Anti-seizure gene therapy for focal cortical dysplasia.

Focal cortical dysplasias are a common subtype of malformation of cortical development, which frequently presents with a spectrum of cognitive and behavioural abnormalities as well as pharmacoresistant epilepsy. Focal cortical dysplasia type II is typically caused by somatic mutations resulting in mammalian target of rapamycin (mTOR) hyperactivity, and is the commonest pathology found in children undergoing epilepsy surgery. However, surgical resection does not always result in seizure freedom, and is often precluded by proximity to eloquent brain regions. Gene therapy is a promising potential alternative treatment and may be appropriate in cases that represent an unacceptable surgical risk. Here, we evaluated a gene therapy based on overexpression of the Kv1.1 potassium channel in a mouse model of frontal lobe focal cortical dysplasia. An engineered potassium channel (EKC) transgene was placed under control of a human promoter that biases expression towards principal neurons (CAMK2A) and packaged in an adeno-associated viral vector (AAV9). We used an established focal cortical dysplasia model generated by in utero electroporation of frontal lobe neural progenitors with a constitutively active human Ras homolog enriched in brain (RHEB) plasmid, an activator of mTOR complex 1. We characterized the model by quantifying electrocorticographic and behavioural abnormalities, both in mice developing spontaneous generalized seizures and in mice only exhibiting interictal discharges. Injection of AAV9-CAMK2A-EKC in the dysplastic region resulted in a robust decrease (∼64%) in the frequency of seizures. Despite the robust anti-epileptic effect of the treatment, there was neither an improvement nor a worsening of performance in behavioural tests sensitive to frontal lobe function. AAV9-CAMK2A-EKC had no effect on interictal discharges or behaviour in mice without generalized seizures. AAV9-CAMK2A-EKC gene therapy is a promising therapy with translational potential to treat the epileptic phenotype of mTOR-related malformations of cortical development. Cognitive and behavioural co-morbidities may, however, resist an intervention aimed at reducing circuit excitability.

The clinical, imaging, pathological and genetic landscape of bottom-of-sulcus dysplasia.

Bottom-of-sulcus dysplasia (BOSD) is increasingly recognized as a cause of drug-resistant, surgically-remediable, focal epilepsy, often in seemingly MRI-negative patients. We describe the clinical manifestations, morphological features, localization patterns and genetics of BOSD, with the aims of improving management and understanding pathogenesis. We studied 85 patients with BOSD diagnosed between 2005-2022. Presenting seizure and EEG characteristics, clinical course, genetic findings and treatment response were obtained from medical records. MRI (3 T) and 18F-FDG-PET scans were reviewed systematically for BOSD morphology and metabolism. Histopathological analysis and tissue genetic testing were performed in 64 operated patients. BOSD locations were transposed to common imaging space to study anatomical location, functional network localization and relationship to normal MTOR gene expression. All patients presented with stereotyped focal seizures with rapidly escalating frequency, prompting hospitalization in 48%. Despite 42% patients having seizure remissions, usually with sodium channel blocking medications, most eventually became drug-resistant and underwent surgery (86% seizure-free). Prior developmental delay was uncommon but intellectual, language and executive dysfunction were present in 24%, 48% and 29% when assessed preoperatively, low intellect being associated with greater epilepsy duration. BOSDs were missed on initial MRI in 68%, being ultimately recognized following repeat MRI, 18F-FDG-PET or image postprocessing. MRI features were grey-white junction blurring (100%), cortical thickening (91%), transmantle band (62%), increased cortical T1 signal (46%) and increased subcortical FLAIR signal (26%). BOSD hypometabolism was present on 18F-FDG-PET in 99%. Additional areas of cortical malformation or grey matter heterotopia were present in eight patients. BOSDs predominated in frontal and pericentral cortex and related functional networks, mostly sparing temporal and occipital cortex, and limbic and visual networks. Genetic testing yielded pathogenic mTOR pathway variants in 63% patients, including somatic MTOR variants in 47% operated patients and germline DEPDC5 or NPRL3 variants in 73% patients with familial focal epilepsy. BOSDs tended to occur in regions where the healthy brain normally shows lower MTOR expression, suggesting these regions may be more vulnerable to upregulation of MTOR activity. Consistent with the existing literature, these results highlight (i) clinical features raising suspicion of BOSD; (ii) the role of somatic and germline mTOR pathway variants in patients with sporadic and familial focal epilepsy associated with BOSD; and (iii) the role of 18F-FDG-PET alongside high-field MRI in detecting subtle BOSD. The anatomical and functional distribution of BOSDs likely explain their seizure, EEG and cognitive manifestations and may relate to relative MTOR expression.

