The recurrent pathogenic variant KCNC1-p.Ala421Val (A421V) is a cause of developmental and epileptic encephalopathy characterized by moderate-to-severe developmental delay/intellectual disability, and infantile-onset treatment-resistant epilepsy with multiple seizure types, including myoclonic seizures. Yet, the mechanistic basis of this disease, and of the KCNC1 disease spectrum, remains unclear. KCNC1 encodes Kv3.1, a voltage-gated potassium channel subunit that is strongly and selectively expressed in neurons capable of generating action potentials at high frequency, including parvalbumin-positive fast-spiking GABAergic inhibitory interneurons in cerebral cortex (PV-INs) that are known to be important for cognitive function and plasticity as well as control of network excitation to prevent seizures. In this study, we generate a novel transgenic mouse model with conditional expression of the A421V pathogenic missense variant (Kcnc1-A421V/+ mice) to explore the specific physiological mechanisms of KCNC1 developmental and epileptic encephalopathy. Our results indicate that global heterozygous expression of the A421V variant leads to cognitive impairment, epilepsy, and premature lethality. We observe decreased PV-IN cell surface expression of Kv3.1 via immunohistochemistry, decreased voltage-gated potassium current density in PV-INs using outside-out nucleated macropatch recordings in brain slice, and profound impairments in the intrinsic excitability of cerebral cortex PV-INs (but not excitatory neurons) via current-clamp electrophysiology. In vivo two-photon calcium imaging revealed altered activity in Kcnc1-A421V/+ PV-INs and excitatory cells, as well as hypersynchronous discharges correlated with brief paroxysmal movements that were subsequently shown to be myoclonic seizures on electroencephalography. We found alterations in PV-IN-mediated inhibitory neurotransmission in young adult but not juvenile Kcnc1-A421V/+ mice relative to wild-type controls. Together, these results establish the specific impact of the recurrent Kv3.1-A421V variant on neuronal excitability and synaptic physiology across development to drive network dysfunction underlying KCNC1 epileptic encephalopathy.

Hypomyelination and atrophy of basal ganglia and cerebellum (H-ABC) is a rare leukodystrophy associated with causal variants in β-tubulin 4A (TUBB4A). The recurring variant p.Asp249Asn (D249N) presents in infancy with dystonia, communication deficits, and loss of ambulation during the first decade of life. In this study, we characterized a genetic murine series (Tubb4aKO/KO, Tubb4aD249N/+, Tubb4aD249N/KO, and Tubb4aD249N/D249N) to demonstrate that disease severity correlates with the expression of mutant Tubb4a and relative preservation of wild-type tubulin. To further evaluate the translational potential of Tubb4a suppression as a therapy in H-ABC, we identified a well-tolerated Tubb4a-targeted antisense oligonucleotide (ASO) candidate that selectively reduces Tubb4a. Notably, single intracerebroventricular administration of ASO in postnatal Tubb4aD249N/KO mice drastically extends its lifespan, improves motor phenotypes, and reduces seizures. Neuropathologically, treating ASO Tubb4aD249N/KO mice prevents myelin and oligodendrocyte (OL) loss and recovers visual evoked potential latencies in vivo. Furthermore, the microtubule function of Mbp mRNA transport from the OL soma to the myelin sheath is retained. A major limitation we noted is that ASOs fail to target cerebellar granule neurons even with multiple routes of administration in the brain. This is the first preclinical proof-of-concept for Tubb4a suppression via ASO as a disease-modifying therapy for H-ABC.

