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Bernardo P, Cuccurullo C, Rubino M, De Vita G, Terrone G, Bilo L, Coppola A. X-Linked Epilepsies: A Narrative Review. Int J Mol Sci 2024; 25:4110. [PMID: 38612920 PMCID: PMC11012983 DOI: 10.3390/ijms25074110] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2024] [Revised: 04/03/2024] [Accepted: 04/06/2024] [Indexed: 04/14/2024] Open
Abstract
X-linked epilepsies are a heterogeneous group of epileptic conditions, which often overlap with X-linked intellectual disability. To date, various X-linked genes responsible for epilepsy syndromes and/or developmental and epileptic encephalopathies have been recognized. The electro-clinical phenotype is well described for some genes in which epilepsy represents the core symptom, while less phenotypic details have been reported for other recently identified genes. In this review, we comprehensively describe the main features of both X-linked epileptic syndromes thoroughly characterized to date (PCDH19-related DEE, CDKL5-related DEE, MECP2-related disorders), forms of epilepsy related to X-linked neuronal migration disorders (e.g., ARX, DCX, FLNA) and DEEs associated with recently recognized genes (e.g., SLC9A6, SLC35A2, SYN1, ARHGEF9, ATP6AP2, IQSEC2, NEXMIF, PIGA, ALG13, FGF13, GRIA3, SMC1A). It is often difficult to suspect an X-linked mode of transmission in an epilepsy syndrome. Indeed, different models of X-linked inheritance and modifying factors, including epigenetic regulation and X-chromosome inactivation in females, may further complicate genotype-phenotype correlations. The purpose of this work is to provide an extensive and updated narrative review of X-linked epilepsies. This review could support clinicians in the genetic diagnosis and treatment of patients with epilepsy featuring X-linked inheritance.
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Affiliation(s)
- Pia Bernardo
- Pediatric Psychiatry and Neurology Unit, Department of Neurosciences, Santobono-Pausilipon Children’s Hospital, 80129 Naples, Italy
| | - Claudia Cuccurullo
- Neurology and Stroke Unit, Ospedale del Mare Hospital, ASL Napoli 1 Centro, 80147 Naples, Italy;
| | - Marica Rubino
- Department of Neurosciences, Reproductive Sciences and Odontostomatology, University Federico II of Naples, 80131 Naples, Italy (L.B.)
| | - Gabriella De Vita
- Department of Molecular Medicine and Medical Biotechnology, University of Naples Federico II, 80131 Naples, Italy;
| | - Gaetano Terrone
- Child Neuropsychiatry Units, Department of Translational Medical Sciences, University Federico II of Naples, 80131 Naples, Italy;
| | - Leonilda Bilo
- Department of Neurosciences, Reproductive Sciences and Odontostomatology, University Federico II of Naples, 80131 Naples, Italy (L.B.)
| | - Antonietta Coppola
- Department of Neurosciences, Reproductive Sciences and Odontostomatology, University Federico II of Naples, 80131 Naples, Italy (L.B.)
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Shokhen M, Walikonis R, Uversky VN, Allbeck A, Zezelic C, Feldman D, Levy NS, Levy AP. Molecular modeling of ARF6 dysregulation caused by mutations in IQSEC2. J Biomol Struct Dyn 2024; 42:1268-1279. [PMID: 37078745 DOI: 10.1080/07391102.2023.2199085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2022] [Accepted: 03/29/2023] [Indexed: 04/21/2023]
Abstract
IQSEC2 gene mutations are associated with epilepsy, autism, and intellectual disability. The primary function IQSEC2, mediated via its Sec 7 domain, is to act as a guanine nucleotide exchange factor for ARF6. We sought to develop a molecular model, which may explain the aberrant Sec 7 activity on ARF6 of different human IQSEC2 mutations. We integrated experimental data of IQSEC2 mutants with protein structure prediction by the RaptorX server combined with molecular modeling and molecular dynamics simulations. Normally, apocalmodulin (apoCM) binds to IQSEC2 resulting in its N-terminal fragment inhibiting access of its Sec 7 domain to ARF6. An increase in Ca2+ concentration destabilizes the interaction of IQSEC2 with apoCM and removes steric hindrance of Sec 7 binding with ARF6. Mutations at amino acid residue 350 of IQSEC2 result in loss of steric hindrance of Sec 7 binding with ARF6 leading to constitutive activation of ARF6 by Sec 7. On the other hand, a mutation at amino acid residue 359 of IQSEC2 results in constitutive hindrance of Sec 7 binding to ARF6 leading to the loss of the ability of IQSEC2 to activate ARF6. These studies provide a model for dysregulation of IQSEC2 Sec 7 activity by mutant IQSEC2 proteins.Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Michael Shokhen
- Department of Chemistry, Bar Ilan University, Ramat Gan, Israel
| | - Randall Walikonis
- Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut, USA
| | - Vladimir N Uversky
- Department of Molecular Medicine and Byrd Alzheimer's Center and Research Institute, University of South Florida, Tampa, Florida, USA
| | - Amnon Allbeck
- Department of Chemistry, Bar Ilan University, Ramat Gan, Israel
| | - Camryn Zezelic
- Technion Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel
| | - Danielle Feldman
- Technion Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel
| | - Nina S Levy
- Technion Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel
| | - Andrew P Levy
- Technion Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel
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Shoubridge C, Dudding-Byth T, Pasquier L, Goel H, Yap P, Mcconnell V. IQSEC2-related encephalopathy in males due to missense variants in the PH domain. Clin Genet 2022; 102:72-77. [PMID: 35347702 PMCID: PMC9325495 DOI: 10.1111/cge.14136] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Revised: 03/25/2022] [Accepted: 03/25/2022] [Indexed: 11/29/2022]
Abstract
Pathogenic variants in IQ motif and SEC7 domain containing protein 2 (IQSEC2) gene cause a variety of neurodevelopmental disorders, with intellectual disability as a uniform feature. We report five cases, each with a novel missense variant in the pleckstrin homology (PH) domain of the IQSEC2 protein. Male patients all present with moderate to profound intellectual disability, significant delays or absent language and speech and variable seizures. We describe the phenotypic spectrum associated with missense variants in PH domain of IQSEC2, further delineating the genotype–phenotype correlation for this X‐linked gene.
