The phenotypic spectrum associated with pathogenic ARID1B variants is remarkably broad, ranging from classic Coffin-Siris syndrome to non-syndromic intellectual disability and autism spectrum disorders. While speech delay, motor impairments and learning difficulties are well documented, brain imaging investigations remain scarce in this population. We combined multimodal neuroimaging and neuropsychological assessments in 12 patients carrying pathogenic ARID1B variants (age = 13.8 ± 4.7 years) and 34 age-matched healthy controls. Whole-brain voxel-wise analyses included arterial spin labelling to measure cerebral blood flow (CBF) at rest and voxel-based morphometry to assess grey matter density. To investigate white matter abnormalities, we performed fixel-based analysis in a subgroup of 7 patients and 17 age-matched controls. While patients showed pronounced language, motor and social impairments, their memory performance ( + 5 SD) largely exceeded other cognitive and motor skills. Whole-brain voxel-wise analyses showed a significant bilateral increase of CBF at rest in several limbic structures, including hippocampi and visual areas. They also showed significant decrease in grey matter density and fibre density in the same limbic structures, language, motor and social circuits. This paradoxical coexistence of hyperperfusion and structural deficits within memory networks suggests functional resilience or compensatory mechanisms. These preserved visual and memory functions strongly contrasted with their impaired language, motor, and social abilities. Patients appeared to rely on visual cues and memory to compensate for deficits in verbal communication. These findings support the development of individualized and innovative interventions that build on preserved visual and memory abilities in children with pathogenic ARID1B variants.

Mitochondria have long been known to be involved in the regulation of innate immune response. We questioned whether cultured skin fibroblasts of patients suffering from mitochondrial diseases are valuable biological resources for the study of interferon signaling. Expression of interferon-stimulated genes was measured in control cells supplemented with interferon and in cultured fibroblasts of patients carrying pathogenic variants in mitochondrial disease-causing genes. Control fibroblasts showed a strong expression of interferon-stimulated genes in response to interferon, but only 43% of patients' fibroblasts displayed increased interferon stimulated genes scores. Cytosolic mitochondrial DNA and RNA were quantified by immunofluorescence and confocal microscopy. No correlation between elevated interferon response and cytosolic mitochondrial DNA or RNA release could be established. We found that cultured skin fibroblasts represent a valuable biological resource for the investigation of interferon signaling, but that abnormal interferon signaling is not always observed in patients with mitochondrial diseases. At variance to gene silencing in control fibroblasts, the lack of correlation between elevated interferon response and cytosolic mitochondrial DNA or RNA leakage in patients' fibroblasts questions the relevance of cellular models as illustrators of pathological situations in humans.

Background : Phelan–McDermid syndrome (PMS) is a neurodevelopmental disorder caused by pathogenic variants involving the SHANK3 gene, a key postsynaptic scaffolding protein regulating synaptic function. SHANK3 alterations range from sequence variants to large chromosomal deletions on chromosome 22q13. While SHANK3 haploinsufficiency alone produces core PMS features, larger deletions encompassing adjacent genes are associated with more severe motor, speech, and cognitive phenotypes, whereas smaller deletions may lead to distinct neurobehavioral profiles. Methods : We conducted a multimodal study integrating molecular genetics and neuropsychological assessment with structural MRI, voxel-based morphometry (VBM) and arterial spin labeling (ASL) perfusion imaging in 36 individuals with de novo SHANK3 variants, including 21 sequence variants and 15 deletions ranging from (68.64 kb to 8.7 Mb). Deletions were stratified into Class I (involving SHANK3 only or with ARSA , ACR , and/or RABL2B ) and Class II (all other deletions). Results : Class II deletions were strongly associated with cortico-subcortical atrophy (10/15 vs. 0/21; p = 0.00001) and corpus callosum abnormalities. The group with larger deletions (Class II) showed a distinctive anomaly of the forceps minor, characterized by marked enlargement and dysmorphism (8/8 vs 0 in other groups; p < 0.001) and severe nonverbal social communication deficits. This feature was absent in Class I deletions and sequence variants. A minimal 760 kb critical region, including CERK , TBC1D22A , CELSR1 , and GRAMD4 , was implicated in these anomalies. VBM analyses revealed widespread reductions in gray and white matter volumes in carriers of Class II deletions, predominantly in frontotemporal and parietal regions, whereas sequence variants showed no significant volume loss. ASL imaging demonstrated reduced cerebral blood flow in key regions of the social brain network, particularly within the bilateral superior temporal cortex. Limitations : Multimodal MRI without premedication remains challenging in children older than 5 years due to motion, particularly with longer acquisition times. Conclusions : The identification of a minimal overlapping deleted region encompassing multiple candidate genes supports the contribution of additional loci within 22q13 to disease expression. These findings refine genotype–phenotype correlations in PMS and provide evidence that the disorder associated with larger deletions may be regarded as a contiguous gene syndrome.

