Early-onset Epileptic Encephalopathy Research Articles

Epileptic Encephalopathy of Unknown Cause in Turkey Indicates a New Homozygous <i>NAPB </i>Gene Variant

<b><i>Introduction:</i></b> As with many genetic diseases, the diagnostic role of next-generation sequencing is invaluable for early-onset epileptic encephalopathies. SNARE proteins in synaptic vesicles (synaptobrevin-2) and synaptic plasma membrane (syntaxin-1, SNAP-25) are involved in synaptic exocytosis and recycling. <b><i>Patient Presentation:</i></b> Here, we report a patient that started in early childhood with seizures resistant to antiepileptic drugs, then developed epileptic encephalopathy. <b><i>Discussion/Conclusion:</i></b> The <i>NAPB </i>gene encodes proteins in the SNARE complex. A previously unidentified homozygous missense variant in the <i>NAPB </i>gene may have contributed significantly to the etiology of our patient with epileptic encephalopathy. We also summarize the clinical, radiological, laboratory, and genetic findings of previously published patients with NAPB variants.

A novel pathogenic SLC12A5 missense variant in epilepsy of infancy with migrating focal seizures causes impaired KCC2 chloride extrusion.

The potassium-chloride co-transporter 2, KCC2, is a neuron-specific ion transporter that plays a multifunctional role in neuronal development. In mature neurons, KCC2 maintains a low enough intracellular chloride concentration essential for inhibitory neurotransmission. During recent years, pathogenic variants in the KCC2 encoding gene SLC12A5 affecting the functionality or expression of the transporter protein have been described in several patients with epilepsy of infancy with migrating focal seizures (EIMFS), a devastating early-onset developmental and epileptic encephalopathy. In this study, we identified a novel recessively inherited SLC12A5 c.692G>A, p. (R231H) variant in a patient diagnosed with severe and drug-resistant EIMFS and profound intellectual disability. The functionality of the variant was assessed in vitro by means of gramicidin-perforated patch-clamp experiments and ammonium flux assay, both of which indicated a significant reduction in chloride extrusion. Based on surface immunolabeling, the variant showed a reduction in membrane expression. These findings implicate pathogenicity of the SLC12A5 variant that leads to impaired inhibitory neurotransmission, increasing probability for hyperexcitability and epileptogenesis.

RARS1-related hypomyelinating leukodystrophy-9 (HLD-9) in two distinct Iranian families: Case report and literature review.

Hypomyelinating leukodystrophy-9 (HLD-9) is caused by biallelic pathogenic variants in RARS1, which codes for the cytoplasmic tRNA synthetase for arginine (ArgRS). This study aims to evaluate the clinical, neuroradiological, and genetic characteristics of patients with RARS1-related disease and determine probable genotype-phenotype relationships. We identified three patients with RARS1 homozygous pathogenic variants. Furthermore, we performed a comprehensive review of the literature. Homozygous variants of RARS1 (c.2T>C (p.Met1Thr)) were identified in three patients with HLD-9. Clinical symptoms were severe in all patients. Following the literature review, thirty HLD-9 cases from eight studies were found. The 33 patients' main symptoms were hypomyelination, language delay, and intellectual disability or developmental delay. The mean age of onset for HLD9 in the group of 33 patients with a known age of onset was 5.8 months (SD = 8.1). The interquartile range of age of onset was 0-10 months. Of the 25 variants identified, c.5A>G (p.Asp2Gly) was identified in 11 patients. Pathogenic variants in RARS1 decrease ArgRS activity and cause a wide range of symptoms, from severe, early onset epileptic encephalopathy with brain atrophy to a mild condition with relatively maintained myelination. These symptoms include the classic hypomyelination presentation with nystagmus and spasticity. Furthermore, the pathogenicity of the variation c.2T>C (p.Met1Thr) has been shown.

