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Radial glia (RG) are the main progenitor cell type in the developing cortex. These cells are highly polarized, with a long basal process spanning the entire thickness of the cortex and acting as a support for neuronal migration. The RG cell terminates by an endfoot that contacts the pial (basal) surface. A shorter apical process also terminates with an endfoot that faces the ventricle, with a primary cilium protruding in the cerebrospinal fluid. These cell domains have particular subcellular compositions that are critical for the correct functioning of RG. When altered, this can affect proper development of the cortex, ultimately leading to cortical malformations, associated with different pathological outcomes. In this review, we focus on the current knowledge concerning the cell biology of these bipolar stem cells and discuss the role of their polarity in health and disease. [ABSTRACT FROM AUTHOR]

Radial glia (RG) are the main progenitor cell type in the developing cortex. These cells are highly polarized, with a long basal process spanning the entire thickness of the cortex and acting as a support for neuronal migration. The RG cell terminates by an endfoot that contacts the pial (basal) surface. A shorter apical process also terminates with an endfoot that faces the ventricle, with a primary cilium protruding in the cerebrospinal fluid. These cell domains have particular subcellular compositions that are critical for the correct functioning of RG. When altered, this can affect proper development of the cortex, ultimately leading to cortical malformations, associated with different pathological outcomes. In this review, we focus on the current knowledge concerning the cell biology of these bipolar stem cells and discuss the role of their polarity in health and disease.

Microtubules play a central role in cytoskeletal changes during neuronal development and maintenance. Microtubule dynamics is essential to polarity and shape transitions underlying neural cell division, differentiation, motility, and maturation. Kinesin superfamily protein 2A is a member of human kinesin 13 gene family of proteins that depolymerize and destabilize microtubules. In dividing cells, kinesin superfamily protein 2A is involved in mitotic progression, spindle assembly, and chromosome segregation. In postmitotic neurons, it is required for axon/dendrite specification and extension, neuronal migration, connectivity, and survival. Humans with kinesin superfamily protein 2A mutations suffer from a variety of malformations of cortical development, epilepsy, autism spectrum disorder, and neurodegeneration. In this review, we discuss how kinesin superfamily protein 2A regulates neuronal development and function, and how its deregulation causes neurodevelopmental and neurological disorders.

De novo somatic (post-zygotic) gene mutations affecting neuroglial progenitor cell types in embryonic cerebral cortex are increasingly identified in patients with drug resistant epilepsy (DRE) associated with malformations of cortical development, in particular, focal cortical dysplasias (FCD). Somatic variants in at least 16 genes have been linked to FCD type II, all encoding components of the mechanistic target of rapamycin (mTOR) pathway. FCD type II is characterized histopathologically by cytomegalic dysmorphic neurons and balloon cells. In contrast, the molecular pathogenesis of FCD I subtypes is less well understood, and histological features are characterized by alterations in columnar or laminar organization without cytomegalic dysmorphic neurons or balloon cells. In 2018, we reported somatic mutations in Solute Carrier Family 35 member A2 (SLC35A2) linked to DRE underlying FCD type I and subsequently to a new histopathological phenotype: excess oligodendrocytes and heterotopic neurons in subcortical white matter known as MOGHE (mild malformation of cortical development with oligodendroglial hyperplasia). These discoveries opened the door to studies linking somatic mutations to FCD. In this review, we discuss the biology of SLC35A2 somatic mutations in epilepsy in FCD and MOGHE, and insights into SLC35A2 epilepsy pathogenesis, describing progress to date and critical areas for investigation.

Tubulins are the highly conserved subunit of microtubules which involve in various fundamental functions including brain development. Microtubules help in neuronal proliferation, migration, differentiation, cargo transport along the axons, synapse formation, and many more. Tubulin gene family consisting of multiple isotypes, their differential expression and varied post translational modifications create a whole new level of complexity and diversity in accomplishing manifold neuronal functions. The studies on the relation between tubulin genes and brain development opened a new avenue to understand the role of each tubulin isotype in neurodevelopment. Mutations in tubulin genes are reported to cause brain development defects especially cortical malformations, referred as tubulinopathies. There is an increased need to understand the molecular correlation between various tubulin mutations and the associated brain pathology. Recently, mutations in tubulin isotypes (TUBA1A, TUBB, TUBB1, TUBB2A, TUBB2B, TUBB3, and TUBG1) have been linked to cause various neurodevelopmental defects like lissencephaly, microcephaly, cortical dysplasia, polymicrogyria, schizencephaly, subcortical band heterotopia, periventricular heterotopia, corpus callosum agenesis, and cerebellar hypoplasia. This review summarizes on the microtubule dynamics, their role in neurodevelopment, tubulin isotypes, post translational modifications, and the role of tubulin mutations in causing specific neurodevelopmental defects. A comprehensive list containing all the reported tubulin pathogenic variants associated with brain developmental defects has been prepared to give a bird's eye view on the broad range of tubulin functions. [ABSTRACT FROM AUTHOR]

