The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders.

Inherited glycosylphosphatidylinositol deficiency disorders (IGDs) are a group of rare multisystem disorders arising from pathogenic variants in glycosylphosphatidylinositol anchor pathway (GPI-AP) genes. Despite associating 24 of at least 31 GPI-AP genes with human neurogenetic disease, prior reports are limited to single genes without consideration of the GPI-AP as a whole and with limited natural history data. In this multinational retrospective observational study, we systematically analyse the molecular spectrum, phenotypic characteristics, and natural history of 83 individuals from 75 unique families with IGDs, including 70 newly reported individuals: the largest single cohort to date. Core clinical features were developmental delay or intellectual disability (DD/ID, 90%), seizures (83%), hypotonia (72%), and motor symptoms (64%). Prognostic and biologically significant neuroimaging features included cerebral atrophy (75%), cerebellar atrophy (60%), callosal anomalies (57%), and symmetric restricted diffusion of the central tegmental tracts (60%). Sixty-one individuals had multisystem involvement including gastrointestinal (66%), cardiac (19%), and renal (14%) anomalies. Though dysmorphic features were appreciated in 82%, no single dysmorphic feature had a prevalence >30%, indicating substantial phenotypic heterogeneity. Follow-up data were available for all individuals, 15 of whom were deceased at the time of writing. Median age at seizure onset was 6 months. Individuals with variants in synthesis stage genes of the GPI-AP exhibited a significantly shorter time to seizure onset than individuals with variants in transamidase and remodelling stage genes of the GPI-AP (P=0.046). Forty individuals had intractable epilepsy. The majority of individuals experienced delayed or absent speech (95%); motor delay with non-ambulance (64%); and severe-to-profound DD/ID (59%). Individuals with a developmental epileptic encephalopathy (51%) were at greater risk of intractable epilepsy (P=0.003), non-ambulance (P=0.035), ongoing enteral feeds (P<0.001), and cortical visual impairment (P=0.007). Serial neuroimaging showed progressive cerebral volume loss in 87.5% and progressive cerebellar atrophy in 70.8%, indicating a neurodegenerative process. Genetic analyses identified 93 unique variants (106 total), including 22 novel variants. Exploratory analyses of genotype-phenotype correlations using unsupervised hierarchical clustering identified novel genotypic predictors of clinical phenotype and long-term outcome with meaningful implications for management. In summary, we expand both the mild and severe phenotypic extremities of the IGDs; provide insights into their neurological basis; and, vitally, enable meaningful genetic counselling for affected individuals and their families.

Genotype-phenotype associations in 1018 individuals with SCN1A-related epilepsies.

OBJECTIVE: SCN1A variants are associated with epilepsy syndromes ranging from mild genetic epilepsy with febrile seizures plus (GEFS+) to severe Dravet syndrome (DS). Many variants are de novo, making early phenotype prediction difficult, and genotype-phenotype associations remain poorly understood. METHODS: We assessed data from a retrospective cohort of 1018 individuals with SCN1A-related epilepsies. We explored relationships between variant characteristics (position, in silico prediction scores: Combined Annotation Dependent Depletion (CADD), Rare Exome Variant Ensemble Learner (REVEL), SCN1A genetic score), seizure characteristics, and epilepsy phenotype. RESULTS: DS had earlier seizure onset than other GEFS+ phenotypes (5.3 vs. 12.0 months, p < .001). In silico variant scores were higher in DS versus GEFS+ (p < .001). Patients with missense variants in functionally important regions (conserved N-terminus, S4-S6) exhibited earlier seizure onset (6.0 vs. 7.0 months, p = .003) and were more likely to have DS (280/340); those with missense variants in nonconserved regions had later onset (10.0 vs. 7.0 months, p = .036) and were more likely to have GEFS+ (15/29, χ2 = 19.16, p < .001). A minority of protein-truncating variants were associated with GEFS+ (10/393) and more likely to be located in the proximal first and last exon coding regions than elsewhere in the gene (9.7% vs. 1.0%, p < .001). Carriers of the same missense variant exhibited less variability in age at seizure onset compared with carriers of different missense variants for both DS (1.9 vs. 2.9 months, p = .001) and GEFS+ (8.0 vs. 11.0 months, p = .043). Status epilepticus as presenting seizure type is a highly specific (95.2%) but nonsensitive (32.7%) feature of DS. SIGNIFICANCE: Understanding genotype-phenotype associations in SCN1A-related epilepsies is critical for early diagnosis and management. We demonstrate an earlier disease onset in patients with missense variants in important functional regions, the occurrence of GEFS+ truncating variants, and the value of in silico prediction scores. Status epilepticus as initial seizure type is a highly specific, but not sensitive, early feature of DS.