Early onset epileptic and developmental encephalopathy and MOGS variants: a new diagnosis in the whole exome sequencing (WES) ERA : Report of a new patient and review of the literature.

Mannosyl-oligosaccharide glucosidase - congenital disorder of glycosylation (MOGS-CDG) is determined by biallelic mutations in the mannosyl-oligosaccharide glucosidase (glucosidase I) gene. MOGS-CDG is a rare disorder affecting the processing of N-Glycans (CDG type II) and is characterized by prominent neurological involvement including hypotonia, developmental delay, seizures and movement disorders. To the best of our knowledge, 30 patients with MOGS-CDG have been published so far. We described a child who is compound heterozygous for two novel variants in the MOGS gene. He presented Early Infantile Developmental and Epileptic Encephalopathy (EI-DEE) in the absence of other specific systemic involvement and unrevealing first-line biochemical findings. In addition to the previously described features, the patient presented a Hirschprung disease, never reported before in individuals with MOGS-CDG.

Clinical and molecular characterization of patients with YWHAG-related epilepsy.

YWHAG variant alleles have been associated with a rare disease trait whose clinical synopsis includes an early onset epileptic encephalopathy with predominantly myoclonic seizures, developmental delay/intellectual disability, and facial dysmorphisms. Through description of a large cohort, which doubles the number of reported patients, we further delineate the spectrum of YWHAG-related epilepsy. We included in this study 24 patients, 21 new and three previously described, with pathogenic/likely pathogenic variants in YWHAG. We extended the analysis of clinical, electroencephalographic, brain magnetic resonance imaging, and molecular genetic information to 24 previously published patients. The phenotypic spectrum of YWHAG-related disorders ranges from mild developmental delay to developmental and epileptic encephalopathy (DEE). Epilepsy onset is in the first 2 years of life. Seizure freedom can be achieved in half of the patients (13/24, 54%). Intellectual disability (23/24, 96%), behavioral disorders (18/24, 75%), neurological signs (13/24, 54%), and dysmorphisms (6/24, 25%) are common. A genotype-phenotype correlation emerged, as DEE is more represented in patients with missense variants located in the ligand-binding domain than in those with truncating or missense variants in other domains (90% vs. 19%, p < .001). This study suggests that pathogenic YWHAG variants cause a wide range of clinical presentations with variable severity, ranging from mild developmental delay to DEE. In this allelic series, a genotype-phenotype correlation begins to emerge, potentially providing prognostic information for clinical management and genetic counseling.

[Clinical features and genetic analysis of five children with epilepsies due to variants of SCN8A gene].

To explore the clinical and genetic characteristics of five children with epilepsies due to variants of SCN8A gene. Clinical data of five children (four males and one female) admitted to Linyi People's Hospital due to hereditary epilepsies between August 2015 and August 2022 were collected. Whole exome sequencing was carried out for these children, and candidate variants were verified by Sanger sequencing. All of the five children were found to harbor variants of the SCN8A gene. Case 1, who had benign familial infantile epilepsy, inherited a known pathogenic c.4840A>G variant from his father with similar symptoms. Cases 2 to 4 had presented with intermediate epilepsy. Among these, case 2 has harbored a de novo c.3967G>A variant which was rated as pathogenic (PS1+PS2+PM1+PM2_Supporting+PP3) based on the guidelines from the American College of Medical Genetics and Genomics. Cases 3 and 4 were found to respectively harbor a de novo c.415A>T and a c.4697C>T variant, which were both rated as likely pathogenic (PS2+PM1+PM2_Supporting+PP3). Case 5, who had early-onset infantile epileptic encephalopathy transformed into Lennox Gastaut-like syndrome, has harbored a de novo c.5615G>A variant, which was known to be pathogenic. The children had their age of onset ranging from 2 to 14 months, and all had focal seizures and generalized tonic clonic seizures. Four children (cases 1, 2, 3 and 5) had cluster seizures, four (cases 1 to 4) had become seizure-free after single or dual treatment and showed normal growth and development, whilst case 5 was drug-resistant and showed severe developmental retardation. The five children had new features such as cluster seizures, occasional benign seizures in adulthood, and intermediate epilepsy which are prone to relapse after discontinuation of medication, which may be attributed to the pathogenic variants of the SCN8A gene.