Dynein heavy chain (DYNC1H1) mutations can either lead to severe cerebral cortical malformations, or alternatively may be associated with the development of spinal muscular atrophy with lower extremity predominance (SMA-LED). To assess the origin of such differences, we studied a new Dync1h1 knock-in mouse carrying the cortical malformation p.Lys3334Asn mutation. Comparing with an existing neurodegenerative Dync1h1 mutant (Legs at odd angles, Loa, p.Phe580Tyr/+), we assessed Dync1h1's roles in cortical progenitor and especially radial glia functions during embryogenesis, and assessed neuronal differentiation.p.Lys3334Asn /+ mice exhibit reduced brain and body size. Embryonic brains show increased and disorganized radial glia: interkinetic nuclear migration occurs in mutants, however there are increased basally positioned cells and abventricular mitoses. The ventricular boundary is disorganized potentially contributing to progenitor mislocalization and death. Morphologies of mitochondria and Golgi apparatus are perturbed in vitro, with different effects also in Loa mice. Perturbations of neuronal migration and layering are also observed in p.Lys3334Asn /+ mutants. Overall, we identify specific developmental effects due to a severe cortical malformation mutation in Dync1h1, highlighting the differences with a mutation known instead to primarily affect motor function.

Background: Malformations of cortical development (MCDs) can lead to peculiar neuroradiological patterns and clinical presentations (i.e., seizures, cerebral palsy, and intellectual disability) according to the specific genetic pathway of the brain development involved; and yet a certain degree of phenotypic heterogeneity exists even when the same gene is affected. Here we report a man with an malformations of cortical development extending beyond occipital lobes associated with a novel stop-gain variant in LAMC3. Case presentation: The patient is a 28-year-old man suffering from drugresistant epilepsy and moderate intellectual disability. He underwent a brain magnetic resonance imaging showing polymicrogyria involving occipital and temporal lobes bilaterally. After performing exome sequencing, a novel stopgain variant in LAMC3 (c.3871C>T; p. Arg1291*) was identified. According to the cortical alteration of the temporal regions, temporal seizures were detected; instead, the patient did not report occipital seizures. Different pharmacological and non-pharmacological interventions (i.e., vagus nerve stimulation) were unsuccessful, even though a partial seizure reduction was obtained after cenobamate administration. Conclusion: Our case report confirms that variants of a gene known to be related to specific clinical and neuroradiological pictures can unexpectedly lead to new phenotypes involving different areas of the brain. [ABSTRACT FROM AUTHOR]

Background: Malformations of cortical development (MCDs) can lead to peculiar neuroradiological patterns and clinical presentations (i.e., seizures, cerebral palsy, and intellectual disability) according to the specific genetic pathway of the brain development involved; and yet a certain degree of phenotypic heterogeneity exists even when the same gene is affected. Here we report a man with an malformations of cortical development extending beyond occipital lobes associated with a novel stop-gain variant in LAMC3.Case presentation: The patient is a 28-year-old man suffering from drug-resistant epilepsy and moderate intellectual disability. He underwent a brain magnetic resonance imaging showing polymicrogyria involving occipital and temporal lobes bilaterally. After performing exome sequencing, a novel stop-gain variant in LAMC3 (c.3871C>T; p. Arg1291*) was identified. According to the cortical alteration of the temporal regions, temporal seizures were detected; instead, the patient did not report occipital seizures. Different pharmacological and non-pharmacological interventions (i.e., vagus nerve stimulation) were unsuccessful, even though a partial seizure reduction was obtained after cenobamate administration.Conclusion: Our case report confirms that variants of a gene known to be related to specific clinical and neuroradiological pictures can unexpectedly lead to new phenotypes involving different areas of the brain.

Background: Microcephaly is a prominent feature of patients with primary autosomal recessive microcephaly 2 (MCPH2) caused by mutations in the WD Repeat Domain 62 (WDR62; OMIM: 613,583). Aim: The study aimed to identify the underlying genetic factor(s) causing microcephaly in two patients in a consanguineous Iranian family. Methods: Two male patients (11 and 27 years old) were noticed due to microcephaly, neurodevelopmental delay, and occasional seizures. The younger patient (the proband) was subjected to paired-end whole-exome sequencing followed by Sanger sequencing to detect any underlying genetic factor. Results: Upon examination, both patients showed microcephaly as a prominent manifestation; they were under-weighted as well. The patients had a moderate gross motor impairment, severe cognitive disability and speech delay, increased deep tendon reflexes, flexible joint contractures, sensorineural hearing loss, and vertical nystagmus as a new ocular finding. The proband had more severe neurodevelopmental delay symptoms. The brain magnetic resonance imaging series revealed severe structural and cortical brain abnormalities in addition to hemiatrophy. Using Whole-exome Sequencing, a novel homozygous missense variant—NM_001083961.2; c.1598A > G: p.(His533Arg)—was identified in the WDR62. Subsequently, in silico analyses determined the possible impacts of the novel variant on the structure and function of WDR62 protein. Conclusions: Herein, we identified a novel homozygous missense variant in the WDR62 in two patients with MCPH2. Vertical nystagmus and sensorineural hearing loss were detected as novel neurological findings. The present study expands the phenotype and genotype spectrum of MCPH2. [ABSTRACT FROM AUTHOR]