About half of patients who undergo epilepsy surgery for drug-resistant epilepsy have seizure recurrence, supporting the need for approaches that more accurately identify the epileptogenic zone, defined as the brain areas whose removal causes cessation of seizures. Altered network connectivity has emerged as a candidate biomarker of the epileptogenic zone, but how connectivity is altered in the epileptogenic zone remains uncertain, with prior studies reporting inconsistent results. We hypothesized that a difference in intrinsic versus extrinsic connectivity of the epileptogenic zone may explain prior discrepant findings. We studied a multicenter cohort of adult and pediatric patients who underwent intracranial EEG recording and brain stimulation as part of epilepsy surgery planning. We measured spontaneous connectivity using Pearson correlation and perturbational connectivity using stimulation evoked potentials, modeling the connectivity according to the location of contacts in relation to the seizure onset zone (SOZ) while controlling for inter-electrode distance. We analyzed 79 patients (37 adults, 42 children). For both adult and pediatric patients, resting connectivity was higher within compared to outside the SOZ, but resting connectivity between SOZ and non-SOZ contacts was reduced. Stimulation connectivity followed a similar pattern, with elevated within-SOZ connectivity but reduced connectivity between SOZ and non-SOZ. The results support the hypothesis that the epileptogenic zone is disconnected from the rest of the brain but intrinsically hyperconnected. This result helps reconcile prior inconsistencies across studies, aligns with the results of basic science studies, and suggests that future translational work should model this heterogeneous pattern to increase the yield of using connectivity to localize the epileptogenic zone.

Pathogenic variants in GABAA receptor subunit genes (GABR*) are important contributors to rare and common genetic epilepsies. Here, we present a comprehensive analysis of variants in GABRB1, which encodes the GABAA receptor β1 subunit, by revealing their functional implications, establishing genotype-phenotype correlations and evaluating treatment response. Clinical information on individuals carrying a GABRB1 variant was obtained through an international collaboration and literature review. Our cohort included 19 individuals (7 males, 12 females) from 15 families harbouring 13 different GABRB1 variants (11 missense, 1 indel, 1 stop). Functional analysis was performed using two-electrode voltage-clamp recordings in Xenopus laevis oocytes. For all 11 missense variants, α1β1γ2 GABAA receptors with a single mutant β1 subunit were used. Four missense variants were selected for further functional analysis using α5β1γ2 GABAA receptors with two mutant β1 subunits. Gain-of-function (GoF) effects, characterized by increased GABA-sensitivity, were observed for eight missense variants. Loss-of-function (LoF) effects were observed for one variant and no functional effects for two variants. Clinically, GoF variants were only observed in individuals with severe early-onset disease, including profound intellectual disability, hypotonia and early mortality. Additionally, cortical visual impairment, dysmorphisms and cortical atrophy were exclusive to this cohort. By integrating previously reported clinical data for variants in other GABR* genes, we validated that these features were associated with GoF variants more broadly. The only LoF variant was identified in a nuclear family with the relatively milder syndrome of genetic epilepsy with febrile seizures plus. Seizures were therapy-resistant in all individuals with GoF variants and a single individual with a LoF variant. The GABAergic anti-seizure medication (ASM) vigabatrin caused life-threatening side-effects in two individuals with GoF variants, while the sodium-channel blocker (SCB) lamotrigine exacerbated seizures in a single individual carrying a LoF variant. By integrating data from literature on all GABR* variants, we observed a potential dichotomy in treatment responses: GABAergic and broad-spectrum ASMs, such as valproate and levetiracetam, were more effective for individuals with LoF variants in GABR* genes, while SCBs showed greater benefit for GoF variants. Additionally, there is an increased risk of adverse effects of SCBs in LoF and vigabatrin in GoF variants. Our results highlight the importance of functional characterization of variants and clinical predictors in guiding treatment strategies for individuals with GABRB1 and other GABR* variants, although larger prospective studies are needed to confirm these observations.

Automated seizure detection and localization from intracranial EEG requires validated benchmark datasets with expert annotations, yet existing open datasets lack multi-expert consensus annotations and exclude stimulation-induced seizures. We present stereotactic EEG recordings from 83 seizures (46 spontaneous, 37 stimulation-induced) across 32 patients (19 from the University of Pennsylvania, 13 from the Children's Hospital of Philadelphia) with drug-resistant epilepsy. Three board-certified epileptologists independently annotated each seizure for onset time, onset channels, and channels seizing at 10 seconds post-onset using a standardized protocol. Consensus annotations were determined through majority voting. Inter-rater agreement was κ = 0.64 for onset channels and κ = 0.62 for spread channels. Individual rater agreement with consensus was κ = 0.81 for onset and κ = 0.80 for spread. Agreement metrics did not differ between spontaneous and stimulation-induced seizures. All data follow Brain Imaging Data Structure (BIDS) standards and include electrode localizations, patient demographics, and clinical outcomes. This dataset enables the validation of seizure onset and spread detection and localization against human expert performance and supports comparative analysis of seizure networks across spontaneous and stimulation-induced seizures.

