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PurposeWilliams-Beuren syndrome (WBS) is a well-known neurodevelopmental disorder caused by a copy-number loss at the 7q11.23 locus. Although the 1.5–1.8 Mb recurrent deletion carries several genes of interest, no single gene has been identified in which pathogenic variants cause a neurodevelopmental phenotype. At this locus, GTF2I, encoding the general transcription factor II-I, has been considered as the main candidate gene for the cognitive and behavioural phenotype of WBS, based on clinical observations of cases with atypical 7q.11.23 deletions and functional studies in humans and mice.MethodsIndividuals with a neurodevelopmental disorder were identified through a multicentre collaboration using GeneMatcher and the ERN-ITHACA network. They remained undiagnosed following genome/exome sequencing. Clinical evaluations were performed in each participating centre.ResultsWe identified seven unrelated individuals with de novo variants in GTF2I (two non-sense, two splice-site, one missense, one indel and one intragenic deletion). We also identified one individual with a WBS phenotype and low GTF2I expression identified by RNA sequencing. All eight individuals presented with global developmental delay and facial dysmorphic features, with speech delay and/or autistic features in seven cases. The effect of the two splice-site variants was confirmed by RNA sequencing.ConclusionPathogenic heterozygous GTF2I variants cause a neurodevelopmental disorder characterised by global developmental delay with facial dysmorphic features, partly resembling the phenotype observed in individuals affected with WBS.

AGAP1 is an Arf1 GTPase-activating protein that regulates endolysosomal trafficking. Damaging variants have been linked to cerebral palsy and autism. We report three new cases in which individuals had microdeletion variants in AGAP1. The affected individuals had intellectual disability (3/3), autism (3/3), dystonia with axial hypotonia (1/3), abnormalities of brain maturation (1/3), growth impairment (2/3) and facial dysmorphism (2/3). We investigated mechanisms potentially underlying AGAP1 variant-mediated neurodevelopmental impairments using the Drosophila ortholog CenG1a. We discovered reduced axon terminal size, increased neuronal endosome abundance and elevated autophagy compared to those in controls. Given potential incomplete penetrance, we assessed gene–environment interactions. We found basal elevation in the phosphorylation of the integrated stress-response protein eIF2α (or eIF2A) and inability to further increase eIF2α phosphorylation with subsequent cytotoxic stressors. CenG1a-mutant flies had increased lethality from exposure to environmental insults. We propose a model wherein disruption of AGAP1 function impairs endolysosomal trafficking, chronically activating the integrated stress response and leaving AGAP1-deficient cells susceptible to a variety of second-hit cytotoxic stressors. This model may have broader applicability beyond AGAP1 in instances where both genetic and environmental insults co-occur in individuals with neurodevelopmental disorders.

Mutations in the PQBP1 gene ( polyglutamine-binding protein-1 ) are responsible for a syndromic X-linked form of neurodevelopmental disorder (XL-NDD) with intellectual disability (ID), named Renpenning syndrome. PQBP1 encodes a protein involved in transcriptional and post-transcriptional regulation of gene expression. To investigate the consequences of PQBP1 loss, we used RNA interference to knock-down (KD) PQBP1 in human neural stem cells (hNSC). We observed a decrease of cell proliferation, as well as the deregulation of the expression of 58 genes, comprising genes encoding proteins associated with neurodegenerative diseases, playing a role in mRNA regulation or involved in innate immunity. We also observed an enrichment of genes involved in other forms of NDD ( CELF2, APC2 , etc). In particular, we identified an increase of a non-canonical isoform of another XL-NDD gene, UPF3B , an actor of nonsense mRNA mediated decay (NMD). This isoform encodes a shorter protein (UPF3B_S) deprived from the domains binding NMD effectors, however no notable change in NMD was observed after PQBP1 -KD in fibroblasts containing a premature termination codon. We showed that short non-canonical and long canonical UPF3B isoforms have different interactomes, suggesting they could play distinct roles. The link between PQBP1 loss and increase of UPF3B_S expression was confirmed in mRNA obtained from patients with pathogenic variants in PQBP1 , particularly pronounced for truncating variants and missense variants located in the C-terminal domain. We therefore used it as a molecular marker of Renpenning syndrome, to test the pathogenicity of variants of uncertain clinical significance identified in PQPB1 in individuals with NDD, using patient blood mRNA and HeLa cells expressing wild-type or mutant PQBP1 cDNA. We showed that these different approaches were efficient to prove a functional effect of variants in the C-terminal domain of the protein. In conclusion, our study provided information on the pathological mechanisms involved in Renpenning syndrome, but also allowed the identification of a biomarker of PQBP1 deficiency useful to test variant effect.

