Genotype-phenotype correlation in CLCN4-related developmental and epileptic encephalopathy

CLCN4-related disorder is a rare X-linked neurodevelopmental condition with a pathogenic mechanism yet to be elucidated. CLCN4 encodes the vesicular 2Cl-/H+ exchanger ClC-4, and CLCN4 pathogenic variants frequently result in altered ClC-4 transport activity. The precise cellular and molecular function of ClC-4 remains unknown; however, together with ClC-3, ClC-4 is thought to have a role in the ion homeostasis of endosomes and intracellular trafficking. We reviewed our research database for patients with CLCN4 variants and epilepsy, and performed thorough phenotyping. We examined the functional properties of the variants in mammalian cells using patch-clamp electrophysiology, protein biochemistry, and confocal fluorescence microscopy. Three male patients with developmental and epileptic encephalopathy were identified, with differing phenotypes. Patients #1 and #2 had normal growth parameters and normal-appearing brains on MRI, while patient #3 had microcephaly, microsomia, complete agenesis of the corpus callosum and cerebellar and brainstem hypoplasia. The p.(Gly342Arg) variant of patient #1 significantly impaired ClC-4's heterodimerization capability with ClC-3 and suppressed anion currents. The p.(Ile549Leu) variant of patient #2 and p.(Asp89Asn) variant of patient #3 both shift the voltage dependency of transport activation by 20 mV to more hyperpolarizing potentials, relative to the wild-type, with p.(Asp89Asn) favouring higher transport activity. We concluded that p.(Gly342Arg) carried by patient #1 and the p.(Ile549Leu) expressed by patient #2 impair ClC-4 transport function, while the p.(Asp89Asn) variant results in a gain-of-transport function; all three variants result in epilepsy and global developmental impairment, but with differences in epilepsy presentation, growth parameters, and presence or absence of brain malformations.

NEXMIF variants are associated with epilepsy with or without intellectual disability

OBJECTIVES

Variants in NEXMIF had been reported associated with intellectual disability (ID) without epilepsy or developmental epileptic encephalopathy (DEE). It is unkown whether NEXMIF variants are associated with epilepsy without ID. This study aims to explore the phenotypic spectrum of NEXMIF and the genotype-phenotype correlations.

MATERIALS AND METHODS

Trio-based whole-exome sequencing was performed in patients with epilepsy. Previously reported NEXMIF variants were systematically reviewed to analyze the genotype-phenotype correlations.

RESULTS

Six variants were identified in seven unrelated cases with epilepsy, including two de novo null variants and four hemizygous missense variants. The two de novo variants were absent in all populations of gnomAD and four hemizygous missense variants were absent in male controls of gnomAD. The two patients with de novo null variants exhibited severe developmental epileptic encephalopathy. While, the patients with hemizygous missense variants had mild focal epilepsy with favorable outcome. Analysis of previously reported cases revealed that males with missense variants presented significantly higher percentage of normal intellectual development and later onset age of seizure than those with null variants, indicating a genotype-phenotype correlation.

CONCLUSION

This study suggested that NEXMIF variants were potentially associated with pure epilepsy with or without intellectual disability. The spectrum of epileptic phenotypes ranged from the mild epilepsy to severe developmental epileptic encephalopathy, where the epileptic phenotypes variability are potentially associated with patients' gender and variant type.

Novel mutation in PARS2 revealed highly variable phenotype of developmental and epileptic encephalopathy-75

BACKGROUND AND AIMS

Biallelic variants in mitochondrial prolyl-tRNA synthetase 2 (PARS2) are associated with developmental and epileptic encephalopathy-75 (DEE75), which is characterized by global developmental delay, seizures and brain imaging anomalies. To date, fewer than 20 patients with PARS2 mutation have been reported in previous literature, and only ten of them had detailed phenotype information.

MATERIALS AND METHODS

In our study, we performed whole exome sequencing for three intellectual disability patients from one family.

RESULTS

Two novel missense PARS2 variants, c.467C>G (p. Pro156Arg) and c.1183G>C (p. Asp395His), were identified. All of our patients displayed profound intellectual disability and absent speech, while other features, including seizures, cardiomyopathy, short stature and brain MRI, varied greatly in this family. This is also the first report of ovarian dysfunction in association with PARS2 mutations.

CONCLUSIONS

We reported three patients with the longest lifespan in reported cases so far, and our results provided an opportunity to study DEE75 prognosis and symptoms in adulthood. Our results further extended the clinical and genetic spectra of PARS2 gene mutation.

Epilepsy in KBG Syndrome: Report of Additional Cases

BACKGROUND

KBG syndrome is a genetic disorder characterized by short stature, dysmorphic features, macrodontia, cognitive impairment, and limb anomalies. Epilepsy is an important comorbidity associated with KBG syndrome, although the entire phenotypic spectrum may not be fully appreciated.

METHODS

We identified five new patients with KBG syndrome-related epilepsy and compared their phenotype to previously reported cases in the literature.

RESULTS

Five patients with KBG syndrome-related epilepsy were identified. Three patients (60%) were male. Median age of seizure onset was 18 months (interquartile range 5, 32). The epilepsy type was generalized in three patients (60%); in two, the epilepsy type was combined (40%), with focal and generalized seizures. In one patient (20%), the epilepsy syndrome was classifiable and the child was diagnosed with myoclonic-atonic epilepsy. All five patients had pathogenic variants in the ANKRD11 gene. Epilepsy was refractory in two patients (40%). No specific antiseizure medication (ASM) was found to be superior. Literature review yielded 134 cases, median age of seizure onset was 4 years, and seizures were generalized (n = 60, 44%), focal (n = 26, 19%), or combined (n = 13, 10%). An epilepsy syndrome was diagnosed in 12 patients (8.8%). In those with documented response to ASM (n = 49), 22.4% were refractory (n = 11).

CONCLUSIONS

Our study confirms that few patients with epilepsy and KBG syndrome have an identifiable epilepsy syndrome and generalized seizures are most common. We highlight that epilepsy associated with KBG syndrome may occur before age one year and should be an important diagnostic consideration in this age group.

What have we learned from the real-world efficacy of FFA in DS and LGS? A post-marketing study in clinical practice

OBJECTIVE

To evaluate the effectiveness and tolerability of fenfluramine (FFA) in routine clinical practice treating real-world populations with Dravet syndrome (DS) and Lennox-Gastaut syndrome (LGS).

METHODS

This was a retrospective analysis of patients with DS or LGS who initiated FFA treatment from 2018 to 2022 at a single center. Patient demographics, medical history, seizure characteristics, and treatment outcomes were collected from electronic medical records. Duration of FFA treatment, dosage regimens, seizure frequency, seizure severity, improvements in cognitive, social, and motor outcomes, and adverse events were extracted and analyzed. Effectiveness was assessed using ≥50 % sustained reduction in monthly seizure frequency vs baseline for ≥2 consecutive months at 12 months; seizure freedom was a secondary measure.

RESULTS

Seizure frequency data was available for 56 of 68 patients included in the study. At 12 months, 50 patients (89.3 %) remained on FFA treatment; 58 % of these patients achieved a ≥50 % sustained response and 10 % experienced seizure freedom. Cognitive, motor, and social improvement were noted in 70.7 %, 36.2 %, and 27.6 % of patients, respectively. The total number of concomitant antiseizure medications was reduced by ≥1 in 29.4 % of patients. No differences were found between DS and LGS patients in these outcomes; age at start of FFA and age at the 12-month timepoint did not have an effect. At least one AE was experienced by 59.7% of patients; in 86.5% of the cases, AEs were plausibly related to treatment. While 70.3% of AEs were self-resolving and 81.8% of the remaining patients experienced mild AEs, 1 patient experienced a serious AE unrelated to FFA which resulted in the patient's death. There were no cases of pulmonary arterial hypertension or ventricular heart disease.

SIGNIFICANCE

The effectiveness and tolerability of FFA treatment in patients with DS or LGS in this retrospective analysis of real-world data were consistent with those seen in randomized clinical trials.

Metabolic causes of pediatric developmental & epileptic encephalopathies (DEE)- genetic variant analysis in a south Indian cohort

PURPOSE

Drug-resistant epilepsy is seen in patients with inborn errors of metabolism and metabolic dysfunction in neurons is crucial to brain disorders associated with psychomotor impairment. Diagnostic rates of metabolic causes of developmental and epileptic encephalopathy (DEE) using next generation sequencing have been rarely studied in literature.

METHODS

A prospective hospital study was carried out in 384 children with DEE, who underwent genetic testing. Metabolic disorders were evaluated with biochemical blood/urine assays and when required CSF estimations performed.

RESULTS

A total of 154 pathogenic/likely pathogenic variants in 384 children were identified. Out of 384 children, 89 were clinically suspected to have probable or possible metabolic disorders. Pathogenic/likely pathogenic variants in metabolic genes were identified in 39 out of 89 (43.8 %) and promising VUS in 28 (31.4 %). These included variants for progressive myoclonus epilepsies (21; 53.8 %), DEE with focal/multifocal seizures (8; 20.5 %), generalized epilepsy (5;12.8 %), early myoclonic encephalopathy (2; 5.1 %), LGS (1; 2.6 %) and West syndrome (2; 5.1 %).