Small nuclear RNAs (snRNAs) are essential components of the spliceosome. De novo variants in snRNA genes RNU4-2 (ReNU syndrome), RNU5B-1 and RNU2-2 have been linked to dominant neurodevelopmental disorders (NDDs), revealing a large unexpected contribution of noncoding RNA genes to genetic diseases. Here, through international collaborations, we analyze systematically 200 potentially functional snRNA genes in a French cohort of 34,329 people with rare disorders. We report RNU2-2 variants in 141 individuals, including 35 with recurrent dominant pathogenic variants and 91 affected members from 73 families with biallelic variants. Recessive RNU2-2 NDD is at least twice as frequent as the dominant form and often involves a de novo variant in trans with an inherited allele, consistent with the high mutability of snRNA genes. Dominant and recessive RNU2-2 NDDs share overlapping clinical features, with frequent epilepsy. Blood transcriptomics and DNA methylation analyses revealed subtle, variant-specific effects on splicing and episignatures. Our results support a gradient-of-impact model bridging dominant and recessive inheritance, and establish RNU2-2 variants as a principal contributor to NDDs, nearly as prevalent as ReNU syndrome.

Variants in spliceosomal small nuclear RNA (snRNA) genes RNU4-2 (ReNU syndrome), RNU5B-1, and RNU2-2 have recently been linked to dominant neurodevelopmental disorders (NDDs), revealing a major, previously overlooked role for noncoding snRNAs in human disease. Here, we systematically analysed 200 potentially functional snRNA genes in a French cohort comprising 26,911 individuals with rare disorders and through international collaborations. We identify de novo and biallelic variants in RNU2-2 associated with both dominant and recessive NDDs in 126 individuals from 108 unrelated families. Recessive RNU2-2 NDD is at least twice as frequent as the dominant NDD caused by n.4G>A and n.35A>G, and often arises from a de novo variant in trans with an inherited allele, reflecting the high mutability of snRNA genes. Dominant and recessive RNU2-2-NDDs share overlapping clinical features with frequent epilepsy. Blood transcriptomics and DNA methylation analyses revealed subtle, variant-specific effects on splicing and episignatures. Our findings support a gradient-of-impact model and a continuum between dominant and recessive inheritance, establishing RNU2-2 variants as a frequent cause of NDDs, nearly as prevalent as ReNU syndrome.

Friedreich ataxia (FRDA) is the most common type of inherited ataxia. It is a neurodegenerative disorder characterized by progressive gait and limb ataxia, dysarthria, areflexia, and reduced proprioception and vibration sensation. Although a number of clinical trials have been conducted, there is currently no cure for this disease. In this article we review those clinical trials with a focus on the instruments used as endpoints to assess clinical progression, and discuss the potential benefits of integrating additional measures, including assessments from overlooked domains. We also review tools used to evaluate cognitive functions in individuals with FRDA, particularly those employing quantitative, objective, and time-based measures. We argue for the inclusion of cognitive and speech-related assessments in clinical trials, and examine the potential of developments in cognitive neuroscience and technology to address current measurement challenges and support more accurate and comprehensive evaluation of treatment effects. These innovations have the potential to complement existing approaches, enhance trial design, and advance clinical care.