Pathogenic variants of the myelin transcription factor-1 like (MYT1L) gene include heterozygous missense, truncating variants and 2p25.3 microdeletions and cause a syndromic neurodevelopmental disorder (OMIM#616,521). Despite enrichment in de novo mutations in several developmental disorders and autism studies, the data on clinical characteristics and genotype–phenotype correlations are scarce, with only 22 patients with single nucleotide pathogenic variants reported. We aimed to further characterize this disorder at both the clinical and molecular levels by gathering a large series of patients with MYT1L-associated neurodevelopmental disorder. We collected genetic information on 40 unreported patients with likely pathogenic/pathogenic MYT1L variants and performed a comprehensive review of published data (total = 62 patients). We confirm that the main phenotypic features of the MYT1L-related disorder are developmental delay with language delay (95%), intellectual disability (ID, 70%), overweight or obesity (58%), behavioral disorders (98%) and epilepsy (23%). We highlight novel clinical characteristics, such as learning disabilities without ID (30%) and feeding difficulties during infancy (18%). We further describe the varied dysmorphic features (67%) and present the changes in weight over time of 27 patients. We show that patients harboring highly clustered missense variants in the 2–3-ZNF domains are not clinically distinguishable from patients with truncating variants. We provide an updated overview of clinical and genetic data of the MYT1L-associated neurodevelopmental disorder, hence improving diagnosis and clinical management of these patients.

CHARGE syndrome is a rare genetic disease characterized by numerous congenital abnormalities, mainly caused by de novo alterations of the CHD7 gene. It encodes a chromodomain protein, involved in the ATP-dependent remodeling of chromatin. The vast majority of CHD7 alterations consists in null alleles like deletions, nonsense substitutions or frameshift-causing variations. The aim of this study was to develop a biological test of CHD7 protein, to study the impact upon protein functionality of rare allelic variants in the CHD7 gene that elicits changes in the amino acid sequence. Using an expression vector encoding CHD7, three amino acid substitutions and one five-amino acid insertion were generated via site-directed mutagenesis. Then CHD7 proteins, either wild-type (WT) or variants, were overexpressed in HeLa cell line. Protein expression was highlighted by western blot and immunofluorescence. We then used real-time RT-PCR to study CHD7 functionality by evaluating the transcript amounts of five genes whose expression is regulated by CHD7 according to the literature. These reporter genes are 45S rDNA, SOX4, SOX10, ID2, and MYRF. We observed that, upon WT-CHD7 expression, the reporter gene transcriptions were downregulated, whereas the four variant alleles of CHD7 had no impact. This suggests that these alleles are not polymorphisms because the variant proteins appeared nonfunctional. Therefore, these variations can be considered as disease-causing of CHARGE syndrome.

Background Behavioral problems are an important issue for people with CHARGE syndrome. The similarity of their behavioral traits with those of people with autism raises questions. In a large national cross-sectional study, we used specific standardized tools for diagnosing autism (Autism Diagnostic Interview-Revised and Diagnostic and Statistical Manual of Mental Disorders, 5th edition, DSM-5) and evaluating behavioral disorders (Developmental Behavior Checklist-Parents, DBC-P) to investigate a series of individuals with CHARGE syndrome, defined by Verloes’s criteria. We evaluated their adaptive functioning level and sensory particularities and extracted several data items from medical files to assess as potential risk factors for autism and/or behavioral disorders. Results We investigated 64 individuals with CHARGE syndrome (35 females; mean age 10.7 years, SD 7.1 years). Among 46 participants with complete results for the Autism Diagnostic Interview-Revised (ADI-R), 13 (28%) had a diagnosis of autism according to the ADI-R, and 25 (54%) had a diagnosis of autism spectrum disorder (ASD) according to the DSM-5 criteria. The frequency of autistic traits in the entire group was a continuum. We did not identify any risk factor for ASD but found a negative correlation between the ADI-R score and adaptive functioning level. Among 48 participants with data for the DBC-P, 26 (55%) had behavioral disorders, which were more frequent in patients with radiological brain anomalies, impaired adaptive functioning, later independent walking, and more sensory particularities. Conclusions ASD should be considered to be an independent risk requiring early screening and management in children born with CHARGE syndrome.