CONCLUSION

Our cohort demonstrates for the first time from the Indian subcontinent that identification of metabolic variants can guide investigations and has therapeutic implications in patients with variable DEE phenotypes. A high utility is noted with regard to diagnosis and prognostication, given the low yield of available biochemical tests, indicating cost-effectiveness of this approach.

GRM7-related disorder: five additional patients from three independent families and review of the literature

Developmental and epileptic encephalopathies (DEEs) refer to a group of severe epileptic syndromes characterized by seizures as well as a developmental delay which can be a consequence of the underlying etiology and/or the epileptic encephalopathy. The genes responsible for DEEs are numerous and their number is increasing since the availability of Next-Generation Sequencing. Pathogenic variants in GRM7, encoding the metabotropic glutamate receptor 7, were recently shown as a cause of a severe DEE with autosomal recessive inheritance. To date, only ten patients have been reported in the literature, generally with severe phenotypes including early-onset epilepsy, microcephaly, brain anomalies, and spasticity. We report here 5 patients from 3 independent families with biallelic variants in the GRM7 gene. We review the literature and provide further elements for the understanding of the genotype-phenotype correlation of this rare syndrome.

ATN1-related infantile developmental and epileptic encephalopathy responding to Ketogenic diet

BACKGROUND

Research has shown gene ATN1 to be associated with the nuclear receptor signaling. Its mutations in an evolutionarily conserved histidine-rich motif may cause CHEDDA, short for congenital hypotonia, epilepsy, developmental delay and digital anomalies, a recently identified neurodevelopmental syndrome that could evolve into developmental and epileptic encephalopathy (DEE). Up to date, there have been reported less than 20 cases, whose clinical features and treatment are worth in-depth exploring.

METHODS

The clinical characteristics and genetic data of an infant with CHEDDA and further DEE were analyzed, who carried a de novo ATN1 variant identified by trio whole-exome sequencing. The alike patients with such a neurodevelopmental syndrome and epileptic seizures were reviewed on the literature.

RESULTS

The infant harboring a de novo missense mutation in ATN1 (c.3155A>C; p.His1052Pro) held almost all features of CHEDDA and presented with drug-resistant epileptic spasms, differing from one case previously reported with the same gene variant exhibiting milder seizures controlled easily. We further reviewed 11 CHEDDA patients with epileptic seizures in the literature and compared the correlation between abnormal cerebral structure and the incidence of intractable epilepsy among CHEDDA patients. Fortunately, this patient's seizures decreased remarkably after administering ketogenic diet (KD).

CONCLUSION

CHEDDA patients have significant phenotypic differences, especially in the epilepsy severity and their drug resistance, even if they carry the same mutation hotspot. Ketogenic diet and other treatments like Topiramate should be recommended for ATN1-related refractory epilepsy based on their regulation on expression of cation-chloride cotransporters and cellular hyperpolarization.

Is tuberous sclerosis complex-associated autism a preventable and treatable disorder?

BACKGROUND

Tuberous sclerosis complex (TSC) is a genetic disorder caused by inactivating mutations in the TSC1 and TSC2 genes, causing overactivation of the mechanistic (previously referred to as mammalian) target of rapamycin (mTOR) signaling pathway in fetal life. The mTOR pathway plays a crucial role in several brain processes leading to TSC-related epilepsy, intellectual disability, and autism spectrum disorder (ASD). Pre-natal or early post-natal diagnosis of TSC is now possible in a growing number of pre-symptomatic infants.

DATA SOURCES

We searched PubMed for peer-reviewed publications published between January 2010 and April 2023 with the terms "tuberous sclerosis", "autism", or "autism spectrum disorder"," animal models", "preclinical studies", "neurobiology", and "treatment".

RESULTS

Prospective studies have highlighted that developmental trajectories in TSC infants who were later diagnosed with ASD already show motor, visual and social communication skills in the first year of life delays. Reliable genetic, cellular, electroencephalography and magnetic resonance imaging biomarkers can identify pre-symptomatic TSC infants at high risk for having autism and epilepsy.

CONCLUSIONS

Preventing epilepsy or improving therapy for seizures associated with prompt and tailored treatment strategies for autism in a sensitive developmental time window could have the potential to mitigate autistic symptoms in infants with TSC.

Severe behavior problems in SYNGAP1-related disorder: A summary of 11 consecutive patients in a tertiary care specialty clinic

SYNGAP1-related disorder (SYNGAP1-RD) is a neurodevelopmental disorder that is commonly associated with epilepsy, autism spectrum disorder (ASD), and disruptive behaviors. In this study, behavior problems in 11 consecutive patients with SYNGAP1-RD are described and quantified based on a behavioral screening conducted within the context of a multi-disciplinary tertiary care specialty clinic visit. The behavioral phenotype was then compared to published samples of behavior problems in ASD and other genetic cause of epilepsy occurring in the context of neurodevelopmental disorders using results from the Aberrant Behavior Checklist-Community (ABC-C), an empirically derived outcome measure. We report common antecedent and consequent events surrounding problem behavior across individuals. Additionally, we report on the management approach of caregivers and the impact of problem behaviors on the family. Our results suggest a number of commonalities between behavioral profiles in SYNGAP1-RD with ASD and other genetic causes of developmental and epileptic encephalopathies, and also highlight severe behavior problems as a specific behavioral phenotype of SYNGAP1-RD.

Lhermitte-Duclos disease with concomitant KCNT2 gene mutation: report of an extremely rare combination

Lhermitte-Duclos disease (LDD) refers to cerebellar dysplastic gangliocytoma, a slow-growing tumor. Pathogenic variants of voltage-gated potassium channels have been associated with epilepsy of variable severity. These include the sodium-activated potassium channel subfamily T member 2 (KCNT2) gene, which encodes for pore-forming alpha subunits. KCNT2 gene mutations have been recently described to cause developmental and epileptic encephalopathies (DEEs). The purpose of the present article is to describe an extremely rare case of a young child who has both LDD and KCNT2 mutation. Our patient is an 11-year-old boy who presented with an absence episode, and his investigations revealed electroencephalography (EEG) abnormalities, LDD, and a heterozygous KCNT2 mutation. Regarding LDD patients, epileptic seizures have been reported in very few cases. Reports of patients with mutated KCNT2 variants are also extremely rare. It is for sure that LDD and KCNT2 mutation is an extremely rare combination. Although further follow-up is mandatory in order to draw safe conclusions for our case, the available data support that our patient is either the first reported case of a subclinical KCNT2 mutation or the first case of its clinical expression in late childhood so far.

Neurochemistry evaluated by magnetic resonance spectroscopy in a patient with FBXO28-related developmental and epileptic encephalopathy

BACKGROUND

Mutations in the FBXO28 gene, which encodes FBXO28, one of the F-box protein family, may cause developmental and epileptic encephalopathy (DEE). FBXO28-related DEE is radiologically characterized by cerebral atrophy, delayed/abnormal myelination, and brain malformation; however, no neurochemical analyses have been reported.

CASE REPORT

A female Japanese infant presented with severe psychomotor delay, epileptic spasms, and visual impairment. Whole-exome sequencing revealed a de novo variant of the FBXO28 gene, leading to the diagnosis of FBXO28-related DEE. Magnetic resonance (MR) spectroscopy at 6, 12, and 32 months revealed decreased N-acetylaspartate and choline-containing compounds and increased levels of myoinositol.

CONCLUSION

MR spectroscopy revealed neurochemical derangement in FBXO28-related DEE, that is, disturbed myelination secondary to neuronal damage with astrogliosis.

Clinical and functional study of two de novo variations of CDKL5 gene

The cyclin-dependent kinase like 5 (CDKL5) gene variation is X-linked dominant and is associated with type 2 developmental and epileptic encephalopathy (DEE). Although numerous cases of CDKL5 have been reported, there is limited discussion regarding functional verification. We described two children with DEE caused by de novo variations of CDKL5 gene, analyzed their clinical manifestations, and performed genetic testing on their gene variation sites. The two cases presented with tonic seizures followed by epileptic spasms, indicative of refractory epilepsy. Physical examination revealed abnormal facial features, including wide eye distance, low nose base, and high nose bridge. Both cases exhibited developmental disabilities. Cranial magnetic resonance imaging (MRI) showed widening of the bilateral frontotemporal extracerebral space. Genetic testing identified variations at the gene sites c.463 + 4A > G (splicing) and c.1854_1861delCAAAGTGA (p.D618Efs*18). Minigene experiments further confirmed that the intronic variation c.463 + 4A > G (splicing) disrupted splicing, leading to protein truncation. CDKL5 gene variation can lead to DEE, and intron variation site c.463 + 4A > G (splicing) can cause protein truncation, which is a pathogenic variation.

De novo variants in PHF21A cause intellectual developmental disorder with behavioral abnormalities and craniofacial dysmorphism with or without seizures: A case report and literature review

PURPOSE

PHF21A has been associated with intellectual developmental disorder with behavioral abnormalities and craniofacial dysmorphism with or without seizures (IDDBCS). Here, we report a new patient with IDDBCS and review previously reported patients.