BACKGROUND:The health of children exposed but uninfected by human immunodeficiency virus (HIV) requires long-term assessment, in particular in terms of neurological and cognitive development. Numerous confounding factors have hampered such assessment, and published data are contradictory. METHODS:Using data from the French National Health Data System from 2012 to 2022, we conducted a population-based matched cohort study on all live-born single children, including those born to mothers with HIV, all prenatally exposed to antiretrovirals (ARVs). The primary outcome was the diagnosis of neurodevelopmental disorders according to the International Classification of Diseases, 10th Revision. The recourse to specialized consultations likely to indirectly reflect neurodevelopmental symptoms was also evaluated. Incidence was assessed using the Cox survival model. RESULTS:Of 6 667 363 live-born singletons, 9035 were born to mothers with HIV, all exposed to ARVs during pregnancy. Children were followed for up to 11 years (average, 5.5 years). Overall, the incidence of neurodevelopmental disorders among exposed children was higher than in the general population, even after matching for 5 sociodemographic criteria and gestational age (hazard ratio, 1.24 [95% confidence interval, 1.04-1.47]). It was not possible to dissect the respective role of maternal infection from that of maternal treatment, as all children were coexposed to HIV and ARVs. However, among those exposed to tenofovir-emtricitabine, the ritonavir-boosted darunavir-based combination was significantly associated with a higher combined incidence of neurodevelopmental disorders and related specialized consultations than other protease inhibitors (log-rank P < .001). CONCLUSIONS:Children exposed to HIV and ARVs in utero have a higher risk of developing neurodevelopmental disorders of multifactorial origin.

STUDY QUESTION:Is preimplantation genetic testing for mitochondrial DNA (mtDNA) disorders (PGT-mt) feasible at early compaction and blastocyst stages? SUMMARY ANSWER:Pathogenic mtDNA variants segregate evenly among cell types and various lineages of a given embryo during preimplantation development, supporting the relevance of genetic analyses performed on Day 4 blastomere and on Day 5 or 6 trophectoderm (TE) samples. WHAT IS KNOWN ALREADY:PGT-mt is validated at cleavage stage (Day 3 of development). However, its feasibility at later stages is questionable, as little is known regarding the segregation of pathogenic mtDNA variants during preimplantation development. Since mtDNA replication is silenced until the blastocyst stage (Day 5 or 6), uneven mtDNA segregation between preimplantation embryo cellular lineages known as a 'bottleneck' effect, cannot be excluded, posing a challenge for PGT-mt. STUDY DESIGN, SIZE, DURATION:We analyzed 112 'mito' embryos carrying pathogenic mtDNA variants and 28 control embryos with mtDNA polymorphism. Heteroplasmy levels were assessed in single cells of the TE, in different parts of blastocysts (inner cell mass and TE), and at three time points of development, namely cleavage (Day 3), early compaction (Day 4), and blastocyst stages (Day 5 or 6). PARTICIPANTS/MATERIALS, SETTING, METHODS:As part of clinical PGT, a blastomere biopsy was performed at cleavage or early compaction stages (Day 3 or 4) on 112 'mito' and 21/28 control embryos. Further analysis was carried out at Day 5 or 6 on 51 embryos deemed unsuitable for uterine transfer and donated to research. Heteroplasmy levels were determined by semi-quantitative PCR amplification of (i) the mtDNA pathogenic variants with additional enzymatic digestion or (ii) the mtDNA polymorphic hypervariable region 2. MAIN RESULTS AND THE ROLE OF CHANCE:Here, we first show that mtDNA variants segregate evenly among blastomeres during early compaction (Day 4), supporting the feasibility of PGT-mt at this stage. We also found that mtDNA ratios remain stable between cleavage and blastocyst stages. Yet, the substantial variation of heteroplasmy levels occurring among single TE cells in 1/8 embryos suggests that PGT is only feasible when at least 5-10 cells are collected by standard TE biopsy. LIMITATIONS, REASONS FOR CAUTION:This study sheds light on mtDNA segregation in human preimplantation embryo development. Its limitation lies in the scarcity of the material and the small number of embryos carrying a specific pathogenic mtDNA variant. Furthermore, the study of single cells from TE was performed on control embryos only. WIDER IMPLICATIONS OF THE FINDINGS:By supporting the relevance of blastocyst biopsy in the context of PGT for pathogenic mtDNA variants, this study contributes to the general trend of postponing the biopsy to later stages of embryonic development. However, particular attention should be paid to the number of TE cells tested. Due to the potential variation of mutant load during in utero development, a control amniocentesis for evolutive pregnancies following the transfer of heteroplasmic embryos is still recommended. STUDY FUNDING/COMPETING INTEREST(S):This work was funded by 'Association Française contre les Myopathies/AFM Téléthon' (22112, 24317, 28525); and EUR G.E.N.E. (No. ANR-17-EURE-0013). The authors have no competing interests to declare. TRIAL REGISTRATION NUMBER:N/A.