BACKGROUND:Epilepsy is a core feature of Angelman syndrome (AS) and a major contributor to morbidity and caregiver burden. The current study provides updated caregiver-reported data on seizure characteristics, triggers, and management in AS. METHODS:Caregivers of 130 individuals with AS enrolled in the Linking Angelman and Dup15q Data for Expanded Research Database completed an online questionnaire assessing seizure characteristics, age at first seizure and diagnosis, perceived triggers, and management strategies. Participants were grouped by molecular subtype (deletion vs nondeletion). Descriptive statistics and group comparisons were conducted. RESULTS:Seizures were more frequently reported in individuals with deletion subtypes compared to those with nondeletion subtypes. The most common seizure-related manifestations (myoclonic, atonic, and atypical absence features) did not differ between groups. Individuals with deletion subtypes experienced earlier epilepsy diagnosis than those with nondeletion subtypes, though age at first seizure prompting medical attention did not differ significantly between the groups. About half of caregivers were unsure of seizure triggers; among identified triggers, illness or infection with a fever was most common. Pharmacologic treatment was the primary management approach, with levetiracetam most frequently reported. Side effects were the most common reason for medication discontinuation, and only 69% of caregivers reported access to or use of an acute seizure rescue medication. CONCLUSIONS:Caregiver-reported data from the Linking Angelman and Dup15q Data for Expanded Research Database provide an updated characterization of seizures in AS. Gaps in trigger identification and availability or use of rescue medications highlight opportunities to improve standard-of-care implementation in AS.

Seizures are often induced by electrical stimulation (stim seizures) during intracranial EEG (iEEG) evaluation for epilepsy surgery, but their value for localizing seizure generating tissue remains unclear. We compared 441 low-frequency (1 Hz) stim and spontaneous seizures in a multi-center cohort of 105 patients using a novel, state-of-the-art validated automated seizure mapping algorithm. We found that stim seizures recruit a smaller, more spatially restricted network than spontaneous seizures that overlaps with their onset and propagation. Stim seizures with habitual semiology exhibited onset zones indistinguishable from spontaneous seizures. Both clinically habitual and non-habitual stim seizure onset zones were rapidly recruited during spontaneous seizures, suggesting that they arise from hyperexcitable, epileptogenic, tissue. Stim seizures preferentially originated from pathological mesial temporal structures, especially in adult-onset epilepsy. We propose that stimulation mapping has potential to supplant recording spontaneous seizures, and hypothesize that the method may identify portions of epileptic networks susceptible to seizure recurrence after focal interventions.

Minimally invasive procedures such as MRI-guided LiTT are increasingly being utilized in pediatric epilepsy patients; however, their clinical efficacy has been limited by challenges in precisely localizing epileptogenic tissues. A precise and accurate means to highlight epileptogenic tissues noninvasively will augment the utility of LiTT. Previous studies have suggested that an apparent diffusion coefficient (ADC) map may highlight microstructural abnormalities commonly seen in temporal lobe epilepsy and provide a prognosis for seizure freedom following LiTT. Twelve pediatric epilepsy patients who underwent unilateral amygdalohippocampal SEEG were reviewed. Based on preoperative ADC sequences of each patient, a machine-learning algorithm was employed to detect hyperintensive ADC clusters within the hippocampus and amygdala ipsilateral to SEEG-implanted hemisphere. In parallel, coordinates of SEEG-electrode contacts within 30mm of each ADC cluster where abnormal interictal epileptiform discharges (“active” contacts), and contacts with no discharges (“passive” contacts) were identified. Euclidian distances between centroid of ADC hyperintensive clusters and locations of SEEG electrode contacts for each patient were calculated and compared between active and passive contacts. Cluster-SEEG contact distance was relatively shorter with active contacts than passive contacts in the hippocampus (17.3mm vs. 21.7mm, p=0.02). After fitting a multivariate logistic regression model predicting whether a contact is active or passive from cluster-contact distance measures, ROC analysis yielded a significant predictive capacity for hippocampal clusters (AUC=0.95, p=0.0013) for mean cluster distance, and both hippocampal (AUC=0.72, p <0.0001) and amygdala clusters (AUC=0.72, p=0.012) for individual cluster distance. Our results suggest that ADC hyperintensive clusters may co-localize with epileptiform activity detected in SEEG contacts, especially in hippocampus. Furthermore, our findings highlight the potential utility of preoperative diffusion-weighted imaging in precisely capturing locations with epileptiform discharges inferred by SEEG recordings.

