X-linked Retardation Research Articles

Opportunities for Therapeutic Modulation of O-GlcNAc.

O-Linked β-N-acetylglucosamine (O-GlcNAc) is an essential, dynamic monosaccharide post-translational modification (PTM) found on serine and threonine residues of thousands of nucleocytoplasmic proteins. The installation and removal of O-GlcNAc is controlled by a single pair of enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. Since its discovery four decades ago, O-GlcNAc has been found on diverse classes of proteins, playing important functional roles in many cellular processes. Dysregulation of O-GlcNAc homeostasis has been implicated in the pathogenesis of disease, including neurodegeneration, X-linked intellectual disability (XLID), cancer, diabetes, and immunological disorders. These foundational studies of O-GlcNAc in disease biology have motivated efforts to target O-GlcNAc therapeutically, with multiple clinical candidates under evaluation. In this review, we describe the characterization and biochemistry of OGT and OGA, cellular O-GlcNAc regulation, development of OGT and OGA inhibitors, O-GlcNAc in pathophysiology, clinical progress of O-GlcNAc modulators, and emerging opportunities for targeting O-GlcNAc. This comprehensive resource should motivate further study into O-GlcNAc function and inspire strategies for therapeutic modulation of O-GlcNAc.

SRPK3 Is Essential for Cognitive and Ocular Development in Humans and Zebrafish, Explaining X-Linked Intellectual Disability.

Intellectual disability is often the outcome of neurodevelopmental disorders and is characterized by significant impairments in intellectual and adaptive functioning. X-linked intellectual disability (XLID) is a subset of these disorders caused by genetic defects on the X chromosome, affecting about 2 out of 1,000 males. In syndromic form, it leads to a broad range of cognitive, behavioral, ocular, and physical disabilities. Employing exome or genome sequencing, here we identified 4 missense variants (c.475C > G; p.H159D, c.1373C > A; p.T458N, and c.1585G > A; p.E529K, c.953C > T; p.S318L) and a putative truncating variant (c.1413_1414del; p.Y471*) in the SRPK3 gene in 9 XLID patients from 5 unrelated families. To validate SRPK3 as a novel XLID gene, we established a knockout (KO) model of the SRPK3 orthologue in zebrafish. The 8 patients ascertained postnatally shared common clinical features including intellectual disability, agenesis of the corpus callosum, abnormal eye movement, and ataxia. A ninth case, ascertained prenatally, had a complex structural brain phenotype. Together, these data indicate a pathological role of SRPK3 in neurodevelopmental disorders. In post-fertilization day 5 larvae (free swimming stage), KO zebrafish exhibited severe deficits in eye movement and swim bladder inflation, mimicking uncontrolled ocular movement and physical clumsiness observed in human patients. In adult KO zebrafish, cerebellar agenesis and behavioral abnormalities were observed, recapitulating human phenotypes of cerebellar atrophy and intellectual disability. Overall, these results suggest a crucial role of SRPK3 in the pathogenesis of syndromic X-linked intellectual disability and provide new insights into brain development, cognitive and ocular dysfunction in both humans and zebrafish. ANN NEUROL 2024;96:914-931.

Novel Corrector for Variants of SLC6A8: A Therapeutic Opportunity for Creatine Transporter Deficiency.

Mutations in creatine transporter SLC6A8 cause creatine transporter deficiency (CTD), which is responsible for 2% of all cases of X-linked intellectual disability. CTD has no current treatments and has a high unmet medical need. Inspired by the transformational therapeutic impact of small molecule "correctors" for the treatment of cystic fibrosis, which bind to mutated versions of the CFTR ion channel to promote its trafficking to the cell surface, we sought to identify small molecules that could stabilize SLC6A8 as a potential treatment for CTD. We leveraged a novel chemoproteomic technology for ligand discovery, reactive affinity probe interaction discovery, to identify small-molecule fragments with photoaffinity handles that bind to SLC6A8 in a cellular environment. We synthesized a library of irreversible covalent analogs of these molecules to characterize in functional assays, which revealed molecules that could promote the trafficking of mutant SLC6A8 variants to the cell surface. Further medicinal chemistry was able to identify reversible drug-like small molecules that both promoted trafficking of the transporter and also rescued creatine uptake. When profiled across the 27 most prevalent SLC6A8 missense variants, we found that 10-20% of patient mutations were amenable to correction by our molecules. These results were verified in an endogenous setting using the CRISPR knock-in of selected missense alleles. We established in vivo proof-of-mechanism for correctors in a novel CTD mouse model with the P544L patient-defined variant knocked in to the SLC6A8 locus, where treatment with our orally bioavailable and brain penetrant tool corrector increased brain creatine levels in heterozygous female mice, validating correctors as a potential therapeutic approach for CTD.