METHODS

We reviewed the phenotypic and genetic spectrum of the newly diagnosed patient and previously reported patients with IDDBCS.

RESULTS

Among 12 patients (11 whose cases were previously reported and the patient whose case we report here), all patients (100%) had intellectual disability (ID) and motor development delay. Three of 8 patients (37.5%) for whom information on cognition was available had severe ID; ID was moderate in two patients (25%) and mild in three patients (37.5%). Seven of the 12 patients (58.33%) had an epileptic phenotype, and the majority (5/7, 71.42%) of affected individuals developed developmental and epileptic encephalopathy (DEE). Of the 5 patients with DEE, three developed infantile epileptic spasm syndrome (IESS). The seizures of 2 patients (2/5, 40%) were controlled by antiseizure medications. Overgrowth, ADHD, hypotonia, ASD, and sleep disorders were observed in 100%, 77.78%, 70%, 50%, and 33.33% of patients, respectively. All of the variants (100%) were de novo heterozygous variants. Three of the 12 patients (25%) had the same variant (p.Arg580*). The most common types of variants were frameshift variants (7/12, 58.33%), followed by nonsense variants (4/12, 33.33%) and missense variants (1/12, 8.33%). Genotype-phenotype relationships for IDDBCS were uncertain, as phenotypic variability was observed among patients with the same variant (p.Arg580*). The patient whose case we report here had a novel PHF21A gene variant (p.Gln97fs*20), which caused neurodevelopmental delay, macrocephaly, and IESS.

CONCLUSION

The core phenotypes of IDDBCS include neurodevelopmental delay (intellectual disability and impaired motor skills), craniofacial abnormalities, and overgrowth. ADHD, hypotonia, epilepsy, ASD, and sleep disorders are common symptoms of IDDBCS. Notably, DEE is the dominant phenotype of epilepsy, especially IESS. PHF21A may be a candidate gene for DEE. De novo variants are the main mode of inheritance. The most common types of variants are frameshift variants, and the variant p.Arg580* in PHF21A is located at a mutation hot spot.

ARV1 Gene: A Novel Cause of Autosomal Recessive Cerebellar Ataxia with Elevated Alpha Fetoprotein

ARV1 mutation is known to present as developmental and epileptic encephalopathy (DEE)-38. However, the phenotypic spectrum has been expanding ever since it was reported in 2016. Along with seizures and developmental delay, other unique clinical features include ophthalmological abnormalities and movement disorders in the form of ataxia and dystonia, especially in those with missense mutation. These manifestations closely mimic ataxia telangiectasia. Elevation of alpha-fetoprotein levels is an important investigative marker in the diagnosis of ataxia telangiectasia and ataxia with oculomotor apraxia syndromes. ARV1 can also be associated with increased alpha-fetoprotein. There are no reports evaluating alpha-fetoprotein levels in cases with ARV1 mutation, which is significant in the context of ocular abnormalities with ataxia. We report a case of ARV1 mutation presenting with ataxia, ocular abnormalities, and elevated alpha-fetoprotein levels, thus mimicking autosomal recessive cerebellar ataxias. This study provides a comprehensive literature review of the cases reported so far, thus expanding the understanding of the spectrum of presentation, and helps in correlating the clinical picture with the underlying causative genetic mutation. ARV1 gene is another example of one gene with phenotypic pleiotropy. Though presentation with DEE is common, a few, especially those with missense mutations, can present with ataxia and ocular abnormalities. All cases presenting with ataxia who have increased alpha-fetoprotein levels and seizures should be tested for the ARV1 gene, when testing for ataxia genes is negative. The underlying genetic mechanism can explain the varying clinical manifestations of the ARV1 gene.

D-galactose Supplementation for the Treatment of Mild Malformation of Cortical Development with Oligodendroglial Hyperplasia in Epilepsy (MOGHE): A Pilot Trial of Precision Medicine After Epilepsy Surgery

MOGHE is defined as mild malformation of cortical development with oligodendroglial hyperplasia in epilepsy. Approximately half of the patients with histopathologically confirmed MOGHE carry a brain somatic variant in the SLC35A2 gene encoding a UDP-galactose transporter. Previous research showed that D-galactose supplementation results in clinical improvement in patients with a congenital disorder of glycosylation due to germline variants in SLC35A2. We aimed to evaluate the effects of D-galactose supplementation in patients with histopathologically confirmed MOGHE, with uncontrolled seizures or cognitive impairment and epileptiform activity at the EEG after epilepsy surgery (NCT04833322). Patients were orally supplemented with D-galactose for 6 months in doses up to 1.5 g/kg/day and monitored for seizure frequency including 24-h video-EEG recording, cognition and behavioral scores, i.e., WISC, BRIEF-2, SNAP-IV, and SCQ, and quality of life measures, before and 6 months after treatment. Global response was defined by > 50% improvement of seizure frequency and/or cognition and behavior (clinical global impression of "much improved" or better). Twelve patients (aged 5-28 years) were included from three different centers. Neurosurgical tissue samples were available in all patients and revealed a brain somatic variant in SLC35A2 in six patients (non-present in the blood). After 6 months of supplementation, D-galactose was well tolerated with just two patients presenting abdominal discomfort, solved after dose spacing or reduction. There was a 50% reduction or higher of seizure frequency in 3/6 patients, with an improvement at EEG in 2/5 patients. One patient became seizure-free. An improvement of cognitive/behavioral features encompassing impulsivity (mean SNAP-IV - 3.19 [- 0.84; - 5.6]), social communication (mean SCQ - 2.08 [- 0.63; - 4.90]), and executive function (BRIEF-2 inhibit - 5.2 [- 1.23; - 9.2]) was observed. Global responder rate was 9/12 (6/6 in SLC35A2-positive). Our results suggest that supplementation with D-galactose in patients with MOGHE is safe and well tolerated and, although the efficacy data warrant larger studies, it might build a rationale for precision medicine after epilepsy surgery.

Lennox-Gastaut Syndrome: Current Treatments, Novel Therapeutics, and Future Directions

Lennox-Gastaut syndrome is a severe drug-resistant developmental and epileptic encephalopathy with slow spike and wave on EEG (DEE-SSW) composing about 1-2% of epilepsy patients. Seizures in DEE-SSW are caused by a variety of etiologies, and there is a large unmet treatment need as seizures are usually treatment-resistant and individuals are often unable to function independently. The updated definition by the International League Against Epilepsy has established formal diagnostic criteria allowing for more uniform diagnosis. This article provides a review of typical medication management and treatment strategies, including new and developing surgical approaches. Future directions in treatment include expanding genetic testing with the potential for gene therapy and continuously improving surgical options with the goal to prevent progression to DEE-SSW.

A Heterozygous Variant of FGF13 Caused X-Linked Developmental and Epileptic Encephalopathy 90 in a Chinese Family

Developmental and epileptic encephalopathy (DEE) refers to a group of severe epilepsy encephalopathy and development disorders, and its typical clinical features include seizures, drug resistance, and developmental delay or regression. To date, limited studies have reported DEEs driven by FGF13. Here, we reported a girl with developmental and epileptic encephalopathy 90 caused by variant of FGF13. Her electroencephalogram (EEG) showed discontinuous hypsarrhythmia, and a heterozygous nonsynonymous variant in FGF13 [NM_004114.4: c.5C>G, p.(Ala2Gly)] was identified from the proband. The variant was not reported in public databases such as gnomAD and Exome Aggregation Consortium (ExAC), and was predicted to be damaging to proteins and classified as likely pathogenic according to the ACMG guidelines. The seizure was finally controlled by a combination of ACTH + zonisamide (10 mg/kg.d) + levetiracetam (52 mg/kg.d) + clonazepam (0.7 mg/kg.d).

Genotype-phenotype correlations in RHOBTB2-associated neurodevelopmental disorders

PURPOSE

Missense variants clustering in the BTB domain region of RHOBTB2 cause a developmental and epileptic encephalopathy with early-onset seizures and severe intellectual disability.

METHODS

By international collaboration, we assembled individuals with pathogenic RHOBTB2 variants and a variable spectrum of neurodevelopmental disorders. By western blotting, we investigated the consequences of missense variants in vitro.

RESULTS

In accordance with previous observations, de novo heterozygous missense variants in the BTB domain region led to a severe developmental and epileptic encephalopathy in 16 individuals. Now, we also identified de novo missense variants in the GTPase domain in 6 individuals with apparently more variable neurodevelopmental phenotypes with or without epilepsy. In contrast to variants in the BTB domain region, variants in the GTPase domain do not impair proteasomal degradation of RHOBTB2 in vitro, indicating different functional consequences. Furthermore, we observed biallelic splice-site and truncating variants in 9 families with variable neurodevelopmental phenotypes, indicating that complete loss of RHOBTB2 is pathogenic as well.