Rett syndrome is a rare neurodevelopmental disorder caused primarily by pathogenic variants in the MECP2 gene, leading to lifelong cognitive impairments. To understand the broad neural disruptions in Rett syndrome, it is essential to examine large-scale brain dynamics at the level of neural oscillations. Phase-amplitude coupling-a form of cross-frequency interaction that supports information integration across temporal and spatial scales-is a promising candidate measure for capturing such widespread neural dysfunction. Phase-amplitude coupling depends on the coordinated activity of specific neuronal subtypes, and while multiple subtypes are implicated in different aspects of the Rett syndrome phenotype, their role in shaping large-scale oscillatory dynamics in Rett syndrome is not well understood. To investigate this, we utilized a multi-level approach, combining EEG recordings with computational modeling to identify alterations in phase-amplitude coupling in Rett syndrome and probe their underlying cellular and circuit-level mechanisms. We recorded resting-state EEG from 38 individuals with Rett syndrome and 30 age- and sex-matched typically developing individuals. Phase-amplitude coupling was quantified: modulation index was obtained to determine coupling strength, and phase bias was assessed to examine the preferred phase of coupling. We characterized phase-amplitude coupling across all low and high frequency combinations and electrodes, as well as within canonical theta-gamma and alpha-gamma frequency pairs across four predefined cortical regions. Finally, we modeled a biophysically-constrained Layer 4 cortical network to propose a possible mechanism underlying changes to oscillatory dynamics. We found significantly stronger phase-amplitude coupling in Rett syndrome across widespread cortical regions and frequency pairs, with a pronounced increase in theta-gamma and alpha-gamma coupling in anterior, posterior, and whole-brain regions (P < 0.05). Individuals with Rett syndrome also exhibited a more positive alpha-gamma phase bias in anterior and whole-brain regions (P < 0.05). Biophysically constrained modelling demonstrated that reduced VIP-expressing interneuron activity alone could recapitulate the pattern of increased theta-gamma and alpha-gamma phase-amplitude coupling observed in Rett syndrome (P < 0.001). These findings identify alterations in awake-state phase-amplitude coupling in Rett syndrome and propose a mechanistic link to VIP+ interneuron dysfunction. Elevated phase-amplitude coupling may serve as a promising biomarker of cortical dysfunction and a translational bridge from neural circuitry to clinically observable EEG signatures. By implicating VIP+ interneurons, our results open new avenues for testing interventions in preclinical models to identify potential novel therapeutic targets for individuals with Rett syndrome.

BACKGROUND:Focal epilepsy arising from the eloquent cortex can be treated with palliative surgical interventions such as multiple subpial transection (MST) or responsive neurostimulation (RNS). These techniques can be performed to reduce the burden of disabling seizures while avoiding disability associated with resection of the eloquent brain. OBSERVATIONS:A 17-year-old girl with a history of complex, refractory multifocal epilepsy and previous right anterior temporal lobectomy and left temporal neocortical RNS presented with refractory status epilepticus. Scalp electroencephalography showed seizures that began prior to RNS detection, suggesting a focus outside of the left anterior temporal lobe. MRI showed new edema throughout the left insula. MST and concurrent insular RNS lead placement were performed. The patient was discharged 2 weeks later, and at the 6-month follow-up, she had a 100-fold reduction in clinical seizures and RNS detections. LESSONS:This technical report is the first description of 1) concurrent MST and RNS, and 2) placement of a paddle electrode for the RNS over the surface of the insula using a transsylvian approach. Surgery in this case provided both immediate and sustained reduction in disabling seizures over several months. https://thejns.org/doi/10.3171/CASE24445.