Loss of PHF6 causes spontaneous seizures, enlarged brain ventricles and altered transcription in the cortex of a mouse model of the Börjeson-Forssman-Lehmann intellectual disability syndrome.

Börjeson-Forssman-Lehmann syndrome (BFLS) is an X-linked intellectual disability and endocrine disorder caused by pathogenic variants of plant homeodomain finger gene 6 (PHF6). An understanding of the role of PHF6 in vivo in the development of the mammalian nervous system is required to advance our knowledge of how PHF6 mutations cause BFLS. Here, we show that PHF6 protein levels are greatly reduced in cells derived from a subset of patients with BFLS. We report the phenotypic, anatomical, cellular and molecular characterization of the brain in males and females in two mouse models of BFLS, namely loss of Phf6 in the germline and nervous system-specific deletion of Phf6. We show that loss of PHF6 resulted in spontaneous seizures occurring via a neural intrinsic mechanism. Histological and morphological analysis revealed a significant enlargement of the lateral ventricles in adult Phf6-deficient mice, while other brain structures and cortical lamination were normal. Phf6 deficient neural precursor cells showed a reduced capacity for self-renewal and increased differentiation into neurons. Phf6 deficient cortical neurons commenced spontaneous neuronal activity prematurely suggesting precocious neuronal maturation. We show that loss of PHF6 in the foetal cortex and isolated cortical neurons predominantly caused upregulation of genes, including Reln, Nr4a2, Slc12a5, Phip and ZIC family transcription factor genes, involved in neural development and function, providing insight into the molecular effects of loss of PHF6 in the developing brain.

Exome Sequencing of Consanguineous Pashtun Families With Familial Epilepsy Reveals Causative and Candidate Variants in TSEN54, MOCS2, and OPHN1.

Next-generation sequencing is advancing in low- and middle-income countries, but accessibility remains limited. In Pakistan, many members of the Pashtun population practice familial marriage and maintain distinct socio-cultural traditions, isolating them from other ethnic groups. As a result, they may harbor genetic variants that could unveil new gene-disease associations. To investigate the genetic basis of epilepsy in the Pashtun community we recently established a collaboration between Bannu University and the University of Tuebingen. Here we report our first results of exome sequencing of four families with presumed monogenetic epilepsy and Mendelian inheritance pattern. In Family #201, we identified distinct disease-causing variants. One had a homozygous pathogenic missense variant in TSEN54 (c.919G > T, p.(Ala307Ser)), linked to Pontocerebellar Hypoplasia Type 2A. The second individual had a homozygous class IV missense variant in MOCS2 (c.226G > A, p.(Gly76Arg)) which is associated with Molybdenum cofactor deficiency. In family EP02, one affected individual carried a heterozygous class III variant in OPHN1 (c.1490G > A, p.(Arg497Gln)), related to syndromic X-linked intellectual disability with epilepsy. Our small study demonstrates the promise of next-generation sequencing in genetic epilepsies among the Pashtun population. Diagnostic next-generation sequencing should be established in Pakistan as soon as possible, and if not feasible, genetic research projects may pioneer this path.