Mutations in nitrogen permease regulator-like 3 (NPRL3), a component of the GATOR1 complex within the mTOR pathway, are associated with epilepsy and malformations of cortical development. Little is known about the effects of NPRL3 loss on neuronal mTOR signalling and morphology, or cerebral cortical development and seizure susceptibility. We report the clinical phenotypic spectrum of a founder NPRL3 pedigree (c.349delG, p.Glu117LysFS; n = 133) among Old Order Mennonites dating to 1727. Next, as a strategy to define the role of NPRL3 in cortical development, CRISPR/Cas9 Nprl3 knockout in Neuro2a cells in vitro and in foetal mouse brain in vivo was used to assess the effects of Nprl3 knockout on mTOR activation, subcellular mTOR localization, nutrient signalling, cell morphology and aggregation, cerebral cortical cytoarchitecture and network integrity. The NPRL3 pedigree exhibited an epilepsy penetrance of 28% and heterogeneous clinical phenotypes with a range of epilepsy semiologies, i.e. focal or generalized onset, brain imaging abnormalities, i.e. polymicrogyria, focal cortical dysplasia or normal imaging, and EEG findings, e.g. focal, multi-focal or generalized spikes, focal or generalized slowing. Whole exome analysis comparing a seizure-free group (n = 37) to those with epilepsy (n = 24) to search for gene modifiers for epilepsy did not identify a unique genetic modifier that explained the variability in seizure penetrance in this cohort. Nprl3 knockout in vitro caused mTOR pathway hyperactivation, cell soma enlargement and the formation of cellular aggregates seen in time-lapse videos that were prevented with the mTOR inhibitors rapamycin or torin1. In Nprl3 knockout cells, mTOR remained localized on the lysosome in a constitutively active conformation, as evidenced by phosphorylation of ribosomal S6 and 4E-BP1 proteins, even under nutrient starvation (amino acid-free) conditions, demonstrating that Nprl3 loss decouples mTOR activation from neuronal metabolic state. To model human malformations of cortical development associated with NPRL3 variants, we created a focal Nprl3 knockout in foetal mouse cortex by in utero electroporation and found altered cortical lamination and white matter heterotopic neurons, effects which were prevented with rapamycin treatment. EEG recordings showed network hyperexcitability and reduced seizure threshold to pentylenetetrazol treatment. NPRL3 variants are linked to a highly variable clinical phenotype which we propose results from mTOR-dependent effects on cell structure, cortical development and network organization. [ABSTRACT FROM AUTHOR]

Corticogenesis is an intricate process controlled temporally and spatially by many intrinsic and extrinsic factors. Alterations during this important process can lead to severe cortical malformations. Apical neuronal progenitors are essential cells able to self-amplify and also generate basal progenitors and/or neurons. Apical radial glia (aRG) are neuronal progenitors with a unique morphology. They have a long basal process acting as a support for neuronal migration to the cortical plate and a short apical process directed towards the ventricle from which protrudes a primary cilium. This antenna-like structure allows aRG to sense cues from the embryonic cerebrospinal fluid (eCSF) helping to maintain cell shape and to influence several key functions of aRG such as proliferation and differentiation. Centrosomes, major microtubule organising centres, are crucial for cilia formation. In this review, we focus on how primary cilia influence aRG function during cortical development and pathologies which may arise due to defects in this structure. Reporting and cataloguing a number of ciliary mutant models, we discuss the importance of primary cilia for aRG function and cortical development. [ABSTRACT FROM AUTHOR]

The variety in the display of animals' cognition, emotions, and behaviors, typical of humans, has its roots within the anterior-most part of the brain: the forebrain, giving rise to the neocortex in mammals. Our understanding of cellular and molecular events instructing the development of this domain and its multiple adaptations within the vertebrate lineage has progressed in the last decade. Expanding and detailing the available knowledge on regionalization, progenitors' behavior and functional sophistication of the forebrain derivatives is also key to generating informative models to improve our characterization of heterogeneous and mechanistically unexplored cortical malformations. Classical and emerging mammalian models are irreplaceable to accurately elucidate mechanisms of stem cells expansion and impairments of cortex development. Nevertheless, alternative systems, allowing a considerable reduction of the burden associated with animal experimentation, are gaining popularity to dissect basic strategies of neural stem cells biology and morphogenesis in health and disease and to speed up preclinical drug testing. Teleost vertebrates such as zebrafish, showing conserved core programs of forebrain development, together with patients-derived in vitro 2D and 3D models, recapitulating more accurately human neurogenesis, are now accepted within translational workflows spanning from genetic analysis to functional investigation. Here, we review the current knowledge of common and divergent mechanisms shaping the forebrain in vertebrates, and causing cortical malformations in humans. We next address the utility, benefits and limitations of whole-brain/organism-based fish models or neuronal ensembles in vitro for translational research to unravel key genes and pathological mechanisms involved in neurodevelopmental diseases. [ABSTRACT FROM AUTHOR]

The variety in the display of animals’ cognition, emotions, and behaviors, typical of humans, has its roots within the anterior-most part of the brain: the forebrain, giving rise to the neocortex in mammals. Our understanding of cellular and molecular events instructing the development of this domain and its multiple adaptations within the vertebrate lineage has progressed in the last decade. Expanding and detailing the available knowledge on regionalization, progenitors’ behavior and functional sophistication of the forebrain derivatives is also key to generating informative models to improve our characterization of heterogeneous and mechanistically unexplored cortical malformations. Classical and emerging mammalian models are irreplaceable to accurately elucidate mechanisms of stem cells expansion and impairments of cortex development. Nevertheless, alternative systems, allowing a considerable reduction of the burden associated with animal experimentation, are gaining popularity to dissect basic strategies of neural stem cells biology and morphogenesis in health and disease and to speed up preclinical drug testing. Teleost vertebrates such as zebrafish, showing conserved core programs of forebrain development, together with patients-derived in vitro 2D and 3D models, recapitulating more accurately human neurogenesis, are now accepted within translational workflows spanning from genetic analysis to functional investigation. Here, we review the current knowledge of common and divergent mechanisms shaping the forebrain in vertebrates, and causing cortical malformations in humans. We next address the utility, benefits and limitations of whole-brain/organism-based fish models or neuronal ensembles in vitro for translational research to unravel key genes and pathological mechanisms involved in neurodevelopmental diseases.