CONCLUSION

By identifying genotype-phenotype correlations regarding location and consequences of de novo missense variants in RHOBTB2 and by identifying biallelic truncating variants, we further delineate and expand the molecular and clinical spectrum of RHOBTB2-related phenotypes, including both autosomal dominant and recessive neurodevelopmental disorders.

Increased prime edit rates in KCNQ2 and SCN1A via single nicking all-in-one plasmids

BACKGROUND

Prime editing (PE) is the most recent gene editing technology able to introduce targeted alterations to the genome, including single base pair changes, small insertions, and deletions. Several improvements to the PE machinery have been made in the past few years, and these have been tested in a range of model systems including immortalized cell lines, stem cells, and animal models. While double nicking RNA (dncRNA) PE systems PE3 and PE5 currently show the highest editing rates, they come with reduced accuracy as undesired indels or SNVs arise at edited loci. Here, we aimed to improve single ncRNA (sncRNA) systems PE2 and PE4max by generating novel all-in-one (pAIO) plasmids driven by an EF-1α promoter, which is especially suitable for human-induced pluripotent stem cell (hiPSC) models.

RESULTS

pAIO-EF1α-PE2 and pAIO-EF1α-PE4max were used to edit the voltage gated potassium channel gene KCNQ2 and voltage gated sodium channel gene SCN1A. Two clinically relevant mutations were corrected using pAIO-EF1α-PE2 including the homozygous truncating SCN1A R612* variant in HEK293T cells and the heterozygous gain-of-function KCNQ2 R201C variant in patient-derived hiPSC. We show that sncRNA PE yielded detectable editing rates in hiPSC ranging between 6.4% and 9.8%, which was further increased to 41% after a GFP-based fluorescence-activated cell sorting (FACS) cell sorting step. Furthermore, we show that selecting the high GFP expressing population improved editing efficiencies up to 3.2-fold compared to the low GFP expressing population, demonstrating that not only delivery but also the number of copies of the PE enzyme and/or pegRNA per cell are important for efficient editing. Edit rates were not improved when an additional silent protospacer-adjacent motif (PAM)-removing alteration was introduced in hiPSC at the target locus. Finally, there were no genome-wide off-target effects using pAIO-EF1α-PE2 and no off-target editing activity near the edit locus highlighting the accuracy of snc prime editors.

CONCLUSION

Taken together, our study shows an improved efficacy of EF-1α driven sncRNA pAIO-PE plasmids in hiPSC reaching high editing rates, especially after FACS sorting. Optimizing these sncRNA PE systems is of high value when considering future therapeutic in vivo use, where accuracy will be extremely important.

Early life seizures and epileptic spasms in STXBP1-related disorders

Background and Objectives

Individuals with disease-causing variants in STXBP1 frequently have epilepsy onset in the first year of life with a variety of seizure types, including epileptic spasms. However, the impact of early-onset seizures and anti-seizure medication (ASM) on the risk of developing epileptic spasms and impact on their trajectory is poorly understood, limiting informed and anticipatory treatment, as well as trial design.

Methods

We retrospectively reconstructed seizure and medication histories in weekly intervals for individuals with STXBP1-related disorders with epilepsy onset in the first year of life and quantitatively analyzed longitudinal seizure histories and medication response.

Results

We included 61 individuals with early onset seizures, 29 of whom had epileptic spasms. Individuals with neonatal seizures were likely to have continued seizures after the neonatal period (25/26). The risk of developing epileptic spasms was not increased in individuals with neonatal seizures or early infantile seizures (21/41 vs. 8/16; OR 1, 95% CI 0.3-3.9, p = 1). We did not find any ASM associated with the development of epileptic spasms following prior seizures. Individuals with prior seizures (n = 16/21, 76%) had a higher risk to develop refractory epileptic spasms (n = 5/8, 63%, OR =1.9, 95% CI 0.2-14.6, p = 0.6). Individuals with refractory epileptic spasms had a later onset of epileptic spasms (n = 20, median 20 weeks) compared to individuals with non-refractory epileptic spasms (n = 8, median 13 weeks; p = 0.08). When assessing treatment response, we found that clonazepam (n = 3, OR 12.6, 95% CI 2.2-509.4; p < 0.01), clobazam (n=7, OR 3, 95% CI 1.6-6.2; p < 0.01), topiramate (n=9, OR 2.3, 95% CI 1.4-3.9; p < 0.01), and levetiracetam (n=16, OR 1.7, 95% CI 1.2-2.4; p < 0.01) were more likely to reduce seizure frequency and/or to maintain seizure freedom with regards to epileptic spasms than other medications.

Discussion

We provide a comprehensive assessment of early-onset seizures in STXBP1-related disorders and show that the risk of epileptic spasms is not increased following a prior history of early-life seizures, nor by certain ASM. Our study provides baseline information for targeted treatment and prognostication in early-life seizures in STXBP1-related disorders.

The genetic landscape of developmental and epileptic encephalopathy with spike-and-wave activation in sleep

OBJECTIVE

Epileptic Encephalopathy / Developmental Epileptic Encephalopathy with spike-and-wave activation in sleep (EE/DEE-SWAS) is defined as an epilepsy syndrome characterized by neurodevelopmental regression temporally related to the emergence of significant activation of spike-wave discharges in EEG during sleep. The availability of genetic testing has made it evident that monogenic and chromosomal abnormalities play an aetiological role in the development of EE/DEE-SWAS. We sought to review the literature to better understand the genetic landscape of EE/DEE-SWAS.

METHODS

In this systematic review, we reviewed cases of EE/DEE-SWAS associated with a genetic aetiology, collecting information related to the underlying aetiology, onset, management, and EEG patterns.

RESULTS

One hundred and seventy-two cases of EE/DEE-SWAS were identified. Genetic causes of note included pathogenic variants in GRIN2A, ZEB2, CNKSR2 and chromosome 17q21.31 deletions, each of which demonstrated unique clinical characteristics, EEG patterns, and age of onset. Factors identified to raise suspicion of a potential genetic aetiology included the presentation of DEE-SWAS and onset of SWAS under the age of five years. Treatment of EE/DEE-SWAS due to genetic causes was diverse, including a combination of anti-seizure medications, steroids, and other clinical strategies, with no clear consensus on a preferred or superior treatment. Data collected was significantly heterogeneous, with a lack of consistent use of neuropsychology testing, EEG patterns, or use of established clinical definitions.

CONCLUSIONS

Uniformity concerning the new definition of EE/DEE-SWAS, guidelines for management and more frequent genetic screening will be needed to guide best practices for the treatment of patients with EE/DEE-SWAS.

The epileptology of Wiedemann-Steiner syndrome: Electroclinical findings in five patients with KMT2A pathogenic variants

BACKGROUND

Wiedemann-Steiner Syndrome (WSTS) is a rare chromatinopathy caused by pathogenic variants in KMT2A. WSTS is characterized by neurodevelopmental disorders and distinct dysmorphic features. Epilepsy has been reported in only 33 individuals with WSTS, with only limited clinical details described.

METHODS

We identified patients with pathogenic KMT2A variants and epilepsy, and performed thorough phenotyping.

RESULTS

Five patients were identified, all of whom presented with developmental and epileptic encephalopathy (DEE). Epilepsy syndromes observed included Lennox-Gastaut syndrome [2], infantile epileptic spasms syndrome, and DEE with spike-wave activation in sleep. Seizure types observed included absence, generalized tonic-clonic, myoclonic, tonic, atonic, epileptic spasms, and focal seizures.

CONCLUSIONS

The spectrum of epilepsy phenotypes in patients with WSTS can be broad, but presentation is typically severe, usually involving a form of DEE.

Long-term effectiveness of add-on perampanel in patients with Lennox-Gastaut syndrome: a multicenter retrospective study

This retrospective study assessed long-term effectiveness of add-on perampanel (PER) in patients with Lennox-Gastaut syndrome (LGS). Outcomes included time to PER-failure and time to seizure-relapse in responders. Perampanel failure was defined as either discontinuation of PER or initiation of another treatment. Seizure relapse in responders was defined as occurrence of a seizure in seizure-free patients and increase of at least 50% in average monthly seizure frequency for those who were responders. Eighty-seven patients were included. Treatment failure occurred in 52 (59.8%) subjects at a median time of 12 months. Treatment failure was due to lack of efficacy in 27 (52.0%) patients, lack of tolerability in 14 (27.0%), and both reasons in 11 (21.0%). A slower titration was associated with a lower risk of PER failure compared to faster titration schedules and the occurrence of adverse events increased the risk of treatment failure. Thirty-six patients (41.4%) were responders during a median follow-up of 11 months. Seizure relapse occurred in 13/36 (36.1%) patients after a median time of 21 months. The overall rate of seizure responders was 23/87 (26.4%) at the end of follow-up. This study provides real-world evidence about the effectiveness of PER as adjunctive treatment in LGS patients.

Stiripentol for the treatment of seizures associated with Dravet syndrome in patients 6 months and older and taking clobazam

INTRODUCTION

Stiripentol (STP) is a structurally unique molecule with anticonvulsant and neuroprotective properties in animal and human studies. STP enhances gamma-aminobutyric acid (GABA)ergic neurotransmission and inhibits multiple hepatic isoenzymes (i.e. cytochrome P450 system) involved in the metabolism of other antiseizure medications (ASMs) potentiating their anticonvulsant effects and has proven to be a promising therapy in Dravet Syndrome (DS).

