. All rights reserved.)

Background and Purpose: Stroke-like episodes (SLEs) are defined as acute onset of neurological symptoms mimicking a stroke and radiological lesions non-congruent to vascular territory. We aimed to analyze the acute clinical and radiological features of SLEs to determine their pathophysiology., Methods: We performed a monocenter retrospective analysis of 120 SLEs in 60 children over a 20-year period. Inclusion criteria were compatible clinical symptoms and stroke-like lesions on brain magnetic resonance imaging (MRI; performed for all 120 events) with focal hyperintensity on diffusion-weighted imaging in a non-vascular territory., Results: Three groups were identified: children with mitochondrial diseases (n = 22) involving mitochondrial DNA mutations (55%) or nuclear DNA mutations (45%); those with other metabolic diseases or epilepsy disorders (n = 22); and those in whom no etiology was found despite extensive investigations (n = 16). Age at first SLE was younger in the group with metabolic or epilepsy disorders (18 months vs. 128 months; p < 0.0001) and an infectious trigger was more frequent (69% vs. 20%; p = 0.0001). Seizures occurred in 75% of episodes, revealing 50% episodes of SLEs and mainly leading to status epilepticus (90%). Of the 120 MRI scans confirming the diagnosis, 28 were performed within a short and strict 48-h period and were further analyzed to better understand the underlying mechanisms. The scans showed primary cortical hyperintensity (n = 28/28) with decreased apparent diffusion coefficient in 52% of cases. Systematic hyperperfusion was found on spin labeling sequences when available (n = 18/18)., Conclusion: Clinical and radiological results support the existence of a vicious circle based on two main mechanisms: energy deficit and neuronal hyperexcitability at the origin of SLE., (© 2023 The Authors. European Journal of Neurology published by John Wiley & Sons Ltd on behalf of European Academy of Neurology.)

A critical step in preserving protein homeostasis is the recognition, binding, unfolding, and translocation of protein substrates by six AAA-ATPase proteasome subunits (ATPase-associated with various cellular activities) termed PSMC1-6, which are required for degradation of proteins by 26 S proteasomes. Here, we identified 15 de novo missense variants in the PSMC3 gene encoding the AAA-ATPase proteasome subunit PSMC3/Rpt5 in 23 unrelated heterozygous patients with an autosomal dominant form of neurodevelopmental delay and intellectual disability. Expression of PSMC3 variants in mouse neuronal cultures led to altered dendrite development, and deletion of the PSMC3 fly ortholog Rpt5 impaired reversal learning capabilities in fruit flies. Structural modeling as well as proteomic and transcriptomic analyses of T cells derived from patients with PSMC3 variants implicated the PSMC3 variants in proteasome dysfunction through disruption of substrate translocation, induction of proteotoxic stress, and alterations in proteins controlling developmental and innate immune programs. The proteostatic perturbations in T cells from patients with PSMC3 variants correlated with a dysregulation in type I interferon (IFN) signaling in these T cells, which could be blocked by inhibition of the intracellular stress sensor protein kinase R (PKR). These results suggest that proteotoxic stress activated PKR in patient-derived T cells, resulting in a type I IFN response. The potential relationship among proteosome dysfunction, type I IFN production, and neurodevelopment suggests new directions in our understanding of pathogenesis in some neurodevelopmental disorders.

Transcription of mitochondrial DNA generates long polycistronic precursors whose nucleolytic cleavage yields the individual mtDNA-encoded transcripts. In most cases, this cleavage occurs at the 5'- and 3'-ends of tRNA sequences by the concerted action of RNAseP and RNaseZ/ELAC2 endonucleases, respectively. Variants in the ELAC2 gene have been predominantly linked to severe to mild cardiomyopathy that, in its milder forms, is accompanied by variably severe neurological presentations. Here, we report five patients from three unrelated families. Four of the patients presented mild to moderate cardiomyopathy and one died at 1 year of age, one patient had no evidence of cardiomyopathy. The patients had variable neurological presentations that included intellectual disability, ataxia, refractory epilepsy, neuropathy and deafness. All patients carried previously unreported missense and nonsense variants. Enzymatic analyses showed multiple OXPHOS deficiencies in biopsies from two patients, whereas immunoblot analyses revealed a decreased abundance of ELAC2 in fibroblasts from three patients. Northern blot analysis revealed an accumulation of unprocessed mt-tRNA Val -precursor consistent with the role of ELAC2 in transcript processing. Our study expands the genetic spectrum of ELAC2 -linked disease and suggests that cardiomyopathy is not an invariably present clinical hallmark of this pathology.