The role of PI3K/AKT/mTOR pathway hyperactivation in localized brain overgrowth is evolving. We describe two patients with focal cortical dysplasia (FCD) who demonstrated somatic mutations in TSC1 and TSC2 genes in the dysplastic brain tissue but not peripheral blood. Paired whole-exome sequencing was performed on genomic DNA extracted from blood and excised brain tissue in two children with FCD who underwent excision of dysplastic tissue. Patient 1, a 14-year boy, had drug-resistant focal epilepsy with onset at 20 months. His brain MRI showed abnormalities suggestive of FCD in the left superior and middle frontal lobes. Patient 2 presented at the age of 10 years with pharmaco-resistant focal epilepsy (onset at six years). His MRI suggested FCD in the left insular lobe. Both patients underwent surgical excision of FCD, and excised tissues were pathologically confirmed to have type IIb FCD. For patient 1, a missense mutation (c.64C > T; p.Arg22Trp) was detected in the TSC1 gene in DNA of dysplastic brain tissue but not peripheral blood lymphocytes. Similarly, for patient 2, a frameshift mutation (c.4258_4261delCAGT; p.Ser1420GlyfsTer55) in the TSC2 gene was identified in the brain tissue but not blood. Both gene variants are likely pathogenic and cause mTOR pathway activation. Our report of TSC1 / TSC2 somatic mutations in patients with non-syndromic FCD suggests that localized hyperactivation of the mTOR pathway can cause focal malformations during cortical development and presents pharmacological targets for precision therapy in FCD management. [ABSTRACT FROM AUTHOR]

Dural venous sinus ectasia belongs to a rare group of venous sinus malformations of unknown origin and uncertain prognosis. We report the first patient with idiopathic congenital ectasia of the confluence of sinuses with thrombosis associated with bilateral polymicrogyria. It may highlight the causative relation between ischemia within the central nervous system due to torcular herophili ectasia with thrombosis in early pregnancy and the development of cortical malformations in neonates. We also highlight the role of MR neuroimaging in the diagnosis of these entities.

The increasing pace of gene discovery in the last decade has brought a major change in the way the genetic causes of brain malformations are being diagnosed. Unbiased genomic screening has gained the first place in the diagnostic protocol of a child with congenital (brain) anomalies and the detected variants are matched with the phenotypic presentation afterwards. This process is defined as "reverse phenotyping". Screening of DNA, through copy number variant analysis of microarrays and analysis of exome data on different platforms, obtained from the index patient and both parents has become a routine approach in many centers worldwide. Clinicians are used to multidisciplinary team interaction in patient care and disease management and this explains why the majority of research that has led to the discovery of new genetic disorders nowadays proceeds from clinical observations to genomic analysis and to data exchange facilitated by open access sharing databases. However, the relevance of multidisciplinary team interaction has not been object of systematic research in the field of brain malformations. This review will illustrate some examples of how diagnostically driven questions through multidisciplinary interaction, among clinical and preclinical disciplines, can be successful in the discovery of new genes related to brain malformations. The first example illustrates the setting of interaction among neurologists, geneticists and neuro-radiologists. The second illustrates the importance of interaction among clinical dysmorphologists for pattern recognition of syndromes with multiple congenital anomalies. The third example shows how fruitful it can be to step out of the "clinical comfort zone", and interact with basic scientists in applying emerging technologies to solve the diagnostic puzzles. • The paper reflects the opinion of the authors on the approach to the genetic research in the field of brain malformations. • Expertise from different fields, state-of -the-art technologies and interdisciplinary interaction foster advances. • Coordinated interdisciplinary approach promises to accelerate discoveries and to improve disease management. [ABSTRACT FROM AUTHOR]

Corticogenesis is an intricate process controlled temporally and spatially by many intrinsic and extrinsic factors. Alterations during this important process can lead to severe cortical malformations. Apical neuronal progenitors are essential cells able to self-amplify and also generate basal progenitors and/or neurons. Apical radial glia (aRG) are neuronal progenitors with a unique morphology. They have a long basal process acting as a support for neuronal migration to the cortical plate and a short apical process directed towards the ventricle from which protrudes a primary cilium. This antenna-like structure allows aRG to sense cues from the embryonic cerebrospinal fluid (eCSF) helping to maintain cell shape and to influence several key functions of aRG such as proliferation and differentiation. Centrosomes, major microtubule organising centres, are crucial for cilia formation. In this review, we focus on how primary cilia influence aRG function during cortical development and pathologies which may arise due to defects in this structure. Reporting and cataloguing a number of ciliary mutant models, we discuss the importance of primary cilia for aRG function and cortical development.