From diagnosis to treatment in genetic epilepsies: Implementation of precision medicine in real-world clinical practice.

The implementation of whole exome sequencing (WES) has had a major impact on the diagnostic yield of genetic testing in individuals with epilepsy. The identification of a genetic etiology paves the way to precision medicine: an individualized treatment approach, based on the disease pathophysiology. The aim of this retrospective cohort study was to: (1) determine the diagnostic yield of WES in a heterogeneous cohort of individuals with epilepsy referred for genetic testing in a real-world clinical setting, (2) investigate the influence of epilepsy characteristics on the diagnostic yield, (3) determine the theoretical yield of treatment changes based on genetic diagnosis and (4) explore the barriers to implementation of precision medicine. WES was performed in 247 individuals with epilepsy, aged between 7 months and 68 years. In 34/247 (14 %) a (likely) pathogenic variant was identified. In 7/34 (21 %) of these individuals the variant was found using a HPO-based filtering. Diagnostic yield was highest for individuals with an early onset of epilepsy (39 %) or in those with a developmental and epileptic encephalopathy (34 %). Precision medicine was a theoretical possibility in 20/34 (59 %) of the individuals with a (likely) pathogenic variant but implemented in only 11/34 (32 %). The major barrier to implementation of precision treatment was the limited availability or reimbursement of a given drug. These results confirm the potential impact of genetic analysis on treatment choices, but also highlight the hurdles to the implementation of precision medicine. To optimize precision medicine in real-world practice, additional endeavors are needed: unifying definitions of precision medicine, establishment of publicly accessible databases that include data on the functional effect of gene variants, increasing availability and reimbursement of precision therapeutics, and broadening access to innovative clinical trials.

Functional mobility in children and young adults with Dravet syndrome.

AIM: This cohort study aimed to describe functional mobility in Dravet syndrome, a developmental and epileptic encephalopathy. METHOD: Functional mobility was assessed in individuals (aged 3-25 years), diagnosed with Dravet syndrome, using the Functional Mobility Scale (FMS), Mobility Questionnaire 28 (MobQues28), and estimated walking distance. Secondary outcome variables were Gait Profile Score (GPS), walking velocity, age at independent walking, intellectual disability, seizure frequency, genetic variant type, and body mass index (BMI). RESULTS: Forty participants aged 3 years to 24 years 2 months (mean = 12 years 2 months) had a median MobQues28 of 79%, median scores of 5, 5, and 4 for the FMS 5 m, 50 m, and 500 m and a median estimated walking distance of 1 km to 3 km. Most difficulties were seen in walking up and down the stairs, walking over obstacles, kicking a ball, and running. MobQues28 scores showed a significant decrease (-6.6%, p = 0.016) in the age category of young adults (≥18 years). After correcting for age, MobQues28 was correlated to age at independent walking (-0.485, p = 0.002), GPS (-0.460, p = 0.003), and walking velocity (0.334, p = 0.038). Analysis of variance showed a significant effect of intellectual disability and BMI on MobQues28 (p = 0.029, p = 0.049). No effect of seizure frequency or genetic variant was found (p = 0.579, p = 0.337). INTERPRETATION: Functional mobility limitations were observed mainly in dual tasks and activities requiring stability, with limitations increasing from the age of 18 years. Age at independent walking, gait impairments, intellectual disability, and BMI can impact functional mobility in Dravet syndrome. WHAT THIS PAPER ADDS: Most limitations were seen in dual task activities and activities that required more stability. Deterioration in functional mobility occurred in young adults. The more gait impairments, the more functional mobility limitations. Age at independent walking, intellectual disability, and body mass index can impact functional mobility.

Therapeutic drug monitoring of fenfluramine in clinical practice: Pharmacokinetic variability and impact of concomitant antiseizure medications.