Mitochondrial myopathies are progressive muscle disorders caused by impaired mitochondrial oxidative phosphorylation, leading to reduced adenosine triphosphate production. Skeletal muscles have a high energy demand and are often the first to be affected. In addition to muscular symptoms (muscle weakness, effort intolerance, fatigue), the disease can affect the central and peripheral nervous systems, as well as the heart, liver, kidneys and endocrine system (diabetes). Molecular genetic diagnostic is currently based on leukocyte DNA obtained from blood samples, considered less invasive than muscle biopsy. We report four patients from three families with mitochondrial myopathy associated with ptosis, sensorineural hearing loss, epilepsy, tubulointerstitial nephropathy and cardiomyopathy. Genetic studies identified MT-TF variants (m.586G > A, m.601G > A, m.616 T > C) with highly variable heteroplasmy levels in the same patient from one tissue to another (5 % to 70 % mutant load in circulating blood leukocytes and in muscle respectively). We emphasize the importance of performing mtDNA analysis on muscle DNA, even in patients with negative blood leukocytes mtDNA sequencing, if there is strong clinical suspicion of mitochondrial myopathy.

Pathogenic variants in POLG are involved in a large spectrum of neurological, gastrointestinal and liver impairments. Children affected with POLG-related disorders rarely exhibit peripheral neuropathy, the latter being most often described in adults as axonal polyneuropathy. Our aim was to focus on electrophysiological findings in young children affected with POLG-related disorder. We report herein 6 unrelated early-onset POLG patients presenting with an atypical and severe polyradiculoneuropathy mimicking Chronic Inflammatory Demyelinating Polyneuropathy (CIDP). All these patients also exhibited severe intestinal dysmotility and liver disease. Different compound heterozygous pathogenic variants in POLG were found and 4/6 patients shared the same heterozygous R232H variation. POLG-related disorders should therefore be considered in the setting of atypical childhood onset CIDP with gastrointestinal and liver impairments.

Claudin-25 (CLDN-25), also known as Claudin containing domain 1, is an uncharacterized claudin family member. It has less conserved amino acid sequences when compared to other claudins. It also has a very broad tissue expression profile and there is currently a lack of functional information from murine knockout models. Here, we report a de novo missense heterozygous variant in CLDN25 (c. 745G>C, p. A249P) found in a patient diagnosed with Pelizaeus-Merzbacher-like leukodystrophy and presenting with symptoms such as delayed motor development, several episodes of tonic absent seizures and generalized dystonia. The variant protein does not localize to the cell-cell borders where it would normally be expected to be expressed. Amino acid position 249 is located 4 amino acids from the C-terminal end of the protein where most claudin family members have a conserved binding motif for the key scaffolding protein ZO-1. However, CLDN-25 does not contain this motif. Here, we show that the C-terminal end of CLDN-25 is required for its junctional localization in a ZO-1 independent manner. The A249P mutant protein as well as a deletion mutant lacking its last 5 C-terminal amino acids also failed to localize to the cell-cell border in vitro. Intriguingly, cellular knockout of CLDN25, in vitro, appeared to increase the integrity of the tight junction between 2 contacting cells, while driving highly unusual increased movement of solutes between cells. We propose that the barrier function of CLDN-25 is akin to a decoy claudin, whereby decreasing its expression in "leaky" epithelial cells and endothelial cells will drive dynamic changes in the adhesion and interaction capacity of cell-cell contact points. While it remains unclear how this de novo CLDN-25 mutant induces leukodystrophy, our findings strongly suggest that this mutation induces haploinsufficiency of CLDN-25. Elucidating the function of this uncharacterized claudin protein will lead to a better understanding of the role of claudin proteins in health and disease.