Brain mosaic mutations are a major cause of refractory focal epilepsies with cortical malformations such as focal cortical dysplasia, hemimegalencephaly, malformation of cortical development with oligodendroglial hyperplasia in epilepsy, and ganglioglioma. Here, we collected cerebrospinal fluid (CSF) during epilepsy surgery to search for somatic variants in cell-free DNA (cfDNA) using targeted droplet digital polymerase chain reaction. In 3 of 12 epileptic patients with known somatic mutations previously identified in brain tissue, we here provide evidence that brain mosaicism can be detected in the CSF-derived cfDNA. These findings suggest future opportunities for detecting the mutant allele driving epilepsy in CSF. ANN NEUROL 2021;89:1248-1252. [ABSTRACT FROM AUTHOR]

Objectives: To estimate the overall frequency of epilepsy in children with congenital Zika syndrome (CZS) and describe the profile of seizures and the response rate to anti‐epileptic treatment in this group of patients. Methods: A systematic review and meta‐analysis were conducted following the Cochrane Handbook and preferred reporting items for systematic reviews and meta‐analyses (PRISMA) guidelines. PubMed/MEDLINE, Scopus, Cochrane Library, SciELO, and LILACS were searched until June 23, 2020. Observational studies that evaluated the frequency of epilepsy in children diagnosed with CZS according to international criteria were included in the study. Results: Fourteen studies evaluating 903 patients diagnosed with CZS were pooled in a meta‐analysis. All studies were conducted in Brazil, with reports published between 2016 and 2020, and included children diagnosed with CSZ from 0 to 40 months of age. The overall rate of epilepsy in children diagnosed with CZS was estimated at 60% (95% confidence interval [CI] 0.51‐0.68). The studies included in this review show that the frequency of epilepsy in patients with CSZ varies with age, with higher rates in older children. Epileptic spasms was the primary type of seizure observed in this group, followed by focal and generalized crisis. The response rate to anti‐epileptic drugs was considerably low, ranging from 20% of seizure control in the first year and 30% in the second year. Significance: Children with CZS presented a high cumulative incidence of epilepsy episodes with increased severity and a low response to anti‐epileptic therapy, which is associated with the extensive damage caused by the Zika virus on the cortical structures of patients. [ABSTRACT FROM AUTHOR]

We report the case of a Caucasian Spanish origin female who showed severe psychomotor developmental delay, hypotonia, strabismus, epilepsy, short stature, and poor verbal language development. Brain magnetic resonance imaging scans showed thickened corpus callosum, cortical malformations, and dilated and abnormal configuration of the lateral ventricles without hydrocephalus. Whole‐exome sequence uncovered a de novo variant in the microtubule associated serine/threonine kinase 1 gene (MAST1; NM_014975.3:c.1565G>A:p.(Gly522Glu)) that encodes for the MAST1. Only 12 patients have been identified worldwide with 10 different variants in this gene: six patients with mega‐corpus‐callosum syndrome with cerebellar hypoplasia and cortical malformations; two patients with microcephaly and cerebellar hypoplasia; two patients with autism, one patient with diplegia, and one patient with microcephaly and dysmorphism. Our patient shows a new phenotypic subtype defined by mega‐corpus‐callosum syndrome with cortical malformations without cerebellar hypoplasia. In conclusion, our data expand the phenotypic spectrum associated to MAST1 gene variants. [ABSTRACT FROM AUTHOR]

Objective: The microscopic review of hematoxylin‐eosin–stained images of focal cortical dysplasia type IIb and cortical tuber of tuberous sclerosis complex remains challenging. Both entities are distinct subtypes of human malformations of cortical development that share histopathological features consisting of neuronal dyslamination with dysmorphic neurons and balloon cells. We trained a convolutional neural network (CNN) to classify both entities and visualize the results. Additionally, we propose a new Web‐based deep learning application as proof of concept of how deep learning could enter the pathologic routine. Methods: A digital processing pipeline was developed for a series of 56 cases of focal cortical dysplasia type IIb and cortical tuber of tuberous sclerosis complex to obtain 4000 regions of interest and 200 000 subsamples with different zoom and rotation angles to train a neural network. Guided gradient‐weighted class activation maps (Guided Grad‐CAMs) were generated to visualize morphological features used by the CNN to distinguish both entities. Results: Our best‐performing network achieved 91% accuracy and 0.88 area under the receiver operating characteristic curve at the tile level for an unseen test set. Novel histopathologic patterns were found through the visualized Guided Grad‐CAMs. These patterns were assembled into a classification score to augment decision‐making in routine histopathology workup. This score was successfully validated by 11 expert neuropathologists and 12 nonexperts, boosting nonexperts to expert level performance. Significance: Our newly developed Web application combines the visualization of whole slide images with the possibility of deep learning–aided classification between focal cortical dysplasia IIb and tuberous sclerosis complex. This approach will help to introduce deep learning applications and visualization for the histopathologic diagnosis of rare and difficult‐to‐classify brain lesions. [ABSTRACT FROM AUTHOR]