OBJECTIVE: This study was undertaken to determine the plasma concentration and pharmacokinetic variability of fenfluramine (FFA) and its main active metabolite norfenfluramine (norFFA) in relation to the prevalence of adverse effects in patients with refractory epilepsy treated with FFA. In addition, the interaction with concomitant antiseizure medications including stiripentol (STP) is studied. METHODS: Patients were recruited at our center from two open-label sources, an investigator-initiated observational study and an international multicenter extension study. Venous blood samples were collected between June 2015 and December 2020. Plasma FFA and norFFA concentrations were determined by liquid chromatography tandem spectrometric analysis. Clinical data were collected retrospectively. Intrapatient coefficient of variation was calculated for all patients with at least three samples. Interpatient variability was calculated based on the concentration to weight-adjusted dose ratio (C/D) of all patients. RESULTS: We collected 321 samples from 61 patients (49 with Dravet syndrome, seven with Lennox-Gastaut syndrome, and five with a developmental and epileptic encephalopathy). With a mean daily dose of .33 mg/kg/day (SD = ±.16), the median FFA plasma concentration was 41.4 µg/L (range = 5.1-712.5) and median norFFA concentration 28.1 µg/L (range = 2.6-149.6). The FFA plasma concentration was linearly related to the daily dose (p < .001) and norFFA levels (p < .001). The C/D of FFA increased with age (p < .001). Median FFA C/D was 428% higher (p < .001), norFFA C/D 83% lower (p < .001), and norFFA/FFA 23% lower (p < .001) in patients treated with STP comedication. Higher FFA concentration was associated with fatigue (p = .001) and somnolence (p < .001), but not anorexia (p = .0619) or reduction in seizure frequency (p = .772). Gender and other ASMs were not associated with significant variations in (nor)FFA C/D ratio. SIGNIFICANCE: Most FFA levels are in the lower range (<50 µg/L), although a high interpatient and intrapatient variability is present. In combination with STP, the dose of FFA should be reduced.

Development and Validation of a Prediction Model for Early Diagnosis of SCN1A-Related Epilepsies.

BACKGROUND AND OBJECTIVES: Pathogenic variants in the neuronal sodium channel α1 subunit gene (SCN1A) are the most frequent monogenic cause of epilepsy. Phenotypes comprise a wide clinical spectrum, including severe childhood epilepsy; Dravet syndrome, characterized by drug-resistant seizures, intellectual disability, and high mortality; and the milder genetic epilepsy with febrile seizures plus (GEFS+), characterized by normal cognition. Early recognition of a child's risk for developing Dravet syndrome vs GEFS+ is key for implementing disease-modifying therapies when available before cognitive impairment emerges. Our objective was to develop and validate a prediction model using clinical and genetic biomarkers for early diagnosis of SCN1A-related epilepsies. METHODS: We performed a retrospective multicenter cohort study comprising data from patients with SCN1A-positive Dravet syndrome and patients with GEFS+ consecutively referred for genetic testing (March 2001-June 2020) including age at seizure onset and a newly developed SCN1A genetic score. A training cohort was used to develop multiple prediction models that were validated using 2 independent blinded cohorts. Primary outcome was the discriminative accuracy of the model predicting Dravet syndrome vs other GEFS+ phenotypes. RESULTS: A total of 1,018 participants were included. The frequency of Dravet syndrome was 616/743 (83%) in the training cohort, 147/203 (72%) in validation cohort 1, and 60/72 (83%) in validation cohort 2. A high SCN1A genetic score (133.4 [SD 78.5] vs 52.0 [SD 57.5]; p < 0.001) and young age at onset (6.0 [SD 3.0] vs 14.8 [SD 11.8] months; p < 0.001) were each associated with Dravet syndrome vs GEFS+. A combined SCN1A genetic score and seizure onset model separated Dravet syndrome from GEFS+ more effectively (area under the curve [AUC] 0.89 [95% CI 0.86-0.92]) and outperformed all other models (AUC 0.79-0.85; p < 0.001). Model performance was replicated in both validation cohorts 1 (AUC 0.94 [95% CI 0.91-0.97]) and 2 (AUC 0.92 [95% CI 0.82-1.00]). DISCUSSION: The prediction model allows objective estimation at disease onset whether a child will develop Dravet syndrome vs GEFS+, assisting clinicians with prognostic counseling and decisions on early institution of precision therapies (http://scn1a-prediction-model.broadinstitute.org/). CLASSIFICATION OF EVIDENCE: This study provides Class II evidence that a combined SCN1A genetic score and seizure onset model distinguishes Dravet syndrome from other GEFS+ phenotypes.

A critical evaluation of fenfluramine hydrochloride for the treatment of Dravet syndrome.

INTRODUCTION: Dravet Syndrome (DS) is a severe developmental and epileptic encephalopathy. Fenfluramine recently demonstrated to be a highly efficacious and safe treatment option for DS patients. Fenfluramine has been recently approved by the FDA and EMA and is marketed as Fintepla®. AREAS COVERED: DS and the need for additional anticonvulsive treatment options is discussed. The results of three placebo-controlled phase III studies (1 with and 2 without stiripentol) and 2 open label (extension) studies are reviewed. All studies demonstrate a consistent and impressive seizure reduction, confirming the results of two smaller investigator-initiated trials. The mechanism of action of fenfluramine is discussed. Finally, the place of fenfluramine in the future treatment of DS is outlined. EXPERT OPINION: Fenfluramine has a potent anticonvulsive effect in DS. Although not yet fully elucidated, the anticonvulsive mechanism of fenfluramine seems to be mainly serotonergic. Fenfluramine is generally well tolerated. A dose reduction is necessary in combination with stiripentol. Considering new competitors, efficacy seems lower for cannabidiol and is comparable with stiripentol. Preclinical studies indicate a disease specific action and possible disease modification in DS. The latter would support the use of fenfluramine above its anticonvulsive effect and needs to be further elaborated.