Threshold of somatic mosaicism leading to brain dysfunction with focal epilepsy.

Somatic mosaicism in a fraction of brain cells causes neurodevelopmental disorders, including childhood intractable epilepsy. However, the threshold for somatic mosaicism leading to brain dysfunction is unknown. In this study, we induced various mosaic burdens in focal cortical dysplasia type II (FCD II) mice, featuring mTOR somatic mosaicism and spontaneous behavioral seizures. The mosaic burdens ranged from approximately 1,000 to 40,000 neurons expressing the mTOR mutant in the somatosensory (SSC) or medial prefrontal (PFC) cortex. Surprisingly, approximately 8,000 to 9,000 neurons expressing the MTOR mutant, which are extrapolated to constitute 0.08-0.09% of total cells or roughly 0.04% of variant allele frequency (VAF) in the mouse hemicortex, were sufficient to trigger epileptic seizures. The mutational burden was correlated with seizure frequency and onset, with a higher tendency for electrographic inter-ictal spikes and beta- and gamma-frequency oscillations in FCD II mice exceeding the threshold. Moreover, mutation-negative FCD II patients in deep sequencing of their bulky brain tissues revealed somatic mosaicism of the mTOR pathway genes as low as 0.07% in resected brain tissues through ultra-deep targeted sequencing (up to 20 million reads). Thus, our study suggests that extremely low levels of somatic mosaicism can contribute to brain dysfunction.

Focal cortical dysplasia II caused by brain somatic mutation of IRS-1 is associated with ERK signaling pathway activation.

Somatic mutations have been identified in 10% to 63% of focal cortical dysplasia type II samples, primarily linked to the mTOR pathway. When the causative genetic mutations are not identified, this opens the possibility of discovering new pathogenic genes or pathways that could be contributing to the condition. In our previous study, we identified a novel candidate pathogenic somatic variant of IRS-1 c.1791dupG in the brain tissue of a child with focal cortical dysplasia type II. This study further explored the variant's role in causing type II focal cortical dysplasia through in vitro overexpression in 293T and SH-SY5Y cells and in vivo evaluation via in utero electroporation in fetal brains, assessing effects on neuronal migration, morphology, and network integrity. It was found that the mutant IRS-1 variant led to hyperactivity of p-ERK, increased cell volume, and was predominantly associated with the MAPK signaling pathway. In vivo, the IRS-1 c.1791dupG variant induced abnormal neuron migration, cytomegaly, and network hyperexcitability. Notably, the ERK inhibitor GDC-0994, rather than the mTOR inhibitor rapamycin, effectively rescued the neuronal defects. This study directly highlighted the ERK signaling pathway's role in the pathogenesis of focal cortical dysplasia II and provided a new therapeutic target for cases of focal cortical dysplasia II that are not treatable by rapamycin analogs.

Mouse model of focal cortical dysplasia type II generates a wide spectrum of high-frequency activities.

High-frequency oscillations (HFOs) represent an electrographic biomarker of endogenous epileptogenicity and seizure-generating tissue that proved clinically useful in presurgical planning and delineating the resection area. In the neocortex, the clinical observations on HFOs are not sufficiently supported by experimental studies stemming from a lack of realistic neocortical epilepsy models that could provide an explanation of the pathophysiological substrates of neocortical HFOs. In this study, we explored pathological epileptiform network phenomena, particularly HFOs, in a highly realistic murine model of neocortical epilepsy due to focal cortical dysplasia (FCD) type II. FCD was induced in mice by the expression of the human pathogenic mTOR gene mutation during embryonic stages of brain development. Electrographic recordings from multiple cortical regions in freely moving animals with FCD and epilepsy demonstrated that the FCD lesion generates HFOs from all frequency ranges, i.e., gamma, ripples, and fast ripples up to 800 Hz. Gamma-ripples were recorded almost exclusively in FCD animals, while fast ripples occurred in controls as well, although at a lower rate. Gamma-ripple activity is particularly valuable for localizing the FCD lesion, surpassing the utility of fast ripples that were also observed in control animals, although at significantly lower rates. Propagating HFOs occurred outside the FCD, and the contralateral cortex also generated HFOs independently of the FCD, pointing to a wider FCD network dysfunction. Optogenetic activation of neurons carrying mTOR mutation and expressing Channelrhodopsin-2 evoked fast ripple oscillations that displayed spectral and morphological profiles analogous to spontaneous oscillations. This study brings experimental evidence that FCD type II generates pathological HFOs across all frequency bands and provides information about the spatiotemporal properties of each HFO subtype in FCD. The study shows that mutated neurons represent a functionally interconnected and active component of the FCD network, as they can induce interictal epileptiform phenomena and HFOs.