BACKGROUND:FOXG1 syndrome is rare neurodevelopmental disorder with microcephaly, brain malformations, epilepsy, and cognitive and motor disabilities as major features. Knowledge of the clinical features is primarily from case series and a foundation sponsored registry. We expand insight into epilepsy in FOXG1 syndrome by examining longitudinal data from 94 individuals from a multi-site natural history study and local cohorts. METHODS:Clinical information on severity, seizure type, and seizure features was collected from 68 individuals enrolled in the Rett Syndrome and Related Disorders Natural History Study and extracted via retrospective chart review from 15 individuals seen at the Children's Hospital of Philadelphia Rett Syndrome Center of Excellence and 11 individuals from Children's Hospital of Colorado. Genotype-phenotype and other correlations were assessed using non- and semi-parametric analyses. RESULTS:78.7 % of participants had seizures, beginning at a median age of 1.0 years. Individuals were followed for a median of 4.9 years after first seizure onset. Taken independently, over 70 % of seizures were partial or tonic-clonic, occurred less than weekly, and lasted less than 5 min. 1/3 of seizures resolved in a median time and age of 1.1 and 3.3 years. Age had a weak non-linear association with average seizure frequency, and, for those with seizures, smaller head circumference correlated with increased disease severity. CONCLUSIONS:We further characterize disease severity and epilepsy in FOXG1 syndrome and demonstrate that smaller head circumferences are associated with more severe disease and age is weakly non-linearly correlated with average seizure frequency. This information will improve clinical care and aid therapeutic development.

CDKL5 deficiency disorder is a rare and severe developmental and epileptic encephalopathy that has profound effects on communication. It is essential that communication be measured accurately for upcoming gene therapy trials. The Communication Inventory Disability-Observer Reported (CID-OR) was developed from a framework of communication derived from parent/caregiver interview data (n = 23), in consultation with disability and communication experts, and after reviewing concepts in existing measures. In this study, parents and caregivers (n = 21) took part in 1-hour semistructured think-aloud online interviews. A directed content analysis was conducted using both deductive and inductive coding. Findings suggest that CID-OR was comprehensive, comprehensible, and relevant. Multiple small adjustments were made to improve clarity and representativeness and reduce caregiver burden based on feedback in the data. This content validity study is an important element in the process of developing an effective measure of communication of people with CDKL5 deficiency disorder.

BACKGROUND: FOXG1 syndrome is a severe genetic neurodevelopmental disorder characterized by intellectual and developmental disabilities (IDD), postnatal microcephaly, epilepsy, and movement disorder. With the advent of molecular therapies, establishing the natural history of FOXG1 syndrome is critical to enable clinical trial readiness. However, traditional study designs are challenging to implement for rare disorders without significant burden to participants. METHODS: The study population included 101 children and adults with (likely) pathogenic variants in or involving FOXG1 (ages 0.4 - 34.8 years). Participant medical records underwent systematic annotation and harmonization of recorded clinical phenotypes, interventions, and outcomes through use of a patient-centric real-world data (RWD) platform. Retrospective medical record data were paired with prospective administration of validated measures of development and behavior, including the Vineland-3, the Aberrant Behavior Checklist, and the Children’s Sleep Habits Questionnaire. Descriptive and inferential statistics were employed to characterize longitudinal phenotypes and to explore genotype-phenotype correlations. RESULTS: Through systematic evaluation of 101 people with FOXG1 syndrome, we generated a robust dataset encompassing >40,000 annotated clinical terminology concepts that represent >770 cumulative patient data years. Core clinical phenotypes include IDD, gastrointestinal disorders, strabismus, epilepsy, movement disorders, and sleep problems. The FOXG1 syndrome behavioral phenotype is characterized by irritability, including aggressive behaviors, stereotypies, social withdrawal, and lethargy; in those with missense variants, features of autism spectrum disorders are also reported. Data derived from both medical records and validated measures confirm and expand upon previously described genotype-phenotype correlations, whereby truncating variants are associated with greater limitations across motor and communication domains, as well as increased frequency of core FOXG1 syndrome phenotypes. Further, individuals with truncating variants had higher scores on a composite measure of FOXG1 syndrome severity, which persists when modeled longitudinally. Employing the same composite measure, we demonstrate that FOXG1 syndrome is a static encephalopathy without evidence of neurodegeneration. CONCLUSIONS: By combining retrospective RWD with prospective survey administration in a large sample population, we establish the natural history of FOXG1 syndrome and highlight candidate clinical endpoints for use in clinical trials, including quantitative evaluations of communication and movement disorders.