RNA-binding proteins play a key role in post-transcriptional events, such as mRNA splicing, transport, stability, translation and decay. Dysregulation of RNA life can have dramatic consequences. CELF RNA-binding proteins appear to be essential during embryo development. In this study, we identified 15 patients with heterozygous missense or loss-of-function variants in the CELF4 gene by exome or genome sequencing. All variants affecting the N-terminus of the protein are essential and sufficient for the RNA-binding and splicing activity or RRM domains. Most patients presented with neurodevelopmental disorders including global developmental delay/intellectual disability (11/14), seizures (9/15) and overweight/obesity (10/14) that began in childhood. Clinical features are similar to the reported celf4-mouse mutant phenotype. This study highlights the essential role of CELF4 in development and its involvement as a novel etiology of neurodevelopmental disorders with obesity.

CHARGE syndrome is a rare genetic disorder mainly due to de novo and private truncating mutations of CHD7 gene. Here we report an intriguing hot spot of intronic mutations (c.5405-7G > A, c.5405-13G > A, c.5405-17G > A and c.5405-18C > A) located in CHD7 IVS25. Combining computational in silico analysis, experimental branch-point determination and in vitro minigene assays, our study explains this mutation hot spot by a particular genomic context, including the weakness of the IVS25 natural acceptor-site and an unconventional lariat sequence localized outside the common 40 bp upstream the acceptor splice site. For each of the mutations reported here, bioinformatic tools indicated a newly created 3’ splice site, of which the existence was confirmed using pSpliceExpress, an easy-to-use and reliable splicing reporter tool. Our study emphasizes the idea that combining these two complementary approaches could increase the efficiency of routine molecular diagnosis.

Sex chromosome aneuploidies (SCA) is a group of conditions in which individuals have an abnormal number of sex chromosomes. SCA, such as Klinefelter's syndrome, XYY syndrome, and Triple X syndrome are associated with a large range of neurological outcome. Another genetic event such as another cytogenetic abnormality may explain a part of this variable expressivity. In this study, we have recruited fourteen patients with intellectual disability or developmental delay carrying SCA associated with a copy-number variant (CNV). In our cohort (four patients 47,XXY, four patients 47,XXX, and six patients 47,XYY), seven patients were carrying a pathogenic CNV, two a likely pathogenic CNV and five a variant of uncertain significance. Our analysis suggests that CNV might be considered as an additional independent genetic factor for intellectual disability and developmental delay for patients with SCA and neurodevelopmental disorder.

RAS/MAPK pathway germline mutations were described in Rasopathies, a class of rare genetic syndromes combining facial abnormalities, heart defects, short stature, skin and genital abnormalities, and mental retardation. The majority of the mutations identified in the Rasopathies are point mutations which increase RAS/MAPK pathway signaling. Duplications encompassing RAS/MAPK pathway genes ( PTPN11 , RAF1 , MEK2 , or SHOC2 ) were more rarely described. Here we report, a syndromic familial case of a 12p duplication encompassing the dosage sensitive gene KRAS , whose phenotype overlapped with rasopathies. The patient was referred because of a history of mild learning disabilities, small size, facial dysmorphy, and pigmentation abnormalities (café-au-lait and achromic spots, and axillar lentigines). This phenotype was reminiscent of rasopathies. No mutation was identified in the most common genes associated with Noonan, cardio-facio-cutaneous, Legius, and Costello syndromes, as well as neurofibromatosis type 1. The patient constitutional DNA exhibited a ~10.5 Mb duplication at 12p, including the KRAS gene. The index case’s mother carried the same chromosome abnormality and also showed development delay with short stature, and numerous café-au-lait spots. Duplication of the KRAS gene may participate in the propositus phenotype, in particular of the specific pigmentation abnormalities. Array-CGH or some other assessment of gene/exon CNVs of RAS/MAPK pathway genes should be considered in the evaluation of individuals with rasopathies.