Spatial omics reveals molecular changes in focal cortical dysplasia type II.

Focal cortical dysplasia (FCD) represents a group of diverse localized cortical lesions that are highly epileptogenic and occur due to abnormal brain development caused by genetic mutations, involving the mammalian target of rapamycin (mTOR). These somatic mutations lead to mosaicism in the affected brain, posing challenges to unravel the direct and indirect functional consequences of these mutations. To comprehensively characterize the impact of mTOR mutations on the brain, we employed here a multimodal approach in a preclinical mouse model of FCD type II (Rheb), focusing on spatial omics techniques to define the proteomic and lipidomic changes. Mass Spectrometry Imaging (MSI) combined with fluorescence imaging and label free proteomics, revealed insight into the brain's lipidome and proteome within the FCD type II affected region in the mouse model. MSI visualized disrupted neuronal migration and differential lipid distribution including a reduction in sulfatides in the FCD type II-affected region, which play a role in brain myelination. MSI-guided laser capture microdissection (LMD) was conducted on FCD type II and control regions, followed by label free proteomics, revealing changes in myelination pathways by oligodendrocytes. Surgical resections of FCD type IIb and postmortem human cortex were analyzed by bulk transcriptomics to unravel the interplay between genetic mutations and molecular changes in FCD type II. Our comparative analysis of protein pathways and enriched Gene Ontology pathways related to myelination in the FCD type II-affected mouse model and human FCD type IIb transcriptomics highlights the animal model's translational value. This dual approach, including mouse model proteomics and human transcriptomics strengthens our understanding of the functional consequences arising from somatic mutations in FCD type II, as well as the identification of pathways that may be used as therapeutic strategies in the future.

Targeting the EGFR pathway: An alternative strategy for the treatment of tuberous sclerosis complex?

INTRODUCTION: Tuberous sclerosis complex (TSC) is caused by variants in TSC1/TSC2, leading to constitutive activation of the mammalian target of rapamycin (mTOR) complex 1. Therapy with everolimus has been approved for TSC, but variations in success are frequent. Recently, caudal late interneuron progenitor (CLIP) cells were identified as a common origin of the TSC brain pathologies such as subependymal giant cell astrocytomas (SEGA) and cortical tubers (CT). Further, targeting the epidermal growth factor receptor (EGFR) with afatinib, which is expressed in CLIP cells, reduces cell growth in cerebral TSC organoids. However, investigation of clinical patient-derived data is lacking. AIMS: Observation of EGFR expression in SEGA, CT and focal cortical dysplasia (FCD) 2B human brain specimen and investigation of whether its inhibition could be a potential therapeutic intervention for these patients. METHODS: Brain specimens of 23 SEGAs, 6 CTs, 20 FCD2Bs and 17 controls were analysed via immunohistochemistry to characterise EGFR expression, cell proliferation (via Mib1) and mTOR signalling. In a cell-based assay using primary patient-derived cells (CT n = 1, FCD2B n = 1 and SEGA n = 4), the effects of afatinib and everolimus on cell proliferation and cell viability were observed. RESULTS: EGFR overexpression was observed in histological sections of SEGA, CT and FCD2B patients. Both everolimus and afatinib decreased the proliferation and viability in primary SEGA, tuber and FCD2B cells. CONCLUSION: Our study demonstrates that EGFR suppression might be an effective alternative treatment option for SEGAs and tubers, as well as other mTOR-associated malformations of cortical development, including FCD2B.

[18F]SynVesT-1 and [18F]FDG quantitative PET imaging in the presurgical evaluation of MRI-negative children with focal cortical dysplasia type II.