X-Linked Intellectual Disability with NEXMIF Gene Mutation and Developmental Delay with GNAO1 Gene Mutation: Case Report

X-linked intellectual disability (XLID) is a genetically heterogeneous disorder. Currently, 162 genes linked to XLID have been found, but the cause of XLID is still unclear. While the GNAO1 gene is crucial for hypotonia, epilepsy, developmental delay, and movement disorders, the NEXMIF gene, also known as KIAA2022, has associations with XLID, autism, and epilepsy. The subject of the study, a 5-year-old girl has lots of congenital defects, including a cleft palate, anal atresia, hypotonia in her lower limbs, and thumb missing. A variety of eye abnormalities, such as scoliosis, finger malformations, and craniofacial dysmorphism. Radiological tests revealed substantial heart problems, bilateral renal hypoplasia, and brain abnormalities. She met milestones more later than her contemporaries, indicating clear developmental deficits. The NEXMIF and GNAO1 genes both include heterozygous frameshift variants that were discovered through genetic research using next-generation sequencing. The complex and varied clinical signs of XLID are shown in this case. The clinical picture is further complicated by the co-occurrence of mutations in the NEXMIF and GNAO1 genes, which emphasizes the need for an approach to offer suitable therapy solutions. Future studies are necessary to understand the complex interactions between these genes and how they affect XLID and related symptoms.

Identification of a Novel Frameshift variant of the ATRX gene: a Case Report and Review of the genotype–phenotype relationship

BackgroundX-linked intellectual disability-hypotonic facies syndrome-1 (MRXHF1) and Alpha-thalassemia X-linked intellectual disability (ATR-X) syndrome are caused by pathogenic variant in the ATRX gene, a member of the switch/sucrose non-fermentable (SWI-SNF) protein family that exhibits chromatin remodeling activity. These syndromes show a wide spectrum of clinical manifestations, such as distinctive dysmorphic features, mild-to-profound intellectual disability, motor development delay, seizures, urogenital abnormalities, and gastrointestinal disorders.Case presentation and literature reviewA 3-year-old boy from a Chinese non-consanguineous family was diagnosed with MRXHF1 by whole-exome sequencing. Comprehensive family history information was obtained. The Medline database was searched until 1st Aug 2023 for articles related to ATRX pathogenic variant. Data on gene/protein mutations and clinical symptoms were extracted. The proband showed intellectual disability, motor development delay, typical facial abnormalities, urogenital defect, behavior problems, and optical nerve dysplasia. A novel frameshift mutation c.399_400dup, (p.Leu134Cysfs*2) in the ATRX gene was the primary cause, which occurs right before the ATRXDNMT3-DNMT3L (ADD) domain of ATRX protein. Missense mutation is the most common variation type. The ADD and helicase-like domains are the most frequently affected domains. Epilepsy, congenital heart disease, urogenital defect, acoustic defect, and optical defect are more prevalent in patients with frameshift mutations compared to those with missense mutations. There are more urogenital defects with C-terminal frameshift mutations than with N-terminal frameshift mutations.ConclusionWe described a novel frameshift mutation in the ATRX gene in a patient with MRXHF1 syndrome and summarized the genotype–phenotype relationship of ATRX pathogenic variant by variation type and affected protein domain. The regulatory mechanism underlying ATRX variant requires comprehensive analysis in future studies.

Measuring Enzymatic Activity of Neurodevelopmental Disorder-Associated Deubiquitylating Enzymes via an In Vitro Ubiquitin Chain Cleavage Assay.

Neurodevelopmental disorders (NDDs) are associated with impairments in nervous system function but often remain poorly understood at the molecular level. Discrete disorders caused by single genes provide models to investigate mechanisms driving atypical neurodevelopment. Variants of genes encoding deubiquitylating enzyme (DUB) family proteins are associated with several NDDs, but there is a need to determine the pathogenic mechanisms of disorders driven by these gene variants. The impact of gene variants on DUB activity can be experimentally determined using a substrate-independent in vitro ubiquitin cleavage assay. This assay does not require knowledge of downstream substrates to directly measure catalytic activity. Here, the protocol for determining the impact of gene variants on enzymatic activity is modeled using the DUB Ubiquitin Specific Protease 27, X-linked (USP27X), which is mutated in X-linked intellectual disability 105 (XLID105). This experimental pipeline can be used to clarify the mechanisms underlying neurodevelopmental disorders driven by variants in DUB genes.