Microtubules play a central role in cytoskeletal changes during neuronal development and maintenance. Microtubule dynamics is essential to polarity and shape transitions underlying neural cell division, differentiation, motility, and maturation. Kinesin superfamily protein 2A is a member of human kinesin 13 gene family of proteins that depolymerize and destabilize microtubules. In dividing cells, kinesin superfamily protein 2A is involved in mitotic progression, spindle assembly, and chromosome segregation. In postmitotic neurons, it is required for axon/dendrite specification and extension, neuronal migration, connectivity, and survival. Humans with kinesin superfamily protein 2A mutations suffer from a variety of malformations of cortical development, epilepsy, autism spectrum disorder, and neurodegeneration. In this review, we discuss how kinesin superfamily protein 2A regulates neuronal development and function, and how its deregulation causes neurodevelopmental and neurological disorders., Competing Interests: None

The cerebral cortex is a highly organized structure responsible for advanced cognitive functions. Its development relies on a series of steps including neural progenitor cell proliferation, neuronal migration, axonal outgrowth and brain wiring. Disruption of these steps leads to cortical malformations, often associated with intellectual disability and epilepsy. We have generated a new resource to shed further light on subcortical heterotopia, a malformation characterized by abnormal neuronal position. We describe here the generation and characterization of a knockout (KO) mouse model for Eml1, a microtubule‐associated protein showing mutations in human ribbon‐like subcortical heterotopia. As previously reported for a spontaneous mouse mutant showing a mutation in Eml1, we observe severe cortical heterotopia in the KO. We also observe abnormal progenitor cells in early corticogenesis, likely to be the origin of the defects. EML1 KO mice on the C57BL/6N genetic background also appear to present a wider phenotype than the original mouse mutant, showing additional brain anomalies, such as corpus callosum abnormalities. We compare the anatomy of male and female mice and also study heterozygote animals. This new resource will help unravel roles for Eml1 in brain development and tissue architecture, as well as the mechanisms leading to severe subcortical heterotopia. [ABSTRACT FROM AUTHOR]

De novo somatic (post-zygotic) gene mutations affecting neuroglial progenitor cell types in embryonic cerebral cortex are increasingly identified in patients with drug resistant epilepsy (DRE) associated with malformations of cortical development, in particular, focal cortical dysplasias (FCD). Somatic variants in at least 16 genes have been linked to FCD type II, all encoding components of the mechanistic target of rapamycin (mTOR) pathway. FCD type II is characterized histopathologically by cytomegalic dysmorphic neurons and balloon cells. In contrast, the molecular pathogenesis of FCD I subtypes is less well understood, and histological features are characterized by alterations in columnar or laminar organization without cytomegalic dysmorphic neurons or balloon cells. In 2018, we reported somatic mutations in Solute Carrier Family 35 member A2 (SLC35A2) linked to DRE underlying FCD type I and subsequently to a new histopathological phenotype: excess oligodendrocytes and heterotopic neurons in subcortical white matter known as MOGHE (mild malformation of cortical development with oligodendroglial hyperplasia). These discoveries opened the door to studies linking somatic mutations to FCD. In this review, we discuss the biology of SLC35A2 somatic mutations in epilepsy in FCD and MOGHE, and insights into SLC35A2 epilepsy pathogenesis, describing progress to date and critical areas for investigation. [ABSTRACT FROM AUTHOR]

Abstract Mutations in COL4A1 have been reported in schizencephaly and porencephaly combined with microbleeds or calcifications, often associated with ocular and renal abnormalities, myopathy, elevated creatine kinase levels and haemolytic anaemia. In this study, we aimed to clarify the phenotypic spectrum of COL4A1/A2 mutations in the context of cortical malformations that include schizencephaly, polymicrogyria and/or heterotopia. Methods We screened for COL4A1/A2 mutations in 9 patients with schizencephaly and/or polymicrogyria suspected to be caused by vascular disruption and leading to a cerebral haemorrhagic ischaemic event. These included 6 cases with asymmetrical or unilateral schizencephaly and/or polymicrogyria and 3 cases with bilateral schizencephaly. Results One de novo missense COL4A1 mutation (c.3715 G > A, p.(Gly1239Arg)) and two COL4A2 mutations were found, respectively in one familial case (c.4129G > A, p.(Gly1377Arg)) and one sporadic patient (c.1776+1G > A). In three other cases, COL4A1 variants of unknown significance were identified. None of our patients demonstrated neuromuscular or hematological anomalies. Brain malformations included a combination of schizencephaly, mainly asymmetrical, with porencephaly or ventriculomegaly (3/3 mutated patients). We did not observe microbleeds or microcalcifications in any of our cases, hence we do not believe that they represent a distinctive feature of COL4A1/A2 mutations. Conclusions Our study further emphasizes the need to search for both COL4A1 and COL4A2 mutations in children presenting with uni- or bilateral polymicrogyria with schizencephaly, even in the absence of intracranial microbleeds, calcification or associated systemic features. [ABSTRACT FROM AUTHOR]