PURPOSE: MRI-negative children with focal cortical dysplasia type II (FCD II) are one of the most challenging cases in surgical epilepsy management. We aimed to utilize quantitative positron emission tomography (QPET) analysis to complement [18F]SynVesT-1 and [18F]FDG PET imaging and facilitate the localization of epileptogenic foci in pediatric MRI-negative FCD II patients. METHODS: We prospectively enrolled 17 MRI-negative children with FCD II who underwent [18F]SynVesT-1 and [18F]FDG PET before surgical resection. The QPET scans were analyzed using statistical parametric mapping (SPM) with respect to healthy controls. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and area under the curve (AUC) of [18F]SynVesT-1 PET, [18F]FDG PET, [18F]SynVesT-1 QPET, and [18F]FDG QPET in the localization of epileptogenic foci were assessed. Additionally, we developed a multivariate prediction model based on dual trace PET/QPET assessment. RESULTS: The AUC values of [18F]FDG PET and [18F]SynVesT-1 PET were 0.861 (sensitivity = 94.1%, specificity = 78.2%, PPV = 38.1%, NPV = 98.9%) and 0.908 (sensitivity = 82.4%, specificity = 99.2%, PPV = 93.3%, NPV = 97.5%), respectively. [18F]FDG QPET showed lower sensitivity (76.5%) and NPV (96.6%) but higher specificity (95.0%) and PPV (68.4%) than visual assessment, while [18F]SynVesT-1 QPET exhibited higher sensitivity (94.1%) and NPV (99.1%) but lower specificity (97.5%) and PPV (84.2%). The multivariate prediction model had the highest AUC value (AUC = 0.996, sensitivity = 100.0%, specificity = 96.6%, PPV = 81.0%, NPV = 100%). CONCLUSIONS: The multivariate prediction model based on [18F]SynVesT-1 and [18F]FDG PET/QPET assessments holds promise in noninvasively identifying epileptogenic regions in MRI-negative children with FCD II. Furthermore, the combination of visual assessment and QPET may improve the sensitivity and specificity of diagnostic tests in localizing epileptogenic foci and achieving a preferable surgical outcome in MRI-negative FCD II.

Epilepsy with faint capillary malformation or reticulated telangiectasia associated with mosaic AKT3 pathogenic variants.

Capillary malformations (CMs) are the most common type of vascular anomalies, affecting around 0.3% of newborns. They are usually caused by somatic pathogenic variants in GNAQ or GNA11. PIK3CA and PIK3R1, part of the phosphoinositide 3-kinase-protein kinase B-mammalian target of rapamycin pathway, are mutated in fainter CMs such as diffuse CM with overgrowth and megalencephaly CM. In this study, we present two young patients with a CM-like phenotype associated with cerebral anomalies and severe epilepsy. Pathogenic variants in PIK3CA and PIK3R1, as well as GNAQ and GNA11, were absent in affected cutaneous tissue biopsies. Instead, we identified two somatic pathogenic variants in the AKT3 gene. Subsequent analysis of the DNA obtained from surgically resected brain tissue of one of the two patients confirmed the presence of the AKT3 variant. Focal cortical dysplasia was also detected in this patient. Genetic analysis thus facilitated workup to reach a precise diagnosis for these patients, associating the vascular anomaly with the neurological symptoms. This study underscores the importance of searching for additional signs and symptoms to guide the diagnostic workup, especially in cases with atypical vascular malformations. In addition, it strongly emphasizes the significance of genotype-phenotype correlation studies in guiding clinicians' informed decision-making regarding patient care.

Widespread, depth-dependent cortical microstructure alterations in pediatric focal epilepsy.

OBJECTIVE: Tissue abnormalities in focal epilepsy may extend beyond the presumed focus. The underlying pathophysiology of these broader changes is unclear, and it is not known whether they result from ongoing disease processes or treatment-related side effects, or whether they emerge earlier. Few studies have focused on the period of onset for most focal epilepsies, childhood. Fewer still have utilized quantitative magnetic resonance imaging (MRI), which may provide a more sensitive and interpretable measure of tissue microstructural change. Here, we aimed to determine common spatial modes of changes in cortical architecture in children with heterogeneous drug-resistant focal epilepsy and, secondarily, whether changes were related to disease severity. METHODS: To assess cortical microstructure, quantitative T1 and T2 relaxometry (qT1 and qT2) was measured in 43 children with drug-resistant focal epilepsy (age range = 4-18 years) and 46 typically developing children (age range = 2-18 years). We assessed depth-dependent qT1 and qT2 values across the neocortex, as well as their gradient of change across cortical depths. We also determined whether global changes seen in group analyses were driven by focal pathologies in individual patients. Finally, as a proof-of-concept, we trained a classifier using qT1 and qT2 gradient maps from patients with radiologically defined abnormalities (MRI positive) and healthy controls, and tested whether this could classify patients without reported radiological abnormalities (MRI negative). RESULTS: We uncovered depth-dependent qT1 and qT2 increases in widespread cortical areas in patients, likely representing microstructural alterations in myelin or gliosis. Changes did not correlate with disease severity measures, suggesting they may represent antecedent neurobiological alterations. Using a classifier trained with MRI-positive patients and controls, sensitivity was 71.4% at 89.4% specificity on held-out MRI-negative patients. SIGNIFICANCE: These findings suggest the presence of a potential imaging endophenotype of focal epilepsy, detectable irrespective of radiologically identified abnormalities.