Impact of fenfluramine on the expected SUDEP mortality rates in patients with Dravet syndrome.

PURPOSE: To assess the impact of fenfluramine (FFA) on the expected mortality incidence, including sudden unexpected death in epilepsy (SUDEP), in persons with Dravet syndrome (DS). METHODS: In this pooled analysis, total time of exposure for persons with DS who were treated with FFA in phase 3 clinical trials, in United States and European Early Access Programs, and in two long-term open-label observational studies in Belgium was calculated. Literature was searched for reports of SUDEP mortality in DS, which were utilized as a comparison. Mortality rates were expressed per 1000 person-years. RESULTS: A total of 732 persons with DS were treated with FFA, representing a total of 1185.3 person-years of exposure. Three deaths occurred, all in the phase 3 program: one during placebo treatment (probable SUDEP) and two during treatment with FFA (one probable SUDEP and one definite SUDEP). The all-cause and SUDEP mortality rates during treatment with FFA was 1.7 per 1000 person-years (95% CI, 0.4 to 6.7), a value lower than the all-cause estimate of 15.8 per 1000 person-years (95% CI, 9.9 to 25.4) and SUDEP estimate of 9.3 (95% CI, 5.0 to 17.3) reported by Cooper et al. (Epilepsy Res 2016;128:43-7) for persons with DS receiving standard-of-care. CONCLUSION: All-cause and SUDEP mortality rates in DS patients treated with FFA were substantially lower than in literature reports. Further studies are warranted to confirm that FFA reduces SUDEP risk in DS patients and to better understand the potential mechanism(s) by which FFA lowers SUDEP risk. CLINICAL TRIAL REGISTRATION: NCT02926898, NCT02682927, NCT02826863, NCT02823145, NCT03780127.

Strength measurements in patients with Dravet Syndrome.

BACKGROUND: Dravet Syndrome (DS) is a developmental and epileptic encephalopathy, characterized by drug resistant infantile onset seizures and cognitive and motor impairment. Walking problems progressively occur and crouch gait is frequently observed. Muscle weakness is hypothesized as contributing impairment. Yet, so far, no studies have performed strength measurements in patients with DS, most likely due to cognitive impairment. AIMS: To determine the feasibility and validity of strength measurements in the framework of gait analysis and to outline strength problems in patients with DS. METHODS: Manual muscle testing, dynamometry (hand grip strength and handheld dynamometry) and functional tests (underarm throwing, standing long jump, sit-to-stand, stair climbing) were performed in 46 patients with DS. Results were compared to age-related reference values from literature. RESULTS: Forty one percent (19/46) of the patients (aged 5.2-24.8 years, median: 15.8 years) accomplished all measurements and scored generally below the fifth percentile of norm values. The remaining 59% (27/46) was not able to complete all strength assessment due to cognitive, behavioural and motor difficulties. Handheld dynamometry seemed most sensitive and specific to detect isolated muscle strength. Validity of the functional tests was controversial, as motor proficiency, balance and coordination may interfere. CONCLUSION: Although measuring strength in patients with DS was challenging in the context of gait analysis, decreased muscle strength was observed in patients that could perform strength measurements. Handheld dynamometry is preferred over functional tests for future investigations of muscle strength and its interference with gait are required for better understanding of walking problems.

KCNT1-related epilepsies and epileptic encephalopathies: phenotypic and mutational spectrum.