Background Melatonin, which is an antioxidant and neuroprotective agent, can be an effective treatment for neurological disorders. We assessed the effect of melatonin administration on histological changes, antioxidant enzyme levels, and behavioral changes in a neonate mouse model of cortical malformation. Materials and methods Cortical malformation was induced by two injections of 15 mg/kg methylazoxymethanol (MAM) on gestational day 15 (E15). Pregnant Balb/c mice were randomly divided into the following six groups: Control (CO), Melatonin (MEL), Luzindole (LUZ), MAM, MEL + MAM1 (co-treatment), and MEL + MAM2 (pretreatment). Melatonin was intraperitoneally injected at a dose of 10 mg/kg daily (from E15 until delivery of from E6 for 20 days after delivery). On postnatal day 31, the activity and anxiety of mice were assessed by open field and elevated plus maze tests, respectively. Histopathological changes in the neonate cortex were studied using hematoxylin and eosin staining and neurofilament immunohistochemistry. Enzyme-linked immunosorbent assays were used to measure the activity of nitric oxide (NO), malondialdehyde (MDA), and antioxidant enzymes, including catalase (CAT), super oxide dismutase (SOD), and glutathione peroxidase (GPX). Results In the behavioral assessment of neonate mice, a significant increase in the crossing activity and decrease in anxiety were recorded in groups treated with MAM plus melatonin. In histological examination, heterotopic, dysmorphic, and ectopic cells, as well as dyslamination, were seen in the MAM and LUZ groups. However, these defects were attenuated in the MAM plus melatonin groups. Significant reductions were recorded in the SOD and GPX levels in the MAM and LUZ groups compared to the control, while the NO level was increased in these groups. Groups that received MAM plus melatonin showed significant increases in the levels of SOD and GPX and a significant decrease in the level of NO, compared to the MAM group. Conclusion Melatonin increased the crossing activity and decreased the anxiety in the treated mice of the neonate mouse model of cortical malformation. Histologically, the administration of exogenous melatonin in pregnant mice and their neonates had a protective effect on the cerebral cortex of neonates. Also, this effect is elicited by decreasing NO and increasing antioxidative enzymes. [ABSTRACT FROM AUTHOR]

Cerebral cortical development involves a complex series of highly regulated steps to generate the laminated structure of the adult neocortex. Neuronal migration is a key part of this process. We provide here a detailed review of cortical malformations thought to be linked to abnormal neuronal migration. We have focused on providing updated views related to perturbed mechanisms based on the wealth of genetic information currently available, as well as the study of mutant genes in animal models. We discuss mainly type 1 lissencephaly, periventricular heterotopia, type II lissencephaly and polymicrogyria. We also discuss functional classifications such as the tubulinopathies, and emphasize how modern genetics is revealing genes mutated in atypical cases, as well as unexpected genes for classical cases. A role in neuronal migration is revealed for many mutant genes, although progenitor abnormalities also predominate, depending on the disorder. We finish by describing the advantages of human in vitro cell culture models, to examine human-specific cells and transcripts, and further mention non-genetic mechanisms leading to cortical malformations. [ABSTRACT FROM AUTHOR]

The etiology of epilepsy is variable and sometimes multifactorial. Clinical course and response to treatment largely depend on the precise etiology of the seizures. Along with the electroencephalogram (EEG), neuroimaging techniques, in particular, magnetic resonance imaging (MRI), are the most important tools for determining the possible etiology of epilepsy. Over the last few years, there have been many developments in data acquisition and analysis for both morphological and functional neuroimaging of people suffering from this condition. These innovations have increased the detection of underlying structural pathologies, which have till recently been classified as “cryptogenic” epilepsy. Cryptogenic epilepsy is often refractory to anti-epileptic drug treatment. In drug-resistant patients with structural or consistent functional lesions related to the epilepsy syndrome, surgery is the only treatment that can offer a seizure-free outcome. The pre-operative detection of the underlying structural condition increases the odds of successful surgical treatment of pharmacoresistant epilepsy. This article provides a comprehensive overview of neuroimaging techniques in epilepsy, highlighting recent advances and innovations and summarizes frequent etiologies of epilepsy in order to improve the diagnosis and management of patients suffering from seizures, especially young patients and children.

Fetal infection with Zika virus (ZIKV) can lead to congenital Zika virus syndrome (cZVS), which includes cortical malformations and microcephaly. The aspects of cortical development that are affected during virus infection are unknown. Using organotypic brain slice cultures generated from embryonic mice of various ages, sites of ZIKV replication including the neocortical proliferative zone and radial columns, as well as the developing midbrain, were identified. The infected radial units are surrounded by uninfected cells undergoing apoptosis, suggesting that programmed cell death may limit viral dissemination in the brain and may constrain virus-associated injury. Therefore, a critical aspect of ZIKV-induced neuropathology may be defined by death of uninfected cells. All ZIKV isolates assayed replicated efficiently in early and midgestation cultures, and two isolates examined replicated in late-gestation tissue. Alteration of neocortical cytoarchitecture, such as disruption of the highly elongated basal processes of the radial glial progenitor cells and impairment of postmitotic neuronal migration, were also observed. These data suggest that all lineages of ZIKV tested are neurotropic, and that ZIKV infection interferes with multiple aspects of neurodevelopment that contribute to the complexity of cZVS. [ABSTRACT FROM AUTHOR]