The use of automated and AI-driven algorithms for the detection of hippocampal sclerosis and focal cortical dysplasia.

In drug-resistant epilepsy, magnetic resonance imaging (MRI) plays a central role in detecting lesions as it offers unmatched spatial resolution and whole-brain coverage. In addition, the last decade has witnessed continued developments in MRI-based computer-aided machine-learning techniques for improved diagnosis and prognosis. In this review, we focus on automated algorithms for the detection of hippocampal sclerosis and focal cortical dysplasia, particularly in cases deemed as MRI negative, with an emphasis on studies with histologically validated data. In addition, we discuss imaging-derived prognostic markers, including response to anti-seizure medication, post-surgical seizure outcome, and cognitive reserves. We also highlight the advantages and limitations of these approaches and discuss future directions toward person-centered care.

Identification of a mosaic MTOR variant in purified neuronal DNA in a patient with focal cortical dysplasia using a novel depth electrode harvesting technique.

OBJECTIVE: Recent studies have identified brain somatic variants as a cause of focal epilepsy. These studies relied on resected tissue from epilepsy surgery, which is not available in most patients. The use of trace tissue adherent to depth electrodes used for stereo electroencephalography (EEG) has been proposed as an alternative but is hampered by the low cell quality and contamination by nonbrain cells. Here, we use our improved depth electrode harvesting technique that purifies neuronal nuclei to achieve molecular diagnosis in a patient with focal cortical dysplasia (FCD). METHODS: Depth electrode tips were collected, pooled by brain region and seizure onset zone, and nuclei were isolated and sorted using fluorescence-activated nuclei sorting (FANS). Somatic DNA was amplified from neuronal and astrocyte nuclei using primary template amplification followed by exome sequencing of neuronal DNA from the affected pool, unaffected pool, and saliva. The identified variant was validated using droplet digital polymerase chain reaction (PCR). RESULTS: An 11-year-old male with drug-resistant genetic-structural epilepsy due to left anterior insula FCD had seizures from age 3 years. Stereo EEG confirmed seizure onset in the left anterior insula. The two anterior insula electrodes were combined as the affected pool and three frontal electrodes as the unaffected pool. FANS isolated 140 neuronal nuclei from the affected and 245 neuronal nuclei from the unaffected pool. A novel somatic missense MTOR variant (p.Leu489Met, CADD score 23.7) was identified in the affected neuronal sample. Droplet digital PCR confirmed a mosaic gradient (variant allele frequency = .78% in affected neuronal sample; variant was absent in all other samples). SIGNIFICANCE: Our findings confirm that harvesting neuronal DNA from depth electrodes followed by molecular analysis to identify brain somatic variants is feasible. Our novel method represents a significant improvement compared to the previous method by focusing the analysis on high-quality cells of the cell type of interest.

Morphometric magnetic resonance imaging (MRI) postprocessing in MRI-negative patients with first unprovoked seizure.

OBJECTIVE: The aim of the study was to evaluate the benefits of morphometric magnetic resonance imaging (MRI) postprocessing in patients presenting with a first seizure and negative MRI results and to investigate these findings in the context of the clinical and electroencephalographic data, seizure recurrence rates, and epilepsy diagnosis in these patients. METHODS: We retrospectively reviewed 97 MRI scans of patients with first unprovoked epileptic seizure and no evidence of epileptogenic lesion on clinical routine MRI. Morphometric Analysis Program (MAP; v2018), automated postprocessing software, was used to identify subtle, potentially epileptogenic lesions in the three-dimensional T1-weighted MRI data. The resulting probability maps were examined together with the conventional MRI images by a reviewer who remained blinded to the patients' clinical and electroencephalographical data. Clinical data were prospectively collected between February 2018 and May 2023. RESULTS: Among the apparently MRI-negative patients, a total of 18 of 97 (18.6%) showed cortical changes suggestive of focal cortical dysplasia. Within the population with positive MAP findings (MAP+), seizure recurrence rates were 61.1% and 66.7% at 1 and 2 years after the first unprovoked seizure, respectively. Conversely, patients with negative MAP findings (MAP-) had lower seizure recurrence rates of 27.8% and 34.2% at 1 and 2 years after the first unprovoked seizure, respectively. Patients with MAP+ findings were significantly more likely to be diagnosed with epilepsy than those patients with MAP- findings (χ2 [1, n = 97] = 14.820, p < .001, odds ratio = 21.371, 95% CI = 2.710-168.531) during a mean follow-up time of 22.51 months (SD = 16.7 months, range = 1-61 months). SIGNIFICANCE: MRI postprocessing can be a valuable tool for detecting subtle epileptogenic lesions in patients with a first seizure and negative MRI results. Patients with first seizure and MAP+ findings had high seizure recurrence rates, meeting the criteria for beginning epilepsy.