Variants in KCNT1, encoding a sodium-gated potassium channel (subfamily T member 1), have been associated with a spectrum of epilepsies and neurodevelopmental disorders. These range from familial autosomal dominant or sporadic sleep-related hypermotor epilepsy to epilepsy of infancy with migrating focal seizures (EIMFS) and include developmental and epileptic encephalopathies. This study aims to provide a comprehensive overview of the phenotypic and genotypic spectrum of KCNT1 mutation-related epileptic disorders in 248 individuals, including 66 previously unpublished and 182 published cases, the largest cohort reported so far. Four phenotypic groups emerged from our analysis: (i) EIMFS (152 individuals, 33 previously unpublished); (ii) developmental and epileptic encephalopathies other than EIMFS (non-EIMFS developmental and epileptic encephalopathies) (37 individuals, 17 unpublished); (iii) autosomal dominant or sporadic sleep-related hypermotor epilepsy (53 patients, 14 unpublished); and (iv) other phenotypes (six individuals, two unpublished). In our cohort of 66 new cases, the most common phenotypic features were: (i) in EIMFS, heterogeneity of seizure types, including epileptic spasms, epilepsy improvement over time, no epilepsy-related deaths; (ii) in non-EIMFS developmental and epileptic encephalopathies, possible onset with West syndrome, occurrence of atypical absences, possible evolution to developmental and epileptic encephalopathies with sleep-related hypermotor epilepsy features; one case of sudden unexplained death in epilepsy; (iii) in autosomal dominant or sporadic sleep-related hypermotor epilepsy, we observed a high prevalence of drug-resistance, although seizure frequency improved with age in some individuals, appearance of cognitive regression after seizure onset in all patients, no reported severe psychiatric disorders, although behavioural/psychiatric comorbidities were reported in ∼50% of the patients, sudden unexplained death in epilepsy in one individual; and (iv) other phenotypes in individuals with mutation of KCNT1 included temporal lobe epilepsy, and epilepsy with tonic-clonic seizures and cognitive regression. Genotypic analysis of the whole cohort of 248 individuals showed only missense mutations and one inframe deletion in KCNT1. Although the KCNT1 mutations in affected individuals were seen to be distributed among the different domains of the KCNT1 protein, genotype-phenotype considerations showed many of the autosomal dominant or sporadic sleep-related hypermotor epilepsy-associated mutations to be clustered around the RCK2 domain in the C terminus, distal to the NADP domain. Mutations associated with EIMFS/non-EIMFS developmental and epileptic encephalopathies did not show a particular pattern of distribution in the KCNT1 protein. Recurrent KCNT1 mutations were seen to be associated with both severe and less severe phenotypes. Our study further defines and broadens the phenotypic and genotypic spectrums of KCNT1-related epileptic conditions and emphasizes the increasingly important role of this gene in the pathogenesis of early onset developmental and epileptic encephalopathies as well as of focal epilepsies, namely autosomal dominant or sporadic sleep-related hypermotor epilepsy.

The mechanics behind gait problems in patients with Dravet Syndrome.

BACKGROUND: Dravet Syndrome (DS) is a developmental and epileptic encephalopathy starting in infancy and characterised by treatment resistant epilepsy with cognitive impairment and progressive motor dysfunction. Walking becomes markedly impaired with age, but the mechanical nature of gait problems remains unclear. RESEARCH QUESTION: What are the kinetic strategies characterised in gait of patients with DS? METHODS: This case-control study compared 41 patients with DS aged 5.2-26.1 years (19 female, 22 male) to 41 typically developing (TD) peers. Three dimensional gait analysis (VICON) was performed to obtain spatiotemporal parameters, kinematics and kinetics during barefoot, level walking at self-selected walking velocity. The sagittal plane support moment was analysed using Statistical Parametric Mapping (SPM). Three DS subgroups were identified based on differences in kinetic strategies characterised by the net internal knee joint moments and trunk lean. Kinematic and kinetic time profiles of the subgroups were compared to the TD group (SPM t-test). Clinical characteristics from physical examination and parental anamnesis were compared between DS (sub)groups using non-parametric tests (Kruskal-Wallis, Wilcoxon rank-sum, Fisher's exact). RESULTS: Support moments in stance were significantly increased in the DS group compared to TD and strongly related to minimum knee flexion in midstance. Persistent internal knee extension moments during stance were detected in a subgroup of 27 % of the patients. A second subgroup of 34 % showed forward trunk lean and attained internal knee flexion moments. The remaining 39 % had neutral or backward trunk lean with internal knee flexion moments. Subgroups differed significantly in age and functional mobility. SIGNIFICANCE: Inefficient kinetic patterns suggested that increased muscle effort was needed to control lower limb stability. Three distinct kinetic strategies that underly kinematic deviations were identified. Clinical evaluation of gait should pay attention to knee angles, trunk lean and support moments.

Independent walking and cognitive development in preschool children with Dravet syndrome.