Dynein heavy chain (DYNC1H1) mutations can either lead to severe cerebral cortical malformations, or alternatively may be associated with the development of spinal muscular atrophy with lower extremity predominance (SMA-LED). To assess the origin of such differences, we studied a new Dync1h1 knock-in mouse carrying the cortical malformation p.Lys3334Asn mutation. Comparing with an existing neurodegenerative Dync1h1 mutant (Legs at odd angles , Loa , p.Phe580Tyr/+), we assessed Dync1h1's roles in cortical progenitor and especially radial glia functions during embryogenesis, and assessed neuronal differentiation. p.Lys3334Asn /+ mice exhibit reduced brain and body size. Embryonic brains show increased and disorganized radial glia: interkinetic nuclear migration occurs in mutants, however there are increased basally positioned cells and abventricular mitoses. The ventricular boundary is disorganized potentially contributing to progenitor mislocalization and death. Morphologies of mitochondria and Golgi apparatus are perturbed in vitro , with different effects also in Loa mice. Perturbations of neuronal migration and layering are also observed in p.Lys3334Asn /+ mutants. Overall, we identify specific developmental effects due to a severe cortical malformation mutation in Dync1h1 , highlighting the differences with a mutation known instead to primarily affect motor function. [Display omitted] • Dync1h1 knock-in mouse recapitulates human cortical malformation. • Dync1h1 mutations can severely impact corticogenesis affecting progenitor cells. • Neuronal migration and cortical upper layers are perturbed in mutant mice. • Subcellular defects impact organelle organization and morphology. [ABSTRACT FROM AUTHOR]

The cerebral cortex is the site of higher human cognitive and motor functions. Histologically, it is organized into six horizontal layers, each containing unique populations of molecularly and functionally distinct excitatory projection neurons and inhibitory interneurons. The stereotyped cellular distribution of cortical neurons is crucial for the formation of functional neural circuits and it is predominantly established during embryonic development. Cortical neuron development is a multiphasic process characterized by sequential steps of neural progenitor proliferation, cell cycle exit, neuroblast migration and neuronal differentiation. This series of events requires an extensive and dynamic remodeling of the cell cytoskeleton at each step of the process. As major regulators of the cytoskeleton, the family of small Rho GTPases has been shown to play essential functions in cerebral cortex development. Here we review in vivo findings that support the contribution of Rho GTPases to cortical projection neuron development and we address their involvement in the etiology of cerebral cortex malformations.

Lissencephaly is a rare disorder due to abnormal neural migration, causing neurological impairment and clinically characterised by mental retardation and epilepsy. Any disturbance of the visual pathway can cause loss of vision. The authors describe a case of a 6-year-old boy referred to the ophthalmologist presenting poor bilateral vision. This child had no other known medical conditions, and neurological examination was completely normal. Only when a magnetic resonance imaging was made that a lissencephaly-pachygyria with band heterotopia mostly occipital was noted. Cortical defects should be considered in order to diagnosis some visual defects in children. [ABSTRACT FROM AUTHOR]

Polymicrogyria is a significant malformation of cortical development with a high incidence of epilepsy and cognitive deficits. Graph theoretic analysis is a useful approach to studying network organization in brain disorders. In this study, we used task-free functional magnetic resonance imaging ( fMRI) data from four patients with polymicrogyria and refractory epilepsy. Gray matter masks from structural MRI data were parcellated into 1,024 network nodes. Functional 'connectomes' were obtained based on fMRI time series between the parcellated network nodes; network analysis was conducted using clustering coefficient, path length, node degree, and participation coefficient. These graph metrics were compared between nodes within polymicrogyric cortex and normal brain tissue in contralateral homologous cortical regions. Polymicrogyric nodes showed significantly increased clustering coefficient and characteristic path length. This is the first study using functional connectivity analysis in polymicrogyria-our results indicate a shift toward a regular network topology in polymicrogyric nodes. Regularized network topology has been demonstrated previously in patients with focal epilepsy and during focal seizures. Thus, we postulate that these network alterations predispose to seizures and may be relevant to cognitive deficits in patients with polymicrogyria. [ABSTRACT FROM AUTHOR]

High-resolution MRI is an important tool in the diagnosis of structural epilepsy in determining the seizure initiation zones, identification of the mechanisms of epileptogenesis in predicting outcomes and preventing postoperative complications in patients. In this article we demonstrate the neuroradiological and pathohistological characteristics of the main epileptogenic substrates in children using modern classification. The first part of the article is devoted to cortical malformations as the most common epileptogenic cerebral disorders.

Objective: To study the features of diagnosing and predicting structural epilepsy in children with schizencephaly (SE) based on the analysis of clinical, electrophysiological and neuroimaging results., Material and Methods: Fifteen patients with epilepsy and SE (seven boys and eight girls), aged from 3 months to 14 years, were examined., Results: Unilateral SE was detected in ten patients (closed - in four, open - in six), bilateral open SE was detected in five patients. The predominant localization of the anomaly is in the frontal region. In 100% of cases, cognitive and motor impairments of varying severity were detected. In the study group, 11 patients (73.3%) were diagnosed with epilepsy before the age of 6 years. The clinical presentations of epilepsy in children with SE included focal seizures in ten patients (73.3%), epileptic spasms in three patients (20.0%), focal seizures with secondary generalization in five (33.3%), atonic - in one child (6.7%). Refractory epilepsy was noted in 26.7% children with SE, and the absence of positive electroencephalographic changes in 40% of children., Conclusions: The extent of structural brain damage in SE in patients with epilepsy correlates with the degree of cognitive and motor deficits. The form of epilepsy, the semiotics of epileptic seizures, and the effectiveness of antiepileptic therapy do not depend on the type of SE, but correlate with the extent of cortical disorders.