Combining magnetic resonance fingerprinting with voxel-based morphometric analysis to reduce false positives for focal cortical dysplasia detection.

OBJECTIVE: We aim to improve focal cortical dysplasia (FCD) detection by combining high-resolution, three-dimensional (3D) magnetic resonance fingerprinting (MRF) with voxel-based morphometric magnetic resonance imaging (MRI) analysis. METHODS: We included 37 patients with pharmacoresistant focal epilepsy and FCD (10 IIa, 15 IIb, 10 mild Malformation of Cortical Development [mMCD], and 2 mMCD with oligodendroglial hyperplasia and epilepsy [MOGHE]). Fifty-nine healthy controls (HCs) were also included. 3D lesion labels were manually created. Whole-brain MRF scans were obtained with 1 mm3 isotropic resolution, from which quantitative T1 and T2 maps were reconstructed. Voxel-based MRI postprocessing, implemented with the morphometric analysis program (MAP18), was performed for FCD detection using clinical T1w images, outputting clusters with voxel-wise lesion probabilities. Average MRF T1 and T2 were calculated in each cluster from MAP18 output for gray matter (GM) and white matter (WM) separately. Normalized MRF T1 and T2 were calculated by z-scores using HCs. Clusters that overlapped with the lesion labels were considered true positives (TPs); clusters with no overlap were considered false positives (FPs). Two-sample t-tests were performed to compare MRF measures between TP/FP clusters. A neural network model was trained using MRF values and cluster volume to distinguish TP/FP clusters. Ten-fold cross-validation was used to evaluate model performance at the cluster level. Leave-one-patient-out cross-validation was used to evaluate performance at the patient level. RESULTS: MRF metrics were significantly higher in TP than FP clusters, including GM T1, normalized WM T1, and normalized WM T2. The neural network model with normalized MRF measures and cluster volume as input achieved mean area under the curve (AUC) of .83, sensitivity of 82.1%, and specificity of 71.7%. This model showed superior performance over direct thresholding of MAP18 FCD probability map at both the cluster and patient levels, eliminating ≥75% FP clusters in 30% of patients and ≥50% of FP clusters in 91% of patients. SIGNIFICANCE: This pilot study suggests the efficacy of MRF for reducing FPs in FCD detection, due to its quantitative values reflecting in vivo pathological changes. © 2024 International League Against Epilepsy.

Multimodal mapping of regional brain vulnerability to focal cortical dysplasia.

Focal cortical dysplasia (FCD) type II is a highly epileptogenic developmental malformation and a common cause of surgically treated drug-resistant epilepsy. While clinical observations suggest frequent occurrence in the frontal lobe, mechanisms for such propensity remain unexplored. Here, we hypothesized that cortex-wide spatial associations of FCD distribution with cortical cytoarchitecture, gene expression and organizational axes may offer complementary insights into processes that predispose given cortical regions to harbour FCD. We mapped the cortex-wide MRI distribution of FCDs in 337 patients collected from 13 sites worldwide. We then determined its associations with (i) cytoarchitectural features using histological atlases by Von Economo and Koskinas and BigBrain; (ii) whole-brain gene expression and spatiotemporal dynamics from prenatal to adulthood stages using the Allen Human Brain Atlas and PsychENCODE BrainSpan; and (iii) macroscale developmental axes of cortical organization. FCD lesions were preferentially located in the prefrontal and fronto-limbic cortices typified by low neuron density, large soma and thick grey matter. Transcriptomic associations with FCD distribution uncovered a prenatal component related to neuroglial proliferation and differentiation, likely accounting for the dysplastic makeup, and a postnatal component related to synaptogenesis and circuit organization, possibly contributing to circuit-level hyperexcitability. FCD distribution showed a strong association with the anterior region of the antero-posterior axis derived from heritability analysis of interregional structural covariance of cortical thickness, but not with structural and functional hierarchical axes. Reliability of all results was confirmed through resampling techniques. Multimodal associations with cytoarchitecture, gene expression and axes of cortical organization indicate that prenatal neurogenesis and postnatal synaptogenesis may be key points of developmental vulnerability of the frontal lobe to FCD. Concordant with a causal role of atypical neuroglial proliferation and growth, our results indicate that FCD-vulnerable cortices display properties indicative of earlier termination of neurogenesis and initiation of cell growth. They also suggest a potential contribution of aberrant postnatal synaptogenesis and circuit development to FCD epileptogenicity.