Since 2008, FOXG1 haploinsufficiency has been linked to a severe neurodevelopmental phenotype resembling Rett syndrome but with earlier onset. Most patients are unable to sit, walk, or speak. For years, FOXG1 sequencing was only prescribed in such severe cases, limiting insight into the full clinical spectrum associated with this gene. Next-generation sequencing (NGS) now enables unbiased diagnostics. Through the European Reference Network for Rare Malformation Syndromes, Intellectual and Other Neurodevelopmental Disorders, we gathered data from patients with heterozygous FOXG1 variants presenting a mild phenotype, defined as able to speak and walk independently. We also reviewed data from three previously reported patients meeting our criteria. We identified five new patients with pathogenic FOXG1 missense variants, primarily in the forkhead domain, showing varying nonspecific intellectual disability and developmental delay. These features are not typical of congenital Rett syndrome and were rarely associated with microcephaly and epilepsy. Our findings are consistent with a previous genotype-phenotype analysis by Mitter et al. suggesting the delineation of five different FOXG1 genotype groups. Milder phenotypes were associated with missense variants in the forkhead domain. This information may facilitate prognostic assessments in children carrying a FOXG1 variant and improve the interpretation of new variants identified with genomic sequencing.

Background and ObjectivesDNA 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.MethodsThe patients were identified by the French coordinating center for mitochondrial disorders (CARAMMEL), making this a large monocentric series on childhood-onset POLG deficiency.ResultsThree 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-Barr & eacute; 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.DiscussionThe 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.

ARID1B-related disorders constitute a clinical continuum, from classic Coffin-Siris syndrome to intellectual disability (ID) with or without nonspecific dysmorphic features. Here, we describe an 11-year-old boy with an ARID1B mutation whose phenotype changed from severe developmental delay and ID to a complex neurodevelopmental disorder with multidimensional impairments, including normal intelligence despite heterogeneous IQ scores, severe motor coordination disorder, oral language disorder and attention-deficit/hyperactivity disorder. Phenotypic changes occurred after early intensive remediation and paralleled the normalization of myelination impairments, as evidenced by early brain imaging.What this paper adds?This report describes a 10-year multidisciplinary follow-up of a child with an ARID1B mutation who received early intensive remediation and whose phenotype changed during development. Clinical improvement paralleled the normalization of myelination impairments. This case supports a dimensional approach for complex neurodevelopmental disorders.

We report on MRI evidence of polyradiculoneuritis in a 15-month-old undiagnosed developmentally delayed child with paralysis and absent deep-tendon reflexes of lower limbs, progressive demyelinating sensory-motor polyneuropathy on electroneuromyogram, and hyperproteinorachia mimicking Guillain-Barre syndrome (GBS). Inefficacy of usual treatment associated with psychomotor regression, generalized hypotonia, secondary gastrointestinal involvement, and hepatic cytolysis led to consider mitochondrial disease. Finally, a biallelic polymerase-gamma (POLG) mutation was identified (c.2419C>T, c.695G>A). Standard brain and spine MRI scans were normal, but post-gadolinium MRI revealed diffuse cranial nerves and cauda equina nerve root enhancement (Figure 1), unusually found in POLG mutation.(1,2)

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.

Recent studies using cell type-specific knockout mouse models have improved our understanding of the pathophysiological relevance of suppressor of lin-12-like-HMG-CoA reductase degradation 1 (SEL1L-HRD1) endoplasmic reticulum-associated (ER-associated) degradation (ERAD); however, its importance in humans remains unclear, as no disease variant has been identified. Here, we report the identification of 3 biallelic missense variants of SEL1L and HRD1 (or SYVN1) in 6 children from 3 independent families presenting with developmental delay, intellectual disability, microcephaly, facial dysmorphisms, hypotonia, and/or ataxia. These SEL1L (p.Gly585Asp, p.Met528Arg) and HRD1 (p.Pro398Leu) variants were hypomorphic and impaired ERAD function at distinct steps of ERAD, including substrate recruitment (SEL1L p.Gly585Asp), SEL1L-HRD1 complex formation (SEL1L p.Met528Arg), and HRD1 activity (HRD1 p.Pro398Leu). Our study not only provides insights into the structure-function relationship of SEL1L-HRD1 ERAD, but also establishes the importance of SEL1L-HRD1 ERAD in humans.