Impaired hippocampal plasticity associated with loss of recycling endosomal SLC9A6/NHE6 is ameliorated by the TrkB agonist 7,8-dihydroxyflavone

Proper maintenance of intracellular vesicular pH is essential for cargo trafficking during synaptic function and plasticity. Mutations in the SLC9A6 gene encoding the recycling endosomal pH regulator (Na+, K+)/H+ exchanger isoform 6 (NHE6) are causal for Christianson syndrome (CS), a severe form of X-linked intellectual disability. NHE6 expression is also downregulated in other neurodevelopmental and neurodegenerative disorders, such as autism spectrum disorder and Alzheimer's disease, suggesting its dysfunction could contribute more broadly to the pathophysiology of other neurological conditions. To understand how ablation of NHE6 function leads to severe learning impairments, we assessed synaptic structure, function, and cellular mechanisms of learning in a novel line of Nhe6 knockout (KO) mice expressing a plasma membrane-tethered green fluorescent protein within hippocampal neurons. We uncovered significant reductions in dendritic spines density, AMPA receptor (AMPAR) expression, and AMPAR-mediated neurotransmission in CA1 pyramidal neurons. The neurons also failed to undergo functional and structural enhancement during long-term potentiation (LTP). Significantly, the selective TrkB agonist 7,8-dihydroxyflavone restored spine density as well as functional and structural LTP in KO neurons. TrkB activation thus may act as a potential clinical intervention to ameliorate cognitive deficits in CS and other neurodegenerative disorders.

Dissecting CASK: Novel splice site variant associated with male MICPCH phenotype.

CASK (MIM#300172), encoding a calcium/calmodulin-dependent serine protein kinase, is crucial for synaptic transmission and gene regulation during neural development. Pathogenic variants of CASK are known to cause several neurodevelopmental disorders, including X-linked intellectual disability and microcephaly with pontine and cerebellar hypoplasia (MICPCH). This study introduces a novel, de novo synonymous CASK variant (NM_001367721.1: c.1737G>A, p.(Glu579=)), discovered in a male patient diagnosed with MICPCH, characterized by microcephaly, developmental delay, visual impairment, and myoclonic seizures. The variant disrupts a donor splice-site at the end of exon 18. Transcriptomic analysis of blood identified 12 different CASK transcripts secondary to the synonymous variant. Nearly one third of these transcripts were predicted to result in nonsense mediated decay or protein degradation. Protein modeling revealed structural alterations in the PDZ functional domain of CASK, due to exon 18 deletion. Our findings highlight the utility of transcriptomic analysis in demonstrating the underlying disease mechanism in neurodevelopmental disorders.

X-Linked Intellectual Disability, A Novel KDM5C Variation: A Case Report

Introduction: The Lysine Demethylase 5C gene (KDM5C), located at 11p22, is a crucial gene implicated in X-linked intellectual disability (ID), also known as Claes Jensen syndrome. Mutations in the KDM5C gene can negatively impact H3K4me2/3 modifications, leading to a significant reduction in brain-derived neurotrophic factor (BDNF) and sodium voltage-gated channel alpha subunit 2 (SCN2A), which are associated with both autistic spectrum disorder (ASD) and cognitive impairment. Case Presentation: This study presents a novel KDM5C mutation [rs1569278313, Xp.11.22 (GRCh37); c.807delC exon7/25; Pro269fs], a frameshift deletion at the N terminus in exon 7, in a 7-year-old boy with a history of hypothyroidism and left-hand polydactyly. The primary complaints included seizures, short stature, speech difficulties, restlessness, gait problems, and ID. A brain computerized tomography (CT) scan was normal, while magnetic resonance imaging (MRI) revealed bilateral cerebellar hemisphere atrophy. Multifocal epileptic discharges were observed in the electroencephalogram (EEG), and the auditory brainstem response (ABR) was unremarkable. whole exome sequencing (WES) identified a pathogenic frameshift deletion in the KDM5C gene. Conclusions: This case features a frameshift deletion in exon 7 of the KDM5C gene, manifesting as a syndromic face, short stature, and global developmental delay. Additionally, we discuss the rare KDM5C syndromic features in this patient, providing valuable insight into the pathogenicity and clinical implications of this mutation.