Detection of somatic and germline pathogenic variants in adult cohort of drug-resistant focal epilepsies.

OBJECTIVE: This study investigates the prevalence of pathogenic variants in the mechanistic target of rapamycin (mTOR) pathway in surgical specimens of malformations of cortical development (MCDs) and cases with negative histology. The study also aims to evaluate the predictive value of genotype-histotype findings on the surgical outcome. METHODS: The study included patients with drug-resistant focal epilepsy who underwent epilepsy surgery. Cases were selected based on histopathological diagnosis, focusing on MCDs and negative findings. We included brain tissues both as formalin-fixed, paraffin-embedded (FFPE) or fresh frozen (FF) samples. Single-molecule molecular inversion probes (smMIPs) analysis was conducted, targeting the MTOR gene in FFPE samples and 10 genes within the mTOR pathway in FF samples. Correlations between genotype-histotype and surgical outcome were examined. RESULTS: We included 78 patients for whom we obtained 28 FFPE samples and 50 FF tissues. Seventeen pathogenic variants (22 %) were identified and validated, with 13 being somatic within the MTOR gene and 4 germlines (2 DEPDC5, 1 TSC1, 1 TSC2). Pathogenic variants in mTOR pathway genes were exclusively found in FCDII and TSC cases, with a significant association between FCD type IIb and MTOR genotype (P = 0.003). Patients carrying mutations had a slightly better surgical outcome than the overall cohort, however it results not significant. The FCDII diagnosed cases more frequently had normal neuropsychological test, a higher incidence of auras, fewer multiple seizure types, lower occurrence of seizures with awareness impairment, less ictal automatisms, fewer Stereo-EEG investigations, and a longer period long-life of seizure freedom before surgery. SIGNIFICANCE: This study confirms that somatic MTOR variants represent the primary genetic alteration detected in brain specimens from FCDII/TSC cases, while germline DEPDC5, TSC1/TSC2 variants are relatively rare. Systematic screening for these mutations in surgically treated patients' brain specimens can aid histopathological diagnoses and serve as a biomarker for positive surgical outcomes. Certain clinical features associated with pathogenic variants in mTOR pathway genes may suggest a genetic etiology in FCDII patients.

Epileptogenesis and drug-resistant in focal cortical dysplasias: Update on clinical, cellular, and molecular markers.

Focal cortical dysplasia (FCD) is a cortical malformation in brain development and is considered as one of the major causes of drug-resistant epilepsiesin children and adults. The pathogenesis of FCD is yet to be fully understood. Imaging markers such as MRI are currently the surgeons major obstacle due to the difficulty in delimiting the precise dysplasic area and a mosaic brain where there is epileptogenic tissue invisible to MRI. Also increased gene expression and activity may be responsible for the alterations in cell proliferation, migration, growth, and survival. Altered expressions were found, particularly in the PI3K/AKT/mTOR pathway. Surgery is still considered the most effective treatment option, due to drug-resistance, and up to 60 % of patients experience complete seizure control, varying according to the type and location of FCD. Both genetic and epigenetic factors may be involved in the pathogenesis of FCD, and there is no conclusive evidence whether these alterations are inherited or have an environmental origin.

Neuropsychological outcome after frontal surgery for pediatric-onset epilepsy with focal cortical dysplasia in adolescent and young adult.