AREAS COVERED

The authors review randomized clinical trials and observational studies showing STP efficacy, safety, and tolerability when used as adjunctive therapy with VPA and clobazam in patients with DS. Moreover, they include recent evidence of its use in patients<2 years of age.

EXPERT OPINION

Evidence on STP demonstrates clinically meaningful efficacy in both short and long term in patients with DS. In addition to reducing convulsive seizure frequency, STP also markedly reduces the number of status epilepticus episodes and associated medical complications which are more common in younger children. STP adverse effects are generally not severe and often resolve following STP dose reduction or adjustments of concomitant ASMs. STP is approved by the FDA for children aged 6 months and older with DS who are also taking clobazam, making it the only DS-specific ASM for children under age 1 year.

Before the first seizure: The developmental imprint of infant epilepsy on neurodevelopment

In light of the heterogeneity of epilepsy, both from a clinical and from an etiological perspective, it is difficult to establish a link between epilepsy and development that can be generalized to all infantile epilepsies. In general however, early-onset epilepsy has a poor developmental prognosis that is significantly linked to several parameters: age at first seizure, drug resistance, treatment, and etiology. This paper discusses the relationship between visible epilepsy parameters (those that allow the diagnosis of epilepsy) and neurodevelopment in infants, with special focus on Dravet syndrome and KCNQ2-related epilepsy, two common developmental and epileptic encephalopathies; and focal epilepsy caused by focal cortical dysplasia, which often begins during infancy. There are a number of reasons why it is difficult to dissect the relationship between seizures and their causes, and we suggest a conceptual model in which epilepsy is a neurodevelopmental disorder whose severity is determined by how the disease imprints itself on the developmental process rather than by the symptoms or etiology. The precocity of this developmental imprint may explain why treating seizures once they occur can have a very slight beneficial effect on development.

Relationship Between Epileptic Activity and Developmental Outcome in KCNQ2-Related Epilepsy

BACKGROUND

We aim to describe a cohort of patients with KCNQ2-related epilepsy and evaluate the relationship between epileptic activity and developmental outcome. This topic is relevant for the selection of clinical end points in future clinical trials, since cessation of seizures may or may not be the most important outcome.

METHODS

This retrospective cohort study of children with self-limited (familial) neonatal epilepsy and developmental and epileptic encephalopathy due to pathogenic variants in KCNQ2 was conducted between 2019 and 2021. We collected clinical, therapeutic, and genetic information. Available electroencephalographic recordings were reviewed by a neurophysiologist. Gross motor function was determined using the Gross Motor Function Classification System (GMFCS). The Vineland Adaptive Behavior Composite standard score (ABC SS) was used to measure adaptive functioning.

RESULTS

Among 44 children (mean age 8.1 ± 4.0 years, 45.5% were male), 15 of 44 had S(F)NE, and 29 of 44 had DEE. Delayed seizure freedom was more frequent in DEE than in S(F)NE (P = 0.025), but no correlation was observed between age at seizure freedom and developmental outcome in patients with DEE. Multifocal interictal epileptiform abnormalities at epilepsy onset were more frequent in DEE than in S(F)NE (P = 0.014), and were associated with higher GMFCS (P = 0.027) and lower ABC SS (P = 0.048) in patients with DEE. Disorganized background activity at follow-up was more frequent in DEE than in S(F)NE (P = 0.001), and was associated with higher GMFCS levels (P = 0.009) and lower ABC SS (P = 0.005) in patients with DEE.

CONCLUSIONS

This study shows a partial correlation between epileptic activity and developmental outcome in KCNQ2-related epilepsy.

The burden of illness in Lennox-Gastaut syndrome: a systematic literature review

BACKGROUND

Lennox-Gastaut syndrome (LGS) is a severe developmental and epileptic encephalopathy characterized by drug-resistant epilepsy with multiple seizure types starting in childhood, a typical slow spike-wave pattern on electroencephalogram, and cognitive dysfunction.

METHODS

We performed a systematic literature review according to the PRISMA guidelines to identify, synthesize and appraise the burden of illness in LGS (including "probable" LGS). Studies were identified by searching MEDLINE, Embase and APA PsychInfo, Cochrane's database of systematic reviews, and Epistemonikos. The outcomes were epidemiology (incidence, prevalence or mortality), direct and indirect costs, healthcare resource utilization, and patient and caregiver health-related quality of life (HRQoL).

RESULTS

The search identified 22 publications evaluating the epidemiology (n = 10), direct costs and resource (n = 10) and/or HRQoL (n = 5). No studies reporting on indirect costs were identified. With no specific ICD code for LGS in many regions, several studies had to rely upon indirect methods to identify their patient populations (e.g., algorithms to search insurance claims databases to identify "probable" LGS). There was heterogeneity between studies in how LGS was defined, the size of the populations, ages of the patients and length of the follow-up period. The prevalence varied from 4.2 to 60.8 per 100,000 people across studies for probable LGS and 2.9-28 per 100,000 for a confirmed/narrow definition of LGS. LGS was associated with high mortality rates compared to the general population and epilepsy population. Healthcare resource utilization and direct costs were substantial across all studies. Mean annual direct costs per person varied from $24,048 to $80,545 across studies, and home-based care and inpatient care were significant cost drivers. Studies showed that the HRQoL of patients and caregivers was adversely affected, although only a few studies were identified. In addition, studies suggested that seizure events were associated with higher costs and worse HRQoL. The risk of bias was low or moderate in most studies.

CONCLUSIONS

LGS is associated with a significant burden of illness featuring resistant seizures associated with higher costs and worse HRQoL. More research is needed, especially in evaluating indirect costs and caregiver burden, where there is a notable lack of studies.

Impressive efficacy of the ketogenic diet in a KCNQ2 encephalopathy infant: a case report and exhaustive literature review

BACKGROUND

KCNQ2 encephalopathy is characterized by neonatal-onset epilepsy and developmental impairment, due to "de novo" KCNQ2 pathogenic variants. According to literature data, sodium channel blocking agents appear to be the best treatment options for the disease. Reports describing the use of ketogenic diet (KD) in the KCNQ2 pediatric population are limited. The non-conservative amino acid substitution p.Ser122Leu in KCNQ2 is associated with a broad spectrum of inheritance modalities, clinical phenotypes and outcomes; no previous reports of the same variant treated with KD are available in literature.

CASE DESCRIPTION

We described a 22-month-old female with seizure onset on day 2 of life. At three months of age, she presented refractory status epilepticus (SE) that did not respond to midazolam and carbamazepine, which was added once a "de novo" p.Ser122Leu KCNQ2 variant was demonstrated. KD was the only treatment that led to cessation of seizures. The baby maintained seizures remission and achieved neurodevelopmental milestones.

CONCLUSIONS

To define an overt genotype-phenotype correlation for KCNQ2 pathogenic variants is a challenge; we propose the KD as a valuable treatment for refractory seizures and impaired neurodevelopment in infants harboring "de novo" mutations in the KCNQ2 gene.

Psychometric properties of QI-Disability in CDKL5 Deficiency Disorder: Establishing readiness for clinical trials

CDKL5 Deficiency Disorder (CDD) is a rare genetic disorder with symptoms of epilepsy, developmental impairments, and other comorbidities. Currently, there are no outcome measures for CDD with comprehensive evidence of validation. This study aimed to evaluate the psychometric properties of the Quality of Life Inventory-Disability (QI-Disability) in CDD. Quality of Life Inventory-Disability was administered to 152 parent caregivers registered with the International CDKL5 Disorder Database (ICDD). Confirmatory factor analysis was conducted and the goodness of fit of the factor structure was assessed. Fixed-effects linear regression models examined the responsiveness of QI-Disability to reported changes in child health. A subset of parent caregivers (n = 56) completed QI-Disability, as well as additional health-related questions, on two occasions separated by four weeks to evaluate test-retest reliability. Test-retest reliability was assessed using intra-class correlations (ICCs) calculated from QI-Disability scores. Based upon adjustments for changes in child health, ICCs were recalculated to estimate responsiveness to change. Confirmatory factor analysis, internal consistency, and divergent validity were mostly satisfactory, except divergent validity was not satisfactory for the Social Interactions and Independence domains. The Physical Health, Social Interactions, Leisure, and Total scores responded to changes in the child's Physical health, and the Negative Emotions and Leisure domains responded to changes in the child's behavior. Unadjusted and adjusted ICC values were above 0.8 for the Positive Emotions, Negative Emotions, Social Interactions, Leisure, Independence domains and Total score, and above 0.6 for the Physical Health domain. Findings suggest that QI-Disability is suitable to assess the quality of life of children and adults with CDD and could be of value for upcoming clinical trials.