AIM: To investigate the relation between cognitive and motor development in preschool aged children with Dravet syndrome, in particular between the age of independent walking and cognitive development. METHOD: Results of cognitive and motor developmental assessments and the age of independent walking were retrieved retrospectively from the medical records of 33 children (17 males, 16 females; mean age at last evaluation 33.2mo, SD 8.2mo, range 9-48mo) diagnosed with Dravet syndrome. Cognitive and motor developmental age, derived from the Bayley Scales of Infant Development or through standardized neurodevelopmental assessment, were converted into cognitive and motor developmental quotients. Multiple test scores per child were included. RESULTS: A strong positive relation was found between cognitive and motor developmental quotient (Pearson r=0.854; p<0.001) in 20 children (slope=0.75; 95% CI: 0.54-0.95). A later age of independent walking was associated with a lower cognitive developmental quotient (28 children; p<0.001; slope=-1.01; 95% CI: -1.53 to -0.49). A higher cognitive developmental quotient was seen in children with an age at testing younger than 24 months. The cognitive developmental quotient of children with a delay in independent walking (>17.6mo) was significantly lower than those without a delay (p=0.006). INTERPRETATION: A strong relation exists between cognitive and motor development. Furthermore, the age of independent walking might be an important indicator of the development of children with Dravet syndrome. WHAT THIS PAPER ADDS: Cognitive and motor development are strongly related in children with Dravet syndrome. Later age of independent walking is associated with worse cognitive development in children with Dravet syndrome.

Gait abnormalities in people with Dravet syndrome: A cross-sectional multi-center study.

OBJECTIVE: To quantify gait abnormalities in people with Dravet syndrome (DS). METHODS: Individuals with a confirmed diagnosis of DS were enrolled, and stratified according to knee flexion at initial contact (IC) and range of motion (ROM) during stance (atypical crouch: knee flexion >20° at IC and knee ROM >15° during stance; straight: knee flexion <20° at IC). A 1D ANOVA (α = 0.05) was used to test statistical differences among the joint kinematics and spatio-temporal parameters of the cohort and an age-matched control group. Clinical (neurological and orthopaedic evaluation) and anamnestic data (seizure type, drugs, genetic mutation) were collected; distribution between the two gait phenotypes was assessed with the Fisher exact test and, for mutation, with the chi-squared test (p < 0.05). Linear regression between maximum knee flexion and normalised walking speed was calculated. RESULTS: Seventy-one subjects were enrolled and evaluated with instrumented gait analysis. Fifty-two were included in final analysis (mean age 13.8 ± 7.3; M 26). Two gait patterns were detected: an atypical crouch gait (34.6%) with increased ankle, knee and hip flexion during stance, and reduced walking speed and stride length not associated with muscle-tendon retractions; and a pattern resembling those of healthy age-matched controls, but still showing reduced walking speed and stride length. No differences in clinical or anamnestic data emerged between the two groups. SIGNIFICANCE: Objectively quantified gait in DS shows two gait patterns with no clear-cut relation to clinical data. Kinematics abnormalities may be related to stabilization issues. These findings may guide rehabilitative and preventive measures.

Heterogeneous clinical and functional features of GRIN2D-related developmental and epileptic encephalopathy.

N-methyl d-aspartate receptors are ligand-gated ionotropic receptors mediating a slow, calcium-permeable component of excitatory synaptic transmission in the CNS. Variants in genes encoding NMDAR subunits have been associated with a spectrum of neurodevelopmental disorders. Here we report six novel GRIN2D variants and one previously-described disease-associated GRIN2D variant in two patients with developmental and epileptic encephalopathy. GRIN2D encodes for the GluN2D subunit protein; the GluN2D amino acids affected by the variants in this report are located in the pre-M1 helix, transmembrane domain M3, and the intracellular carboxyl terminal domain. Functional analysis in vitro reveals that all six variants decreased receptor surface expression, which may underline some shared clinical symptoms. In addition the GluN2D(Leu670Phe), (Ala675Thr) and (Ala678Asp) substitutions confer significantly enhanced agonist potency, and/or increased channel open probability, while the GluN2D(Ser573Phe), (Ser1271Phe) and (Arg1313Trp) substitutions result in a mild increase of agonist potency, reduced sensitivity to endogenous protons, and decreased channel open probability. The GluN2D(Ser573Phe), (Ala675Thr), and (Ala678Asp) substitutions significantly decrease current amplitude, consistent with reduced surface expression. The GluN2D(Leu670Phe) variant slows current response deactivation time course and increased charge transfer. GluN2D(Ala678Asp) transfection significantly decreased cell viability of rat cultured cortical neurons. In addition, we evaluated a set of FDA-approved NMDAR channel blockers to rescue functional changes of mutant receptors. This work suggests the complexity of the pathological mechanisms of GRIN2D-mediated developmental and epileptic encephalopathy, as well as the potential benefit of precision medicine.

Treatment Responsiveness in KCNT1-Related Epilepsy.