Cortical stimulation is the process of delivering brief pulses of electrical current and visualizing the distributed pattern of evoked responses across the brain. Compared to high-frequency stimulation, which has long been used for seizure provocation and functional mapping, low-frequency stimulation (<1–2 Hz) is rarely incorporated into the epilepsy surgery evaluation. Increasingly, researchers have demonstrated that various cortico-cortical evoked potential (CCEP) features, including early and delayed responses, evoked high-frequency oscillations, and derived network metrics, may be useful biomarkers of tissue excitability and abnormal connectivity. Emerging evidence also highlights a potential role of CCEPs in guiding neuromodulatory therapies like responsive neurostimulation. In this review, we examine the past two decades of innovation in low-frequency stimulation as it pertains to pre-surgical evaluation. We begin with a basic overview of single-pulse electrical stimulation and CCEPs, including definitions, methodology, physiology, and traditional interpretation. We then explore the literature examining CCEPs as markers of cortical excitability, seizure onset, and network-level dysfunction. Finally, the relationship between stimulation-induced and spontaneous seizures is considered. By examining these questions, we identify both opportunities and pitfalls along the path towards integrating low-frequency stimulation into clinical practice.

CDKL5 deficiency disorder (CDD) is a rare developmental and epileptic encephalopathy. Greater understanding of the smallest meaningful improvements for individuals with CDD in clinical trials and practice is needed for a person-centred approach to treatment efficacy. This study explored how parent/caregivers of people with CDD understood meaningful improvements and described change for priority functional domains including communication, gross motor, fine motor, feeding. This study included an in-person workshop and a convergent mixed-methods online survey. Parent/caregivers (n = 19) attending the 6th Family Educational and Awareness Conference for CDD participated in discussion groups for the workshop component. The survey (n = 80) collected descriptive data and open-ended responses. Qualitative data were stratified by ability levels and analysed using a conventional content analysis. Definitions of meaningful improvement varied in terms of desired speed and magnitude of change and included health and skill stability. Parent/caregivers described meaningful increases in developmental skills that were specific to each domain and level of ability. Some concepts were common across ability levels within domains (e.g., increased independence across all gross motor levels) and others were consistent across domains (e.g., improved utensil use in fine motor and feeding domains). Meaningful improvement means different things to different people with some factors consistent regardless of ability level suggesting important underlying concepts for measurement requiring future investigation. These findings can contribute to the development of clinical treatments and trials that focus on factors that are important to people with CDD and their families.

There is increasing interest in the utility of electrophysiological measures such as resting EEG and evoked potential (EPs) to serve as biomarkers to facilitate therapeutic development for rare genetic neurodevelopmental disorders (NDDs). Research on this topic thus far has been encouraging, but has also revealed the necessity for unique methods when acquiring EEG and EPs in children with genetic NDDs. Details of these methods are typically beyond the scope of research publications, yet are crucial to the quality and ultimately, usability of the data. In the current manuscript, we detail the methods that we have developed for acquiring EEG and EPs as part of multi-site studies with participants with Rett syndrome, CDKL5 deficiency disorder, MECP2 duplication syndrome, and FOXG1 syndrome. By making our methods accessible, we hope to support other groups interested in acquiring EEG and/or EPs as part of clinical trials or research studies with individuals with genetic NDDs, including groups without prior experience with EEG/EP acquisition. The paper is presented as step-by-step procedures followed by a discussion of issues that may arise during acquisition and ways to troubleshoot these issues. We then discuss considerations for choosing EEG equipment and study paradigms and briefly, considerations for data analysis.