The neuroimaging spectrum of SLC13A5 related developmental and epileptic encephalopathy

BACKGROUND

SLC13A5 related developmental and epileptic encephalopathy (DEE) is an autosomal recessive condition characterized by neonatal seizures, fever sensitivity, status epilepticus, developmental delay and tooth anomalies. The neuroimaging spectrum of SLC13A5 related DEE is not fully known. We present a case of SLC13A5 related DEE with distinct neuroimaging findings and review the neuroimaging findings of all published cases of SLC13A5 related DEE.

METHODS

A retrospective case review and focused review of the literature was completed.

RESULTS

A 16-month-old male with a clinical phenotype consistent with SLC13A5 related DEE and a previously reported pathogenic variant in SLC13A5, c.655G>A, p.Gly219Arg and a novel likely pathogenic variant in SLC13A5, c.202C>T, p.Pro68Ser was identified. MRI at day 5 of life revealed wide spread punctate white matter lesions (PWMLs) affecting the subcortical white matter, periventricular white matter, splenium of the corpus callosum, posterior limb of the internal capsule, corticospinal tracts, midbrain, pons and medulla, mimicking a metabolic/infectious etiology. MRI at one month showed atrophy and evolution of white matter necrosis. One hundred and five cases of SLC13A5 related DEE were identified. Initial MRI was completed in 62 cases (59%). MRI was normal in 41 cases (66%) and abnormal in 21 (34%). White matter abnormalities were most common (n=15, 71%); PWMLs occurred in 8 cases (38%).

CONCLUSION

Neuroimaging abnormalities may exist in a third of SLC13A5 related DEE cases. White matter abnormalities such as PWMLs appear most common. It remains unknown why some are susceptible to these lesions and how they affect long-term neurodevelopmental outcomes in SLC13A5 related DEE.

SCN1A as a therapeutic target for Dravet syndrome

INTRODUCTION

Dravet syndrome is a severe early infancy-onset developmental and epileptic encephalopathy. Patients have drug-resistant seizures, as well as significant co-morbidities, including developmental impairment, crouch gait, sleep disturbance, and early mortality. The underlying cause is mutations in SCN1A, encoding the sodium channel subunit NaV1.1, in >90% of patients. At present, approved Dravet syndrome treatments are symptomatic, primarily aimed at reducing seizure frequency, but having little to no effect on co-morbidities.

AREAS COVERED

We discuss the potential to treat Dravet syndrome by targeting NaV1.1 directly. Anti-seizure medications that act as sodium channel inhibitors are generally minimally effective and can actually exacerbate seizures. However, other interventions are currently under investigation, including gene therapies that increase the amount of functional NaV1.1. Some of these interventions have encouraging pre-clinical data from in vitro and animal models.

EXPERT OPINION

Increasing functional NaV1.1 via antisense oligonucleotides or virus-borne vectors is the most promising avenue for meaningful improvement in Dravet syndrome treatment, with the potential to not only reduce seizures but also address the multiple co-morbidities associated with this disease. However, human clinical trial data are necessary to determine safety and to clarify if, and to what extent, these interventions modify the natural history of Dravet syndrome.

ATP1A3-related early childhood onset developmental and epileptic encephalopathy responding to corpus callosotomy: A case report

BACKGROUND

VariousATP1A3variant-related diseases have been reported, including alternating hemiplegia of childhood; rapid-onset dystonia-parkinsonism; and cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss syndrome. Moreover, a few cases of developmental and epileptic encephalopathy (DEE) with none of these symptoms have been reported. Here, we present a case of DEE with early childhood onset caused by anATP1A3variant that was effectively treated using corpus callosotomy (CC).

CASE PRESENTATION

At the age of 3 years, the patient developed epileptic spasms, complicated by generalized and focal aware tonic seizures. Based on the seizure type and electroencephalographic findings showing a generalized spike and waves as well as interictal left frontal-dominant spikes, combined generalized and focal epilepsy was diagnosed. Whole-exome sequencing revealed a de novo missense variant inATP1A3(c.2888G > A, p.Gly963Asp), which was classified as likely pathogenic. At the age of 5 years, CC for generalized tonic seizures resulted in seizure-freedom using two anti-seizure medications. Subsequently, the patient achieved better verbal development.

DISCUSSION AND CONCLUSION

Early childhood onset DEE has not been reported in patients with ATP1A3 variants. Moreover, CC was extremely effective in our case. Although more research is needed to determine the etiology of epilepsy caused by theATP1A3 variant, the clinical course of DEE caused by the ATP1A3 variant is diverse and its prognosis may be improved in early childhood onset cases using aggressive control of epilepsy, such as CC.

GNAO1-related neurodevelopmental disorder: Literature review and caregiver survey

Background

GNAO1-related neurodevelopmental disorder is a heterogeneous condition characterized by hypotonia, developmental delay, epilepsy, and movement disorder. This study aims to better understand the spectrum of epilepsy associated with GNAO1 variants and experience with anti-seizure medications, and to review published epilepsy phenotypes in GNAO1.

Methods

An online survey was distributed to caregivers of individuals diagnosed with GNAO1 pathogenic variants, and a literature review was conducted.

Results

Fifteen respondents completed the survey with the median age of 39 months, including a novel variant p.Q52P. Nine had epilepsy - six had onset in the first week of life, three in the first year of life - but two reported no ongoing seizures. Seizure types varied. Individuals were taking a median of 3 seizure medications without a single best treatment. Our cohort was compared to a literature review of epilepsy in GNAO1. In 86 cases, 38 discrete variants were described; epilepsy is reported in 53 % cases, and a developmental and epileptic encephalopathy in 36 %.

Conclusions

While GNAO1-related epilepsy is most often early-onset and severe, seizures may not always be drug resistant or lifelong. Experience with anti-seizure medications is varied. Certain variant "hotspots" may correlate with epilepsy phenotype though genotype-phenotype correlation is poorly understood.

Novel homozygous AP3B2 mutations in four individuals with developmental and epileptic encephalopathy: A rare clinical entity

OBJECTIVES

Developmental and epileptic encephalopathies (DEEs) are heterogeneous severe neurodevelopmental disorders characterized by recurrent clinical seizures that begin in the neonatal period and early childhood and regression or delay in cognitive, sensory and motor skills in the context of accompanying epileptiform abnormalities. Adaptor-related protein complex 3 beta-2 subunit (AP3B2) gene variants are thought to cause disruption of neuron-specific neurotransmitter release.

METHODS

In this case report, whole exome sequencing (WES) was performed on two of the four pediatric patients who came from two unrelated families and were affected by DEE. As a result of WES, previously unreported variants, that is, p.Ala149Serfs* 34 and p.Pro993Argfs* 5, were detected in the AP3B2 gene. These variants were studied using Sanger sequencing in the siblings affected by DEE of the said pediatric patients and in their healthy parents.

RESULTS

Autosomal recessive variants of the AP3B2 are associated with the development of DEE. To date, only 14 cases of AP3B2 mutations have been reported in the literature. Consequentially, DEE phenotype involving severe global developmental delay emerged, which is characterized by early-onset infantile epileptic encephalopathy, severe hypotonia, postnatal microcephaly, poor eye contact, speech retardation, abnormal involuntary movements, stereotypical hand movements, progressive intellectual disability, and behavioral and neuropsychiatric findings.

CONCLUSION

Given the limited number of patients reported in the literature, detailed studies of the specific clinical and molecular features of AP3B2 gene variants, will shed light on the genotype-phenotype correlation.

A case of ALG11-congenital disorders of glycosylation diagnosed by post-mortem whole exome sequencing

INTRODUCTION

Congenital disorders of glycosylation (CDG) are inherited inborn errors of metabolism due to abnormal protein and lipid glycosylation that present with multi-systemic manifestations. The heterogeneity of CDG poses a serious diagnostic challenge; therefore, whole-exome sequencing (WES), which plays an increasingly important role in the molecular diagnosis of CDG, is used for examining patients with CDG.

CASE REPORT

We report the case of a two-month-old male patient who developed developmental and epileptic encephalopathy (DEE) with intractable seizures and microcephaly. EEG demonstrated a suppression-burst (S-B) pattern, and MRI showed delayed myelination and progressive atrophic changes. Although CDG was clinically suspected, serum transferrin isoelectric focusing analysis appeared to be normal. The patient died by six years of age. Postmortem WES performed approximately 20 years after the patient's death revealed homozygous variants in ALG11 (NM_001004127.3: c.935A > C, p.Glu312Ala), and the patient was diagnosed with ALG11-CDG.

CONCLUSION

We present a case of the patient with ALG11-CDG diagnosed using post-mortem WES. The EEG revealed a S-B pattern that indicated severely drug-resistant DEE, which was associated with poor prognosis. If a CDG is suspected, WES should be considered.

Exploring the genetic etiology of drug-resistant epilepsy: incorporation of exome sequencing into practice

BACKGROUND

By affecting about 50 million people worldwide, epilepsy is considered a global concern in neurology. Intolerable enough, up to ¼ of all patients do not respond to antiepileptic drugs and have recurring seizures. Therefore, revealing the underlying etiology is quite demanding in a clinical context to improve diagnosis and disease management.