Pathogenic variants in KCNT1 represent an important cause of treatment-resistant epilepsy, for which an effective therapy has been elusive. Reports about the effectiveness of quinidine, a candidate precision therapy, have been mixed. We sought to evaluate the treatment responsiveness of patients with KCNT1-related epilepsy. We performed an observational study of 43 patients using a collaborative KCNT1 patient registry. We assessed treatment efficacy based upon clinical seizure reduction, side effects of quinidine therapy, and variant-specific responsiveness to treatment. Quinidine treatment resulted in a > 50% seizure reduction in 20% of patients, with rare patients achieving transient seizure freedom. Multiple other therapies demonstrated some success in reducing seizure frequency, including the ketogenic diet and vigabatrin, the latter particularly in patients with epileptic spasms. Patients with the best quinidine response had variants that clustered distal to the NADP domain within the RCK2 domain of the protein. Half of patients did not receive a quinidine trial. In those who did, nearly half did not achieve therapeutic blood levels. More favorable response to quinidine in patients with KCNT1 variants distal to the NADP domain within the RCK2 domain may suggest a variant-specific response.

Gait deviations in patients with dravet syndrome: A systematic review.

BACKGROUND: Dravet Syndrome is a rare developmental and epileptic encephalopathy characterised by epileptic seizures, cognitive impairment and motor disorders. Gait is markedly impaired and could benefit from targeted intervention to improve quality of life for patient and caregivers. OBJECTIVE: To establish the state of the art regarding gait deviations in patients with Dravet Syndrome. METHODS: A systematic search was performed in Pubmed, Web of Science, Science Direct and Embase. Studies that assessed gait deviations in patients diagnosed with Dravet Syndrome using clinical observation, video gait analysis or three dimensional (3D) gait analysis and reported gait characteristics, spatiotemporal or kinematic outcomes were included. Screening, quality assessment and data extraction were performed by independent reviewers. RESULTS: Out of a total of 478 citations, nine articles were included. The total study population had an age range from 2.5 to 47 years. Three studies used clinical observation, three studies video analysis and three studies 3D gait analysis. Crouch gait was observed in about half of the population next to a variety of other gait deviations such as parkinsonian and cerebellar gait. Other findings included abnormalities in spatiotemporal parameters and kinematics, passive knee extension deficits, skeletal malalignment and neurological signs. CONCLUSIONS: A variety of gait characteristics was observed with crouch gait being the most reported gait pattern. Inconsistency in methods and findings from clinical and instrumented evaluation impede thorough understanding of the causal mechanism and evolution behind these deviations. PROSPERO REGISTRATION NUMBER: CRD42017070370.

Diagnostic implications of genetic copy number variation in epilepsy plus.

OBJECTIVE: Copy number variations (CNVs) represent a significant genetic risk for several neurodevelopmental disorders including epilepsy. As knowledge increases, reanalysis of existing data is essential. Reliable estimates of the contribution of CNVs to epilepsies from sizeable populations are not available. METHODS: We assembled a cohort of 1255 patients with preexisting array comparative genomic hybridization or single nucleotide polymorphism array based CNV data. All patients had "epilepsy plus," defined as epilepsy with comorbid features, including intellectual disability, psychiatric symptoms, and other neurological and nonneurological features. CNV classification was conducted using a systematic filtering workflow adapted to epilepsy. RESULTS: Of 1097 patients remaining after genetic data quality control, 120 individuals (10.9%) carried at least one autosomal CNV classified as pathogenic; 19 individuals (1.7%) carried at least one autosomal CNV classified as possibly pathogenic. Eleven patients (1%) carried more than one (possibly) pathogenic CNV. We identified CNVs covering recently reported (HNRNPU) or emerging (RORB) epilepsy genes, and further delineated the phenotype associated with mutations of these genes. Additional novel epilepsy candidate genes emerge from our study. Comparing phenotypic features of pathogenic CNV carriers to those of noncarriers of pathogenic CNVs, we show that patients with nonneurological comorbidities, especially dysmorphism, were more likely to carry pathogenic CNVs (odds ratio = 4.09, confidence interval = 2.51-6.68; P = 2.34 × 10-9 ). Meta-analysis including data from published control groups showed that the presence or absence of epilepsy did not affect the detected frequency of CNVs. SIGNIFICANCE: The use of a specifically adapted workflow enabled identification of pathogenic autosomal CNVs in 10.9% of patients with epilepsy plus, which rose to 12.7% when we also considered possibly pathogenic CNVs. Our data indicate that epilepsy with comorbid features should be considered an indication for patients to be selected for a diagnostic algorithm including CNV detection. Collaborative large-scale CNV reanalysis leads to novel declaration of pathogenicity in unexplained cases and can promote discovery of promising candidate epilepsy genes.

Motor development in children with Dravet syndrome.