Variants in HCFC1 and MN1 genes causing intellectual disability in two Pakistani families

BackgroundIntellectual disability (ID) is a neurodevelopmental condition affecting around 2% of children and young adults worldwide, characterized by deficits in intellectual functioning and adaptive behavior. Genetic factors contribute to the development of ID phenotypes, including mutations and structural changes in chromosomes. Pathogenic variants in the HCFC1 gene cause X-linked mental retardation syndrome, also known as Siderius type X-linked mental retardation. The MN1 gene is necessary for palate development, and mutations in this gene result in a genetic condition called CEBALID syndrome.MethodsExome sequencing was used to identify the disease-causing variants in two affected families, A and B, from various regions of Pakistan. Affected individuals in these two families presented ID, developmental delay, and behavioral abnormalities. The validation and co-segregation analysis of the filtered variant was carried out using Sanger sequencing.ResultsIn an X-linked family A, a novel hemizygous missense variant (c.5705G > A; p.Ser1902Asn) in the HCFC1 gene (NM_005334.3) was identified, while in family B exome sequencing revealed a heterozygous nonsense variant (c.3680 G > A; p. Trp1227Ter) in exon-1 of the MN1 gene (NM_032581.4). Sanger sequencing confirmed the segregation of these variants with ID in each family.ConclusionsThe investigation of two Pakistani families revealed pathogenic genetic variants in the HCFC1 and MN1 genes, which cause ID and expand the mutational spectrum of these genes.

Effect of the OPHN1 novel variant c.1025+1 G>A on RNA splicing: insights from a minigene assay

This research analyzes the clinical data, whole-exome sequencing results, and in vitro minigene functional experiments of a child with developmental delay and intellectual disability. The male patient, aged 4, began experiencing epileptic seizures at 3 months post-birth and has shown developmental delay. Rehabilitation training was administered between the ages of one and two. There were no other significant family medical histories. Through comprehensive family exome genetic testing, a hemizygous variant in the 11th exon of the OPHN1 gene was identified in the affected child: c.1025 + 1G > A. Family segregation analysis confirmed the presence of this variant in the patient’s mother, which had not been previously reported. According to the ACMG guidelines, this variant was classified as a likely pathogenic variant. In response to this variant, an in vitro minigene functional experiment was designed and conducted, confirming that the mutation affects the normal splicing of the gene’s mRNA, resulting in a 56 bp retention on the left side of Intron 11. It was confirmed that OPHN1: c.1025 + 1G > A is the pathogenic cause of X-linked intellectual disabilities in the child, with clinical phenotypes including developmental delay and seizures.

Design of iPSC-based cell model to study the functions of the <i>UBE2A</i> gene

BACKGROUND: The UBE2A protein belongs to the E2 family of ubiquitin-binding enzymes involved in the ubiquitination of substrate proteins. UBE2A mutations lead to congenital X-linked mental retardation syndrome-type Nascimento. How UBE2A participates in the central nervous system development is still unknown. AIM: To establish a cell model based on induced pluripotent stem cells (iPSCs) to study the molecular and cellular functions of UBE2A in neurogenesis. METHODS: Using genomic CRISPR-Cas9 editing and lentiviral transduction, a cell model based on iPSCs from two healthy donors was designed. This cell model includes isogenic iPSCs with knockout and inducible hyperexpression of UBE2A. In addition, iPSCs were obtained by reprogramming peripheral blood mononuclear cells of a patient diagnosed with X-linked mental retardation of Nascimento type, which has a deletion spanning the whole UBE2A locus. RESULTS: The obtained iPSCs demonstrate an ESC-like morphology. They express pluripotent cell markers OCT4, SOX2, SSEA-4, and TRA-1-81 and have normal karyotypes. iPSCs with UBE2A knockout or hyperexpression had significantly increased nuclei size compared with the isogenic control. CONCLUSION: The developed iPSC-based cell model can be used for fundamental studies of the functions of UBE2A in neurogenesis.

Taf1 knockout is lethal in embryonic male mice and heterozygous females show weight and movement disorders.