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Affiliation(s)
- Cheryl Shoubridge
- Robinson Research Institute, and Adelaide Medical School, University of Adelaide, South Australia, Australia
| | | | - Laurent Pasquier
- CHU Rennes, Service de Génétique Clinique, Centre de Référence Déficiences Intellectuelles Hôpital Sud, Rennes, France
| | - Himanshu Goel
- Hunter Genetics, Waratah, New South Wales, Australia
| | - Patrick Yap
- Genetic Health Service New Zealand (Northern Hub), Auckland, New Zealand
| | - Vivienne Mcconnell
- Northern Ireland Regional Genetics Service, Belfast City Hospital, Belfast Health & Social Care Trust, Belfast, UK
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IQSEC2 mutation associated with epilepsy, intellectual disability, and autism results in hyperexcitability of patient-derived neurons and deficient synaptic transmission. Mol Psychiatry 2021; 26:7498-7508. [PMID: 34535765 PMCID: PMC8873005 DOI: 10.1038/s41380-021-01281-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/13/2020] [Revised: 07/09/2021] [Accepted: 08/24/2021] [Indexed: 12/03/2022]
Abstract
Mutations in the IQSEC2 gene are associated with drug-resistant, multifocal infantile and childhood epilepsy; autism; and severe intellectual disability (ID). We used induced pluripotent stem cell (iPSC) technology to obtain hippocampal neurons to investigate the neuropathology of IQSEC2-mediated disease. The neurons were characterized at three-time points during differentiation to assess developmental progression. We showed that immature IQSEC2 mutant dentate gyrus (DG) granule neurons were extremely hyperexcitable, exhibiting increased sodium and potassium currents compared to those of CRISPR-Cas9-corrected isogenic controls, and displayed dysregulation of genes involved in differentiation and development. Immature IQSEC2 mutant cultured neurons exhibited a marked reduction in the number of inhibitory neurons, which contributed further to hyperexcitability. As the mutant neurons aged, they became hypoexcitable, exhibiting reduced sodium and potassium currents and a reduction in the rate of synaptic and network activity, and showed dysregulation of genes involved in synaptic transmission and neuronal differentiation. Mature IQSEC2 mutant neurons were less viable than wild-type mature neurons and had reduced expression of surface AMPA receptors. Our studies provide mechanistic insights into severe infantile epilepsy and neurodevelopmental delay associated with this mutation and present a human model for studying IQSEC2 mutations in vitro.
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Nagabushana D, Chatterjee A, Kenchaiah R, Asranna A, Arunachal G, Mundlamuri RC. Response to Steroids in IQSEC2-Related Encephalopathy Presenting with Rett-Like Phenotype and Infantile Spasms. J Pediatr Genet 2020; 12:76-80. [PMID: 36684544 PMCID: PMC9848762 DOI: 10.1055/s-0040-1721371] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2020] [Accepted: 10/14/2020] [Indexed: 01/25/2023]
Abstract
Introduction IQSEC2-related encephalopathy is an X-linked childhood neurodevelopmental disorder with intellectual disability, epilepsy, and autism. This disorder is caused by a mutation in the IQSEC2 gene, the product of which plays an important role in the development of the central nervous system. Case Report We describe the symptomatology, clinical course, and management of a 17-month-old male child with a novel IQSEC2 mutation. He presented with an atypical Rett syndrome phenotype with developmental delay, autistic features, midline stereotypies, microcephaly, hypotonia and epilepsy with multiple seizure types including late-onset infantile spasms. Spasms were followed by worsening of behavior and cognition, and regression of acquired milestones. Treatment with steroids led to control of spasms and improved attention, behavior and recovery of lost motor milestone. In the past 10 months following steroid therapy, child lags in development, remains autistic with no further seizure recurrence. Conclusion IQSEC2-related encephalopathy may present with Rett atypical phenotypes and childhood spasms. In resource-limited settings, steroids may be considered for spasm remission in IQSEC2-related epileptic encephalopathy.
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Affiliation(s)
- Divya Nagabushana
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bengaluru, India
| | - Aparajita Chatterjee
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bengaluru, India
| | - Raghavendra Kenchaiah
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bengaluru, India
| | - Ajay Asranna
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bengaluru, India
| | - Gautham Arunachal
- Department of Human Genetics, National Institute of Mental Health and Neurosciences, Bengaluru, India
| | - Ravindranadh Chowdary Mundlamuri
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bengaluru, India,Address for correspondence Ravindranadh Chowdary Mundlamuri, DM Department of Neurology, National Institute of Mental Health and NeurosciencesBengaluru 560029India
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