AIM: The aim of this study is to describe the course of motor development in children with Dravet syndrome. METHOD: Forty-three participants (21 males, 22 females; mean age at last assessment 53.89mo±42.50mo) met the inclusion criteria of having a confirmed diagnosis of Dravet syndrome and presence of data on motor development. All data between 1985 and 2018 were derived retrospectively from their medical records. Gross motor milestones and motor age equivalents were used to describe motor development. Standardized neurodevelopmental assessment and the Bayley Scales of Infant Development defined the overall motor development. Peabody Developmental Motor Scales, Bruininks-Oseretsky Test of Motor Proficiency, and the Beery-Buktenica Developmental Test of Visual-Motor Integration were used to describe development in specific motor domains. RESULTS: Children with Dravet syndrome showed a delay in both sitting (seven out of 14) and walking independently (11 out of 25). Overall motor age equivalents revealed a delay in 29 out of 38 assessments (age 9-115mo). All assessments of children older than 2 years (16 out of 16) showed a delay. Gross motor delay was present in seven out of seven and fine motor delay in 10 out of 13 assessments (age 19-167mo). INTERPRETATION: Motor development is delayed in the majority of children with Dravet syndrome older than 2 years and increases with age. WHAT THIS PAPER ADDS: A delay in motor development is present in most children with Dravet syndrome older than 2 years. Large diversity in early gross motor milestones confirms heterogeneity in Dravet syndrome.

Desarrollo motor en niños con el síndrome de Dravet OBJETIVO: El objetivo de este estudio es describir el curso del desarrollo motor en los niños con síndrome de Dravet. METODOLOGÍA: Cuarenta y tres participantes (21 niños, 22 niñas; con edad promedio en la última evaluación de 53,89 meses ± 42,50 meses) cumplieron los criterios de inclusión: tener un diagnóstico confirmado de síndrome de Dravet y presentar datos de desarrollo motor. Todos los datos recogidos entre 1,985 y 2,018 fueron extraídos retrospectivamente de las historias clínicas. Los hitos de motricidad gruesa y las equivalencias de edad motora se utilizaron para describir el desarrollo motor. Evaluaciones del neurodesarrollo estandarizadas y la escala de desarrollo infantil Bayley definieron el desarrollo motor global. La escala de desarrollo motor Peabody, el test de competencia motora Bruininks-Oseretsky y el test de desarrollo de la integración visomotora Beery-Buktenica se utilizaron para describir el desarrollo en los dominios motores específicos. RESULTADOS: Los niños con el síndrome de Dravet mostraron un retraso tanto en sentarse (7 de 14) como en caminar de manera independiente (11 de 25). En conjunto, las edades motoras equivalentes revelaron un retraso en 29 de las 38 evaluaciones (edad de 9-115 meses). Todas las evaluaciones de niños mayores de 2 años (16 de 16) mostraron un retraso. El retraso de la motricidad gruesa estuvo presente en 7 de 7 evaluaciones y el retraso de la motricidad fina en 10 de 13 evaluaciones (edad 19-167 meses). INTERPRETACIÓN: El desarrollo motor está retrasado en la mayoría de los niños con síndrome de Dravet mayores de dos años y aumenta con la edad.

Desenvolvimento motor em crianças com síndrome de Dravet OBJETIVO: O objetivo deste estudo é descrever o curso do desenvolvimento motor em crianças com síndrome de Dravet. MÉTODO: Quarenta e três participantes (21 do sexo masculino, 22 do sexo feminino; média de idade na última avaliação 53,89m ± 42,50m) atenderam aos critérios de inclusão de ter um diagnóstico confirmado de síndrome de Dravet e a presença de dados sobre o desenvolvimento motor. Todos os dados entre 1985 e 2018 foram derivados retrospectivamente de seus registros médicos. Marcos motores globais e idade motora equivalente foram usados para descrever o desenvolvimento motor. Avaliação padronizada do neurodesenvolvimento e a Escala Bayley de Desenvolvimento Infantil definiram o desenvolvimento global. A Escala Peabody de Desenvolvimento Motor, o Teste de Proficiência Motora de Bruininks-Oseretsky, e o Teste Desenvolvimental de Beery-Buktenica para Integração Visuo-motora foram usados para descrever o desenvolvimento em domínios motores específicos. RESULTADOS: Crianças com síndrome de Dravet mostraram atraso no sentar (sete em 14) e no andar independente (11 em 25). A idade motora global equivalente revelou atraso em 29 de 38 avaliações (idade 9-115m). Todas as avaliações de crianças com mais de 2 anos (16 de 16) mostraram atraso. O atraso motor global estava presente em sete de sete, e motor fino em 10 de 13 avaliações (idade 19-167m). INTERPRETAÇÃO: O desenvolvimento motor é atrasado na maioria das crianças com síndrome de Dravet maiores do que 2 anos, e aumenta com a idade.