The TATA box-binding protein-associated factor 1 (TAF1) is a ubiquitously expressed protein and the largest subunit of the basal transcription factor TFIID, which plays a key role in initiation of RNA polymerase II-dependent transcription. TAF1 missense variants in human males cause X-linked intellectual disability, a neurodevelopmental disorder, and TAF1 is dysregulated in X-linked dystonia-parkinsonism, a neurodegenerative disorder. However, this field has lacked a genetic mouse model of TAF1 disease to explore its mechanism in mammals and treatments. Here, we generated and validated a conditional cre-lox allele and the first ubiquitous Taf1 knockout mouse. We discovered that Taf1 deletion in male mice was embryonically lethal, which may explain why no null variants have been identified in humans. In the brains of Taf1 heterozygous female mice, no differences were found in gross structure, overall expression and protein localisation, suggesting extreme skewed X inactivation towards the non-mutant chromosome. Nevertheless, these female mice exhibited a significant increase in weight, weight with age, and reduced movement, suggesting that a small subset of neurons was negatively impacted by Taf1 loss. Finally, this new mouse model may be a future platform for the development of TAF1 disease therapeutics.

Clinical and genetic analysis of a child with X-linked mental retardation due to variant of SLC9A7 gene

To explore the clinical and genetic characteristics of a child with mental retardation, language and motor developmental delay and epilepsy. A child who was admitted to the First Affiliated Hospital of Zhengzhou University in March 2020 for intermittent seizures for over two months was selected as the study subject. Clinical data of the child was collected. Peripheral blood samples of the child and his parents were collected and subjected to high throughput sequencing. Candidate variants were verified by Sanger sequencing and bioinformatic analysis. The clinical manifestations of the child have included mental retardation, language and motor developmental delay, and seizures. High-throughput sequencing revealed that he has harbored a hemizygous splice site variant (NM_032591.3: c.1030-1G>C) of the SLC9A7 gene, which was inherited from his mother and unreported previously. The hemizygous splice site variant (NM_032591.3: c.1030-1G>C) of the SLC9A7 gene probably underlay the disease in this child. Above finding has provided a basis for clinical diagnosis and genetic counseling.

Unveiling a Novel THOC2 Mutation's Role in X-linked Intellectual Disability

Background: Intellectual disabilities encompass a spectrum of neurodevelopmental disorders profoundly impacting an individual's cognitive abilities, adaptive behaviors, and communication skills. This article delves into the complex challenges encountered by an individual with intellectual disability, particularly examining the interplay between cognitive limitations and speech difficulties, while presenting a case report detailing the experience of a son within a non-consanguineous family diagnosed with intellectual disability due to a new genetic defect in THOC2, thereby contributing significantly to our comprehension of THOC2-related pathogenic variants. Case presentation: A 14-year-old boy from a non-consanguineous Iranian family presented with significant challenges in academics, communication, and adaptive skills, accompanied by speech problems and exhibiting distinctive physical characteristics. The exome-sequencing analysis revealed a novel hemizygous c.1559+5A>T mutation located in intron 14 (NM_001081550.2) within the THOC2 gene in the proband. Sanger sequencing further confirmed the mother as a carrier of the mutation, although she remains in good health, while the father exhibits a normal genotype. This delineates an X-linked inheritance pattern, shedding light on the familial transmission of the identified genetic anomaly. Conclusion: The precise identification of the c.1559+5A>T splicing mutation in the THOC2 gene, achieved through exome-sequencing, conclusively diagnoses X-linked intellectual disability in our patient. This breakthrough not only unravels the molecular intricacies contributing to intellectual disability but also underscores the urgency for accurate and swift disease diagnosis.

Epilepsy phenotypes across the different age-ranges in IQSEC2-related encephalopathy: An Italian multicentre retrospective cohort study

BackgroundEpilepsy is a hallmark of IQSEC2-related encephalopathy within a phenotypic variability ranging between early onset epileptic and developmental encephalopathy and X-linked intellectual disability with epilepsy. Patients and MethodsData including demographic aspects, gene variants, seizure semiology and timing, EEG features, neuroimaging and response to therapy were retrospectively collected in patients with IQSEC2-related epilepsy referring to 8 Italian tertiary centres. ResultsThe reported cohort included 11 patients (8 males and 3 females). Mean age at the onset of epilepsy was 3.90±2.80 years. No cases were reported in the first year of life. No specific epileptic syndromes were recognized. Predominant seizure-types in the age range 12–36 months included focal onset tonic seizures with impaired awareness, myoclonic seizures, and late onset spasms. Generalized motor seizures were predominant in patients between 3 and 6 years and between 12 and 18 years while focal motor seizures with impaired awareness were the most represented types between 6 and 12 years. No patients experienced status epilepticus. EEG patterns included a delayed maturation of EEG organization, irregular focal or diffuse slow activity, multifocal or diffuse epileptiform abnormalities. No structural epileptogenic lesions were detected at MRI. Valproate, lamotrigine, clobazam, topiramate and levetiracetam were the most used antiseizure medication. Complete seizure freedom was achieved only in 2 patients. ConclusionsOnset of epilepsy after the first year of age, predominance of focal seizures with impaired awareness and generalized motor seizures, no pathognomonic underlying epileptic syndrome and infrequent occurrence of status epilepticus emerged as the main features of IQSEC2-related epilepsy phenotype.