OBJECTIVE: We investigated neuropsychological outcome in patients with pharmacoresistant pediatric-onset epilepsy caused by focal cortical dysplasia (FCD), who underwent frontal lobe resection during adolescence and young adulthood. METHODS: Twenty-seven patients were studied, comprising 15 patients who underwent language-dominant side resection (LDR) and 12 patients who had languagenondominant side resection (n-LDR). We evaluated intelligence (language function, arithmetic ability, working memory, processing speed, visuo-spatial reasoning), executive function, and memory in these patients before and two years after resection surgery. We analyzed the relationship between neuropsychological outcome and resected regions (side of language dominance and location). RESULTS: Although 75% of the patients showed improvement or no change in individual neuropsychological tests after surgical intervention, 25% showed decline. The cognitive tests that showed improvement or decline varied between LDR and n-LDR. In patients who had LDR, decline was observed in Vocabulary and Phonemic Fluency (both 5/15 patients), especially after resection of ventrolateral frontal cortex, and improvement was observed in WCST-Category (7/14 patients), Block Design (6/15 patients), Digit Symbol (4/15 patients), and Delayed Recall (3/9 patients). In patients who underwent n-LDR, improvement was observed in Vocabulary (3/12 patients), but decline was observed in Block Design (2/9 patients), and WCST-Category (2/9 patients) after resection of dorsolateral frontal cortex; and Arithmetic (3/10 patients) declined after resection of dorsolateral frontal cortex or ventrolateral frontal cortex. General Memory (3/8 patients), Visual Memory (3/8 patients), Delayed Recall (3/8 patients), Verbal Memory (2/9 patients), and Digit Symbol (3/12 patients) also declined after n-LDR. CONCLUSION: Postoperative changes in cognitive function varied depending on the location and side of the resection. For precise presurgical prediction of neuropsychological outcome after surgery, further prospective studies are needed to accumulate data of cognitive changes in relation to the resection site.

Focal cortical dysplasia is a frequent coexistent pathology in patients with Rasmussen's encephalitis.

INTRODUCTION: Rasmussen's encephalitis (RE) is a rare, predominantly pediatric epilepsy disorder of unknown etiology. It classically affects one of the cerebral hemispheres and histologically shows cortical chronic inflammation, gliosis, and neuronal loss. The etiopathogenesis of RE remains unknown, with genetic, infectious, and autoimmune factors all speculated to play a role. Although the histologic findings in RE are well described, few studies have investigated a large cohort of cases looking for the coexistence of RE with focal cortical dysplasia (FCD). DESIGN: The study is a retrospective review of RE patients who underwent surgical resection of brain tissue between 1979 and 2021. Relevant patient history was retrieved, and available histologic slides were reviewed. The histologic severity of RE was described according to the Pardo criteria. In cases where FCD was present, the observed patterns of FCD (namely Ia, Ib, IIa, IIb, etc.) were described using the International League Against Epilepsy (ILAE) classification. RESULTS: Thirty-eight resection specimens from 31 patients formed the study cohort. Seventeen patients (54.8 %) were male; average age at surgery was 8 years (range: 2-28 years). Twenty-seven resection specimens (71.1 %) from 23 patients (74 %) showed evidence of coexistent FCD. Most cases with FCD resembled the ILAE type Ib (n = 23) pattern. Cases of RE that did not show FCD were either Pardo stage 1 (n = 5) or 4 (n = 6), with all Pardo stage 2 and 3 cases demonstrating FCD. CONCLUSIONS: FCD was found in most patients with RE (74 %). The most observed pattern of FCD was ILAE Ib.

Analysis of predictive factors in surgical treatment of intractable epilepsy caused by focal cortical dysplasia in children.

OBJECTIVE: This study aims to analyze key factors affecting the surgical outcome of children with intractable epilepsy caused by focal cortical dysplasia, providing more effective clinical guidance. METHODS: We conducted a study from March 2019 to February 2021, selecting 80 children with intractable epilepsy caused by focal cortical dysplasia who underwent surgical treatment. Comprehensive inclusion criteria were met. We collected general information and treatment outcomes before and after surgery, with a two-year postoperative follow-up. Patients were categorized into good and poor outcome groups based on outcomes. Various factors including pathological types, age of onset, seizure frequency, and extent of resection were selected as variables. Logistic regression analysis investigated predictive factors. RESULTS: Engel class I included 53 cases, class II had 16 cases, class III had 9 cases, and class IV had 2 cases. Thus, 53 cases were in the good outcome group, and 27 in the poor outcome group. General data showed no significant differences between the groups (p > 0.05). Single-factor analysis revealed statistically significant risk factors: FCD classification, MRI results, age of onset, seizure frequency, and extent of resection (p < 0.05). Logistic multifactor analysis indicated seizure frequency. acute postoperative seizures (APSO) and extent of resection as independent influencing factors (p < 0.05). CONCLUSION: Seizure frequency, extent of resection, and APSO are key independent factors for surgical outcome in children with intractable epilepsy caused by focal cortical dysplasia. Clinicians should consider these factors when planning treatment to improve success rates and outcome, enhancing quality of life for affected children.