Early-Onset Dystonia and Visual Impairment Preceding Epileptic Encephalopathy Associated with PIGA Gene Mutation.

The association between dystonia and early-onset epileptic encephalopathy (EOEE) may have a genetic basis. Phosphatidylinositol glycan biosynthesis class A protein (PIGA) germline mutations have been described in the last decade and associated with refractory EOEEs. Dysmorphisms and visceral abnormalities have also been reported. Here, we present the case of a now 8-month-old child who was evaluated for dystonia, visual impairment, and developmental delay at 2 months of age, followed by refractory focal seizures when he was 4 months old. The remaining examination was normal, besides an accelerated linear growth. His brain magnetic resonance and an extensive metabolic investigation failed to show any abnormalities. At 7 months of age, the exome sequencing found a hemizygous PIGA pathogenic variant-c.1352T > C (p.(Ile451Thr). Seizures improved after the association of carbamazepine with levetiracetam and the beginning of the ketogenic diet. To our knowledge, this is the first time the phenotype associated with this specific mutation is described. Our patient had the singularity of manifesting with remarkable dystonia, over 2 months before the onset of seizures. We also point to the utility of the gene sequencing approach in the diagnosis of patients with dystonia and EOEEs, since identification of the genetic cause may help in patient's management and families' empowerment.

Type 1 early infantile epileptic encephalopathy: A case report and literature review.

Variants in the Aristaless-related homeobox (ARX) gene lead to a variety of phenotypes, with intellectual disability being a steady feature. Other features can include severe epilepsy, spasticity, movement disorders, hydranencephaly, and ambiguous genitalia in males. X-linked Ohtahara syndrome or Type 1 early infantile epileptic encephalopathy (EIEE1) is a severe early-onset epileptic encephalopathy with arrested psychomotor development caused by hemizygous mutations in the ARX gene, which encodes a transcription factor in fundamental brain developmental processes. We presented a case report of a 2-year-old boy who exhibited symptoms such as microcephaly, seizures, and severe multifocal epileptic abnormalities, and genetic techniques such as autozygosity mapping, Sanger sequencing, and whole-exome sequencing. We confirmed that the patient had the NM_139058.3:c.84C>A; p.(Cys28Ter) mutation in the ARX gene. The patient with EIEE1 had physical symptoms and hypsarrhythmia on electroencephalogram. Genetic testing identified a causative mutation in the ARX gene, emphasizing the role of genetic testing in EIEE diagnosis.

Adult-onset combined oxidative phosphorylation deficiency type 14 manifests as epileptic status: a new phenotype and literature review

BackgroundCombined oxidative phosphorylation deficiency (COXPD) is a severe disorder with early onset and autosomal recessive inheritance, and has been divided into 51 types (COXPD1–COXPD51). COXPD14 is caused by a mutation in the FARS2 gene, which encodes mitochondrial phenylalanyl-tRNA synthetase (mt-PheRS), an enzyme that transfers phenylalanine to its cognate tRNA in mitochondria. Since the first case was reported in 2012, an increasing number of FARS2 variations have been subsequently identified, which present three main phenotypic manifestations: early onset epileptic encephalopathy, hereditary spastic paraplegia, and juvenile-onset epilepsy. To our knowledge, no adult cases have been reported in the literature.MethodsWe report in detail a case of genetically confirmed COXPD14 and review the relevant literature.ResultsApproximately 58 subjects with disease-causing variants of FARS2 have been reported, including 31 cases of early onset epileptic encephalopathy, 16 cases of hereditary spastic paraplegia, 3 cases of juvenile-onset epilepsy, and 8 cases of unknown phenotype. We report a case of autosomal recessive COXPD14 in an adult with status epilepticus as the only manifestation with a good prognosis, which is different from that in neonatal or infant patients reported in the literature. c.467C > T (p.T156M) has been previously reported, while c.119_120del (p.E40Vfs*87) is novel, and, both mutations are pathogenic.ConclusionsThis case of autosomal recessive COXPD14 in an adult only presented as status epilepticus, which is different from the patients reported previously. Our study expands the mutation spectrum of FARS2, and we tended to define the phenotypes based on the clinical manifestation rather than the age of onset.