DNA methylation analysis in patients with neurodevelopmental disorders improves variant interpretation and reveals complexity

Analysis of genomic DNA methylation by generating epigenetic signature profiles (“episignatures”) is increasingly being implemented in genetic diagnosis. Here we report our experience using episignature analysis to resolve both uncomplicated and complex cases of neurodevelopmental disorder (NDD). We analysed 97 NDDs divided into: (i) a validation cohort of 59 patients with likely pathogenic/pathogenic variants characterized by a known episignature and (ii) a test cohort of 38 patients harbouring variants of unknown significance (VUS) or unidentified variants. The expected episignature was obtained in most cases with likely pathogenic/pathogenic variants (53/59; 90%), a revealing exception being the overlapping profile of two SMARCB1 pathogenic variants with ARID1A/B:c.6200, confirmed by the overlapping clinical features. In the test cohort, five cases showed the expected episignature, including: (i) novel pathogenic variants in ARID1B and BRWD3; (ii) a deletion in ATRX causing MRXFH1 X-linked mental retardation and (iii) confirmed the clinical diagnosis of Cornelia de Lange (CdL) syndrome in mutation negative CdL patients. Episignatures analysis of the in BAF complex components revealed novel functional protein interactions and common episignatures affecting homologous residues in highly conserved paralogous proteins (SMARCA2 M856V and SMARCA4 M866V). Finally, we also found sex-dependent episignatures in X-linked disorders. Implementation of episignature profiling is still in its early days but with increasing utilization come increasing awareness of the capacity of this methodology to help resolve the complex challenges of genetic diagnoses.

Clinical features and genetic analysis of 17 Chinese pedigrees affected with X-linked intellectual disability

To analyze the clinical features and genetic etiology of 17 Chinese pedigrees affected with X-linked intellectual disability (XLID). Seventeen pedigrees affected with unexplained intellectual disability which had presented at Henan Provincial People's Hospital from May 2021 to May 2023 were selected as the study subjects. Clinical data of the probands and their pedigree members were collected. Trio-whole exome sequencing (Trio-WES), Sanger sequencing and X chromosome inactivation (XCI) analysis were carried out. Pathogenicity of candidate variants was predicted based on the guidelines from the American College of Medical Genetics and Genomics and co-segregation analysis. The 17 probands, including 9 males and 8 females with an age ranging from 0.6 to 8 years old, had all shown mental retardation and developmental delay. Fourteen variants were detected by genetic testing, which included 4 pathogenic variants (MECP2: c.502C>T, MECP2: c.916C>T/c.806delG, IQSEC2: c.1417G>T), 4 likely pathogenic variants (MECP2: c.1157_1197del/c.925C>T, KDM5C: c.2128A>T, SLC6A8: c.1631C>T) and 6 variants of uncertain significance (KLHL15: c.26G>C, PAK3: c.970A>G/c.1520G>A, GRIA3: c.2153C>G, TAF1: c.2233T>G, HUWE1: c.10301T>A). The PAK3: c.970A>G, GRIA3: c.2153C>G and TAF1: c.2233T>G variants were considered as the genetic etiology for pedigrees 12, 14 and 15 by co-segregation analysis, respectively. The proband of pedigree 13 was found to have non-random XCI (81:19). Therefore, the PAK3: c.1520G>A variant may underlie its pathogenesis. Trio-WES has attained genetic diagnosis for the 17 XLID pedigrees. Sanger sequencing and XCI assay can provide auxiliary tests for the diagnosis of XLID.