METHODS

Initially, 85 patients suspected of epilepsy underwent thorough clinical and paraclinical evaluation and 24 individuals with drug-resistant epilepsy entered the study. Using whole-exome sequencing, the genetic etiology of drug-resistant epilepsy was investigated and discerned whether this method could facilitate the management of drug-resistant epilepsy through personalized medicine. Eventually, functional annotation was performed and drug-gene interaction networks were constructed to find potential therapeutic targets.

RESULTS

We found eleven novel variants in various genes including IRF2BPL, ST3GAL3, and GPAA1, for which a few epilepsy-related variants are available in public databases. The overall diagnostic yield for likely pathogenic and pathogenic variants and the detection rate of novel variants were 25% and 84.6%, respectively. Based on the results, two patients were considered potential candidates for personalized medicine. The highest number of interaction with drugs was demonstrated for SCN1A, SCN2A, and GRIN2A genes.

CONCLUSIONS

This study highlighted the importance of consanguineous marriage in drug-resistant epilepsy and suggested the possibility of reduced penetrance and variable expressivity in some of the autosomal dominant cases. We also suggest that whole-exome sequencing could facilitate personalized management of drug-resistant epilepsy. Regarding drug-gene interactions, some genes such as SCN1A and SCN2A might serve as therapeutic targets in drug-resistant epilepsy.

Investigation of novel de novo KCNC2 variants causing severe developmental and early-onset epileptic encephalopathy

Purpose The voltage-gated potassium channel K_v3.2, encoded by KCNC2, facilitates fast-spiking GABAergic interneurons to fire action potentials at high frequencies. It is pivotal to maintaining excitation/inhibition balance in mammalian brains. This study identified two novel de novo KCNC2 variants, p.Pro470Ser (P470S) and p.Phe382Leu (F382L), in patients with early onset developmental and epileptic encephalopathy (DEE). Methods To examine the molecular basis of DEE, we studied the functional characteristics of variant channels using patch-clamp techniques and computational modeling. Results Whole-cell patch clamp recordings from infected HEK293 cells revealed that channel activation and deactivation kinetics strongly decreased in both K_v3.2 P470S and F382L variant channels. This decrease also occurred in K_v3.2 p.Val471Leu (V471L) channels, known to be associated with DEE. In addition, K_v3.2 F382L and V471L variants exhibited a significant increase in channel conductance and a ∼20 mV negative shift in the threshold for voltage-dependent activation. Simulations of model GABAergic interneurons revealed that all variants decreased neuronal firing frequency. Thus, the variants' net loss-of-function effects disinhibited neural networks. Conclusion Our findings provide compelling evidence supporting the role of KCNC2 as a disease-causing gene in human neurodevelopmental delay and epilepsy.

Neurochemistry evaluated by MR spectroscopy in a patient with SPTAN1-related developmental and epileptic encephalopathy

BACKGROUND

Mutation of the SPTAN1 gene, which encodes α-fodrin (non-erythrocyte α-II spectrin), is one of the causes of developmental and epileptic encephalopathies (DEEs). SPTAN1-related DEE is radiologically characterized by cerebral atrophy, especially due to white matter volume reduction, hypomyelination, pontocerebellar hypoplasia, and a thin corpus callosum, however, no neurochemical analysis has been reported.

CASE REPORT

A Japanese infant female presented with severe psychomotor delay, tonic spasms, and visual impairment. Whole-exome sequencing revealed a de novo variant of the SPTAN1 gene, leading to a diagnosis of SPTAN1-related DEE. MR spectroscopy at ages 5 months, 11 months, and 1 year and 4 months revealed decreased N-acetylaspartate and choline-containing compounds, and increased glutamate or glutamine.

CONCLUSION

The decreased concentrations of N-acetylaspartate and choline-containing compounds may have resulted from neuroaxonal network dysfunction and hypomyelination, respectively. The increased glutamate or glutamine may have reflected a disrupted glutamate-glutamine cycle caused by dysfunction of exocytosis, in which α-fodrin plays an important role. MR spectroscopy revealed neurochemical derangement in SPTAN1-related DEE, which may be a possible pathomechanism and will be useful for its diagnosis.

Genetics and gene therapy in Dravet syndrome

Dravet syndrome is a well-established electro-clinical condition first described in 1978. A main genetic cause was identified with the discovery of a loss-of-function SCN1A variant in 2001. Mechanisms underlying the phenotypic variations have subsequently been a main topic of research. Various genetic modifiers of clinical severities have been elucidated through many rigorous studies on genotype-phenotype correlations and the recent advances in next generation sequencing technology. Furthermore, a deeper understanding of the regulation of gene expression and remarkable progress on genome-editing technology using the CRISPR-Cas9 system provide significant opportunities to overcome hurdles of gene therapy, such as enhancing Na_V1.1 expression. This article reviews the current understanding of genetic pathology and the status of research toward the development of gene therapy for Dravet syndrome. This article is part of the Special Issue "Severe Infantile Epilepsies".

SYNGAP1-related developmental and epileptic encephalopathy: The impact on daily life

SYNGAP1-developmental and epileptic encephalopathy (SYNGAP1-DEE) has been recently featured as a distinct genetic disease characterized by global psychomotor delay mainly involving language, moderate-to-severe cognitive impairment, autism spectrum disorder, and a generalized epilepsy with spontaneous and reflex seizures. The severity and variability of function impairment and the impact on patients' and caregivers' daily life are still poorly acknowledged. The SYNGAP1 Italian Family Association developed a survey, shared online with caregivers, exploring several issues, including: epilepsy outcome, comorbidities, daily-living skills, hospitalizations, rehabilitation treatments, economic burden, and COVID-19 pandemic impact. Caregivers of 13 children and adolescents participated in the survey. They most often show a fine and gross-motor impairment and a drug-resistant epilepsy with possibility to experience pluridaily absence seizures that may lead to periods of psychomotor regressions. Eating and sleep problems are reported in the majority. Most parents are concerned about language impairment, behavioral issues and lack of autonomy in daily-living activities. Specific neuropsychological evaluations for autism should be early considered in order to identify intervention strategies involving alternative communication strategies, which can positively affect behavior and quality of life. Rehabilitation treatment should aim to the acquisition and consolidation of personal autonomy.

Adaptive behavior and psychiatric comorbidities in KCNB1 encephalopathy

AIM

KCNB1 encephalopathy encompasses a broad phenotypic spectrum associating intellectual disability, behavioral disturbances, and epilepsies of various severity. Using standardized parental questionnaires, we aimed to capture the heterogeneity of the adaptive and behavioral features in a series of patients with KCNB1 pathogenic variants.

METHODS

We included 25 patients with a KCNB1 encephalopathy, aged from 3.2 to 34.1 years (median = 10 years). Adaptive functioning was assessed in all patients using the French version of the Vineland Adaptive Behavior Scales, Second Edition (VABS-II) questionnaire. We screened global behavior with the Childhood Behavioral Check-List (CBCL, Achenbach) and autism spectrum disorder (ASD) with the Social Communication Questionnaire (SCQ). We used a cluster analysis to identify subgroups of adaptive profiles.

RESULTS

VABS-II questionnaire showed pathological adaptive behavior in all participants with a severity of adaptive deficiency ranging from mild in 8/20 to severe in 7/20. Eight out of 16 were at risk of Attention Problems at the CBCL and 13/18 were at risk of autism spectrum disorder (ASD). The adaptive behavior composite score significantly decreased with age (Spearman's Rho=-0.72, p<0.001) but not the equivalent ages, suggesting stagnation and slowing but no regression over time. The clustering analysis identified two subgroups of patients, one showing more severe adaptive behavior. The severity of the epilepsy phenotype predicted the severity of the behavioral profile with a sensitivity of 70% and a specificity of 90.9%.

CONCLUSION

This study confirms the deleterious consequences of early-onset epilepsy in addition to the impact of the gene dysfunction in patients with KCNB1 encephalopathy. ASD and attention disorders are frequent. Parental questionnaires should be considered as useful tools for early screening and care adaptation.

L-Serine Treatment is Associated with Improvements in Behavior, EEG, and Seizure Frequency in Individuals with GRIN-Related Disorders Due to Null Variants

Pathogenic missense variants in GRIN2A and GRIN2B may result in gain or loss of function (GoF/LoF) of the N-methyl-D-aspartate receptor (NMDAR). This observation gave rise to the hypothesis of successfully treating GRIN-related disorders due to LoF variants with co-agonists of the NMDAR. In this respect, we describe a retrospectively collected series of ten individuals with GRIN2A- or GRIN2B-related disorders who were treated with L-serine, each within an independent n-of-1 trial. Our cohort comprises one individual with a LoF missense variant with clinical improvements confirming the above hypothesis and replicating a previous n-of-1 trial. A second individual with a GoF missense variant was erroneously treated with L-serine and experienced immediate temporary behavioral deterioration further supporting the supposed functional pathomechanism. Eight additional individuals with null variants (that had been interpreted as loss-of-function variants despite not being missense) again showed clinical improvements. Among all nine individuals with LoF missense or null variants, L-serine treatment was associated with improvements in behavior in eight (89%), in development in four (44%), and/or in EEG or seizure frequency in four (44%). None of these nine individuals experienced side effects or adverse findings in the context of L-serine treatment. In summary, we describe the first evidence that L-serine treatment may not only be associated with clinical improvements in GRIN-related disorders due to LoF missense but particularly also null variants.