Spectrum of NMDA Receptor Variants in Neurodevelopmental Disorders and Epilepsy.

N-methyl-D-aspartate receptors (NMDAR) are ligand-gated ion channels mediating excitatory neurotransmission and are important for normal brain development, cognitive abilities, and motor functions. Pathogenic variants in the Glutamate receptor Ionotropic N-methyl-D-aspartate (GRIN) genes (GRIN1, GRIN2A-D) encoding NMDAR subunits have been associated with a wide spectrum of neurodevelopmental disorders and epilepsies ranging from treatable focal epilepsies to devastating early-onset developmental and epileptic encephalopathies. Genetic variants in NMDA receptor genes can cause a range of complex alterations to receptor properties resulting in various degrees of loss-of-function, gain-of-function, or mixtures thereof. Understanding how genetic variants affect the function of the receptors, therefore, represents an important first step in the ongoing development towards targeted therapies. Currently, targeted treatment options for GRIN-related diseases are limited. However, treatment with memantine has been reported to significantly reduce seizure frequency in a few individuals with developmental and epileptic encephalopathies harboring de novo gain-of-function GRIN2A missense variants, and supplementary treatment with L-serine has been associated with improved motor and cognitive performance as well as reduced seizure frequency in patients with GRIN2B loss-of-function missense variants as well as GRIN2A and GRIN2B null variants.

Neurodevelopmental deficits and cell-type-specific transcriptomic perturbations in a mouse model of HNRNPU haploinsufficiency.

Heterozygous de novo loss-of-function mutations in the gene expression regulator HNRNPU cause an early-onset developmental and epileptic encephalopathy. To gain insight into pathological mechanisms and lay the potential groundwork for developing targeted therapies, we characterized the neurophysiologic and cell-type-specific transcriptomic consequences of a mouse model of HNRNPU haploinsufficiency. Heterozygous mutants demonstrated global developmental delay, impaired ultrasonic vocalizations, cognitive dysfunction and increased seizure susceptibility, thus modeling aspects of the human disease. Single-cell RNA-sequencing of hippocampal and neocortical cells revealed widespread, yet modest, dysregulation of gene expression across mutant neuronal subtypes. We observed an increased burden of differentially-expressed genes in mutant excitatory neurons of the subiculum-a region of the hippocampus implicated in temporal lobe epilepsy. Evaluation of transcriptomic signature reversal as a therapeutic strategy highlights the potential importance of generating cell-type-specific signatures. Overall, this work provides insight into HNRNPU-mediated disease mechanisms and provides a framework for using single-cell RNA-sequencing to study transcriptional regulators implicated in disease.

First report of Tunisian patients with CDKL5-related encephalopathy.