Rett syndrome (RTT) is a rare neurodevelopmental disorder typically caused by loss-of-function variants in the transcriptional regulator methyl-CpG binding protein-2 (MECP2) gene. These variants were historically believed to be incompatible with life in males; however, recent advances in genetic testing have revealed significant clinical heterogeneity. The current study aimed to improve our understanding of diagnostic experiences in males with confirmed pathogenic alteration of MECP2. An international sample of caregivers completed a survey of diagnostic experiences (N = 47) and phenomenological interviews (n = 32). Median [interquartile range; IQR] age of genetic diagnosis was 3 years [1.08, 6.75]. Multivariate analysis showed that for every year increase in year of birth, age of diagnosis (in years) decreased by 0.31. Qualitative findings demonstrate that medical biases and widespread misconceptions contribute to delays in accurate clinical diagnosis, which negatively impacts child health and family functioning. As genetic testing becomes more widely available, age of genetic diagnosis is decreasing, resulting in more providers and families with unexpected results and a notable lack of male-specific anticipatory guidance and clinical recommendations. Diagnostic providers must increase their awareness of males with confirmed pathogenic alterations of MECP2 and be prepared to deliver the diagnosis with empathy and accurate, up-to-date information on prognosis and treatment options.

Seizures are increasingly understood as emergent phenomena of complex, pathophysiologic networks. Interictal spikes are ubiquitous markers of paroxysmal synchronization in the epileptic brain and have been shown to co-activate between brain regions with millisecond-scale latencies, suggesting that they can spread through distributed networks of functionally inter-connected neuronal populations. In this study, we examined the relationship between interictal spike co-activation, seizure localization and resting-state EEG activity in children with medically refractory epilepsy. Twenty paediatric patients (mean age: 10.6 years) undergoing invasive EEG investigation with subdural electrodes were examined. Automated techniques were used to extract time-varying interictal spike co-activation networks from full-duration interictal recordings (mean: 108.6 h/patient). Networks were clustered into discrete node communities based on the conditional probability of spike co-activation. Patterns of regional and distributed interictal spike synchrony were investigated over time in relation to variables such as temporal proximity to nearest seizure and background oscillatory coherence. We demonstrate that the irritative neocortex comprises a network of semi-independent, highly cohesive communities with stereotyped local spike propagation patterns. Distributed coupling of spikes between communities was driven by outflow from the seizure onset zone and fluctuated over time in association with inter-regional coherence and temporal proximity to seizures. These results elucidate network dynamics facilitating pathologic hypersynchrony across the epileptic neocortex and further highlight the complex relationship between interictal epileptiform discharges and seizures.

ABSTRACT Objective We aim to assess the clinical features of Rett syndrome (RTT) at registration into the National Institutes of Health–sponsored natural history study (NHS) using the Clinical Severity Scale (CSS). Introduction The CSS was established in 2000 to assess characteristics of individuals with RTT and related disorders. We analyzed the CSS at enrollment into the NHS of all individuals with classic RTT. Methods The CSS of 1258 individuals was used to examine three historical items (age at regression, age at onset of hand stereotypies, and head growth) and 10 clinical features at initial enrollment. Results Among historical items, age at regression was most prominent after age 12 months with 8% regressing before this, hand stereotypies were most common after 18 months with 30% occurring before, and head growth was substantially lower overall. Hand use, ambulation, and communication skills were reduced in most individuals. Discussion and Conclusion These findings reflect core clinical criteria for classic RTT and mirror the top concerns registered independently by parents or caregivers. The CSS is an important analytic tool for the association of relative differences in clinical outcome with specific MECP2 variant groups and has been important in establishing entrance criteria in RTT clinical trials. The range of age‐specific CSS features will continue to inform the RTT natural natural history as well as provide stratification and selection in future clinical trials, especially those involving younger participants.