Genetic testing before epilepsy surgery - An exploratory survey and case collection from German epilepsy centers

INTRODUCTION

Genetic testing in people with epilepsy may support presurgical decision-making. It is currently unclear to what extent epilepsy centres use genetic testing in presurgical evaluation.

METHODS

We performed an exploratory survey among members of the German Society for Epileptology to study the current practice of genetic testing in presurgical evaluation at the respective sites. Survey participants contributed educational case reports.

RESULTS

The majority of participants consider genetic testing to be useful in individuals with familial syndromes or phenotypic features suggesting a genetic etiology. We report 25 cases of individuals with a confirmed genetic diagnosis that have previously undergone epilepsy surgery. Our cases demonstrate that a genetic diagnosis has an impact on both the decision-making process during presurgical evaluation, as well as the postoperative outcome.

CONCLUSION

Genetic testing as part of the presurgical work-up is becoming increasingly established in epilepsy centres across Germany. mTORopathies and genetic hypothalamic hamartomas seem to be associated with a generally favourable surgical outcome. Synaptopathies and channelopathies may be associated with a worse outcome and should be considered on a case-by-case level. Prospective studies are needed to examine the impact of an established genetic diagnosis on postsurgical outcome.

A SCN8A variant associated with severe early onset epilepsy and developmental delay: Loss- or gain-of-function?

SCN8A, encoding the voltage-gated sodium channel subunit Na_V1.6, has been associated with a wide spectrum of neuropsychiatric disorders. Missense variants in SCN8A which increase the channel activity can cause a severe developmental and epileptic encephalopathy (DEE). One DEE variant (p.(Arg223Gly)) was described to cause a predominant loss-of-function (LOF) mechanism when expressed in neuroblastoma cells, which is not consistent with the genotype-phenotype correlations in this gene. To resolve this discrepancy and understand the pathophysiological mechanism of this variant, we performed comprehensive electrophysiological studies in both neuroblastoma cells and primary hippocampal neuronal cultures. Although we also found that p.(Arg223Gly) significantly decreased Na⁺ current density and enhanced fast inactivation compared to the wild type (WT) channel in transfected neuroblastoma cells (both LOF mechanisms), it also caused a strong hyperpolarizing shift of steady-state activation and accelerated the recovery from fast inactivation (both gain-of-function (GOF) mechanisms). In cultured neurons transfected with mutant vs. WT Na_V1.6 channels, we found more depolarized resting membrane potentials and a decreased rheobase leading to enhanced action potential firing. We conclude that SCN8A p.(Arg223Gly) leads to a net GOF resulting in neuronal hyperexcitability and a higher firing rate, fitting with the central role of GOF mechanisms in DEE.

Developmental and epilepsy spectrum of Poirier-Bienvenu neurodevelopmental syndrome: Description of a new case study and review of the available literature

AIM

To better characterize the clinical phenotype of Poirier-Bienvenu neurodevelopmental syndrome (OMIM ID: 618,732) due to pathogenic variants of the CSNK2B gene.

METHOD

We reviewed the electro-clinical and developmental data of all 14 patients with de novo mutations of the CSNK2B gene reported in the literature and describe a further individual with a novel CSNK2B pathogenic variant.

RESULTS

Clustered generalized tonic-clonic or myoclonic seizures with onset before the age of 18 months and delayed neurodevelopment were present in more than 75% of patients. Epilepsy was pharmaco-resistant in 40%. All the individuals (27%) with normal neurological development had pharmaco-sensitive epilepsy. The severity of cognitive and motor impairments was higher in the group with pharmaco-resistant epilepsy, and a statistically significant correlation between seizure control and the severity of cognitive impairment was documented (χ2(3) = 9.44; p = .024) INTERPRETATION: Early seizure onset, clustered seizures and delayed development in both males and females were early clinical markers in most patients with CSNK2B mutations. The entity of neurodevelopmental abnormalities was related to epilepsy severity. Prospective studies are required to better assess the relationship between epilepsy and developmental outcomes in this condition.

A retrospective analysis of memantine use in a pediatric neurology clinic

BACKGROUND

Memantine is an N-methyl-D-aspartate receptor (NMDA-R) antagonist, approved for dementia, but also studied in pediatric autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD).

METHODS

We reviewed children treated with memantine in a single-centre pediatric neurology clinic. Clinical data extracted included age, sex, weight, clinical history, reason for memantine prescription, period of treatment trial and dosage, treatment response, side effects, and concomitant medications.

RESULTS

Eight patients met inclusion criteria with diagnoses including developmental and epileptic encephalopathy, focal epilepsy, ASD, ADHD. Four reported clear cognitive improvement, though two of these started other concurrent treatments at the time of memantine initiation. One of three patients with poorly-controlled epilepsy, a girl with a GRIN2A variant of uncertain significance, had a clear reduction in seizure frequency. No serious adverse events were noted.

CONCLUSIONS

Memantine is generally well-tolerated in children, and may have potential benefit for a broad range of pediatric neurodevelopmental disorders.

Biallelic mutations in ELFN1 gene associated with developmental and epileptic encephalopathy and joint laxity

ELFN1, a transmembrane leucine rich repeat protein, is involved in signal transduction in both neural cells and ROD ON-bipolar synaptogenesis. We present three siblings with developmental and epileptic encephalopathy and co-morbidities due to ELFN1 gene mutation; this is the first report in literature defining the human phenotype of ELFN1 gene mutation. Clinical, electrophysiological, and radiological findings along with comprehensive genetic studies of the patients and their family members are presented. Developmental and epileptic encephalopathy, autistic features, pyramidal signs, joint laxity, and dysmorphic features are the characteristic findings of this new clinical entity, involving mainly nervous system and possibly connective tissue. Whole exome sequence analysis followed by Sanger sequencing in all family members revealed disease-causing 8 bp frameshift mutation depicted as NM_001128636.2: c.42_49delGGCCGCCA; p. (Ala15Profs*241) in ELFN1. The variant, located in the signal peptide domain in the ELFN1 gene, was found to be homozygous in three patients, and heterozygous in the parents and three healthy siblings. Segregation analysis in family members together with pathogenicity assessment tools strongly supported the damaging effect of the frameshift variant on the function of the ELFN1 protein. Mutations in ELFN1 gene may be considered in patients with neonatal and infantile-onset epileptic encephalopathy before the full clinical picture is apparent.

Treatment with fenfluramine in patients with Dravet syndrome has no long-term effects on weight and growth

OBJECTIVE

Appetite disturbance and growth abnormalities are commonly reported in children with Dravet syndrome (DS). Fenfluramine (Fintepla) has demonstrated profound reduction in convulsive seizure frequency in DS and was recently approved for use in DS in the US and EU. Prior to its use in epilepsy, fenfluramine was approved to suppress appetite in obese adults. Here, we evaluated the impact of fenfluramine on weight and growth in patients with DS treated for ≥12 months or ≥24 months and compared the results with growth curves in normative reference populations and published historical controls among patients with DS.

METHODS

Historical control data from a recent study of 68 patients with DS show decreases in height and weight Z-scores of ∼0.1 standard deviation (SD) for every 12-month increase in age (Eschbach K. Seizure. 2017;52:117-22). Anthropometric data for fenfluramine were extracted from an open-label extension (OLE) study of eligible patients with DS (2-18 y/o; fenfluramine dose: 0.2-0.7 mg/kg/day). Z-score analyses were based on the Boston Children's Hospital algorithm and assessed potential impact of fenfluramine on growth at OLE baseline, at Month 12, and at Month 24. A mixed-effect model for repeated measures (MMRM) estimated changes in height and weight over time. Height and weight Z-scores were also analyzed by dose group (0.2-<0.3 mg/kg/day, 0.3-<0.5 mg/kg/day, and 0.5-0.7 mg/kg/day), averaged over time.

RESULTS

At the time of analysis, 279 patients were treated with fenfluramine for ≥12 months; 128 were treated for ≥24 months. Relative to the reference population with DS, fenfluramine treatment for ≥12 months or for ≥24 months had minimal impact on height or weight over time as assessed by Z-score analyses. No substantial dose-dependent changes from baseline were observed at Month 12 nor at Month 24. MMRM showed that patients treated with fenfluramine for ≥12 months (N = 262) had an estimated change in Z-score per year of -0.056 for height and -0.166 for weight. For patients with data from all three time points (baseline, 12 months, and 24 months; N = 110), estimated changes in Z-scores per year were -0.025 for height and -0.188 for weight. MMRM projections based on normative reference growth curves were comparable to growth data from historical control populations with DS.

SIGNIFICANCE/CONCLUSION

Long-term treatment with fenfluramine had minimal impact on the growth of patients with DS as demonstrated by differences in Z-scores for height and weight at 12 months and at 24 months. Changes in Z-scores for height and weight were consistent with published reports on patients with DS.