The transmembrane protein TMEM147 has a dual function: first at the nuclear envelope, where it anchors lamin B receptor (LBR) to the inner membrane, and second at the endoplasmic reticulum (ER), where it facilitates the translation of nascent polypeptides within the ribosome-bound TMCO1 translocon complex. Through international data sharing, we identified 23 individuals from 15 unrelated families with bi-allelic TMEM147 loss-of-function variants, including splice-site, nonsense, frameshift, and missense variants. These affected children displayed congruent clinical features including coarse facies, developmental delay, intellectual disability, and behavioral problems. In silico structural analyses predicted disruptive consequences of the identified amino acid substitutions on translocon complex assembly and/or function, and in vitro analyses documented accelerated protein degradation via the autophagy-lysosomal-mediated pathway. Furthermore, TMEM147-deficient cells showed CKAP4 (CLIMP-63) and RTN4 (NOGO) upregulation with a concomitant reorientation of the ER, which was also witnessed in primary fibroblast cell culture. LBR mislocalization and nuclear segmentation was observed in primary fibroblast cells. Abnormal nuclear segmentation and chromatin compaction were also observed in approximately 20% of neutrophils, indicating the presence of a pseudo-Pelger-Huët anomaly. Finally, co-expression analysis revealed significant correlation with neurodevelopmental genes in the brain, further supporting a role of TMEM147 in neurodevelopment. Our findings provide clinical, genetic, and functional evidence that bi-allelic loss-of-function variants in TMEM147 cause syndromic intellectual disability due to ER-translocon and nuclear organization dysfunction., Competing Interests: Declaration of interests S.A., I.K., J.P.B., and A.B.-A. are employees of Centogene GmbH., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Objective: γ-Aminobutyric acid (GABA) A -receptor subunit variants have recently been associated with neurodevelopmental disorders and/or epilepsy. The phenotype linked with each gene is becoming better known. Because of the common molecular structure and physiological role of these phenotypes, it seemed interesting to describe a putative phenotype associated with GABA A -receptor-related disorders as a whole and seek possible genotype-phenotype correlations., Methods: We collected clinical, electrophysiological, therapeutic, and molecular data from patients with GABA A -receptor subunit variants (GABRA1, GABRB2, GABRB3, and GABRG2) through a national French collaboration using the EPIGENE network and compared these data to the one already described in the literature., Results: We gathered the reported patients in three epileptic phenotypes: 15 patients with fever-related epilepsy (40%), 11 with early developmental epileptic encephalopathy (30%), 10 with generalized epilepsy spectrum (27%), and 1 patient without seizures (3%). We did not find a specific phenotype for any gene, but we showed that the location of variants on the transmembrane (TM) segment was associated with a more severe phenotype, irrespective of the GABA A -receptor subunit gene, whereas N-terminal variants seemed to be related to milder phenotypes., Significance: GABA A -receptor subunit variants are associated with highly variable phenotypes despite their molecular and physiological proximity. None of the genes described here was associated with a specific phenotype. On the other hand, it appears that the location of the variant on the protein may be a marker of severity. Variant location may have important weight in the development of targeted therapeutics., (© 2022 The Authors. Epilepsia published by Wiley Periodicals LLC on behalf of International League Against Epilepsy.)

Vacuolar-type H+-ATPase (V-ATPase) is a multimeric complex present in a variety of cellular membranes that acts as an ATP-dependent proton pump and plays a key role in pH homeostasis and intracellular signalling pathways. In humans, 22 autosomal genes encode for a redundant set of subunits allowing the composition of diverse V-ATPase complexes with specific properties and expression. Sixteen subunits have been linked to human disease. Here we describe 26 patients harbouring 20 distinct pathogenic de novo missense ATP6V1A variants, mainly clustering within the ATP synthase α/β family-nucleotide-binding domain. At a mean age of 7 years (extremes: 6 weeks, youngest deceased patient to 22 years, oldest patient) clinical pictures included early lethal encephalopathies with rapidly progressive massive brain atrophy, severe developmental epileptic encephalopathies and static intellectual disability with epilepsy. The first clinical manifestation was early hypotonia, in 70%; 81% developed epilepsy, manifested as developmental epileptic encephalopathies in 58% of the cohort and with infantile spasms in 62%; 63% of developmental epileptic encephalopathies failed to achieve any developmental, communicative or motor skills. Less severe outcomes were observed in 23% of patients who, at a mean age of 10 years and 6 months, exhibited moderate intellectual disability, with independent walking and variable epilepsy. None of the patients developed communicative language. Microcephaly (38%) and amelogenesis imperfecta/enamel dysplasia (42%) were additional clinical features. Brain MRI demonstrated hypomyelination and generalized atrophy in 68%. Atrophy was progressive in all eight individuals undergoing repeated MRIs. Fibroblasts of two patients with developmental epileptic encephalopathies showed decreased LAMP1 expression, Lysotracker staining and increased organelle pH, consistent with lysosomal impairment and loss of V-ATPase function. Fibroblasts of two patients with milder disease, exhibited a different phenotype with increased Lysotracker staining, decreased organelle pH and no significant modification in LAMP1 expression. Quantification of substrates for lysosomal enzymes in cellular extracts from four patients revealed discrete accumulation. Transmission electron microscopy of fibroblasts of four patients with variable severity and of induced pluripotent stem cell-derived neurons from two patients with developmental epileptic encephalopathies showed electron-dense inclusions, lipid droplets, osmiophilic material and lamellated membrane structures resembling phospholipids. Quantitative assessment in induced pluripotent stem cell-derived neurons identified significantly smaller lysosomes. ATP6V1A-related encephalopathy represents a new paradigm among lysosomal disorders. It results from a dysfunctional endo-lysosomal membrane protein causing altered pH homeostasis. Its pathophysiology implies intracellular accumulation of substrates whose composition remains unclear, and a combination of developmental brain abnormalities and neurodegenerative changes established during prenatal and early postanal development, whose severity is variably determined by specific pathogenic variants., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)