Mutations in the cyclin-dependent kinase-like 5 gene (CDKL5) are associated with a wide spectrum of clinical presentations. Early-onset epileptic encephalopathy (EOEE) is the most recognized phenotype. Here we describe phenotypic features in 8 Tunisian patients with CDKL5-related encephalopathy. We included all cases with clinical features consistent with CDKL5-related encephalopathy: infantile epileptic spasm, acquired microcephaly, movement disorders and visual impairment. We collected data about seizure types, electroencephalogram, magnetic resonance imaging and metabolic analysis. The diagnosis of CDKL5 mutation was made thanks to Sanger sequencing with an ABI PRISM 3100-Avant automated DNA sequencer using a Big Dye Terminator Cycle Sequencing Reaction Kit v1.1. and Next Generation Sequencing (NGS) since the development of a gene panel responsible for DEE within the framework of "Strengthening the Sfax University Expertise for diagnosis and management of epileptic encephalopathies". We collected 4 boys and 4 girls aged meanly 6-years-old with confirmed mutation on CDKL5 gene. Overall, we identified 5 de novo CDKL5 mutations including three Frameshift mutations; one missense mutation and a splicing variant. The mean age at first seizure onset was 4 months. The first seizure type was infantile epileptic spasm (4/8) followed by tonic (2/8) and myoclonic seizures (2/8). Out of 8 cases, 4 exhibited two stages epileptic course while epilepsy in 3 other patients progressed on three stages. Regarding development, most cases (6/8) had psychomotor retardation from the start whilst the two others showed psychomotor regression with the onset of seizures. Additional clinical features included visual impairment (7/8), tone abnormalities (7/8), stereotypies (7/8) and acquired microcephaly (6/8). Our present report delineates an unusual phenotype of CDKL5-related encephalopathy with male gender predominance and delayed onset epilepsy. It interestingly described new phenotypic features and uncommon benign developmental profiles in boys, different patterns of CDKL5-epilepsy, neuroimaging findings and CDKL5 mutational spectru.

Delineating the phenotype of PNPLA8-related mitochondriopathies.

Pathogenic variants in PNPLA8 have been described either with congenital onset displaying congenital microcephaly, early onset epileptic encephalopathy and early lethality or childhood neurodegeneration with progressive microcephaly. Moreover, a phenotype comprising adulthood onset cerebellar ataxia and peripheral neuropathy was also reported. To our knowledge, only six patients with biallelic variants in PNPLA8 have been reported so far. Here, we report the clinical and molecular characterizations of three additional patients in whom exome sequencing identified a loss of function variant (c.1231C>T, p.Arg411Ter) in Family I and a missense variant (c.1559T>A, p.Val520Asp) in Family II in PNPLA8. Patient 1 presented with the congenital form of the disease while Patients 2 and 3 showed progressive microcephaly, infantile onset seizures, progressive cortical atrophy, white matter loss, bilateral degeneration of basal ganglia, and cystic encephalomalacia. Therefore, our results add the infantile onset as a new distinct phenotype of the disease and suggest that the site of the variant rather than its type is strongly correlated with the disease onset. In addition, these conditions demonstrate some overlapping features representing a spectrum with clinical features always aligning with different age of onset.

Comment: Amenable Treatable Severe Pediatric Epilepsies

Phillip L. Pearl Seminars in Pediatric Neurology Volume 23, Issue 2, May 2016, Pages 158-166 Vitamin-dependent epilepsies and multiple metabolic epilepsies are amenable to treatment that markedly improves the disease course. Knowledge of these amenably treatable severe pediatric epilepsies allows for early identification, testing, and treatment. These disorders present with various phenotypes, including early onset epileptic encephalopathy (refractory neonatal seizures, early myoclonic encephalopathy, and early infantile epileptic encephalop athy), infantile spasms, or mixed generalized seizure types in infancy, childhood, or even adolescence and adulthood. The disorders are presented as vitamin responsive epilepsies such as pyridoxine, pyridoxal-5-phosphate, folinic acid, and biotin; transportopathies like GLUT-1, cerebral folate deficiency, and biotin thiamine responsive disorder; amino and organic acidopathies including serine synthesis defects, creatine synthesis disorders, molybdenum cofactor deficiency, and cobalamin deficiencies; mitochondrial disorders; urea cycle disorders; neurotransmitter defects; and disorders of glucose homeostasis. In each case, targeted intervention directed toward the underlying metabolic pathophysiology affords for the opportunity to significantly effect the outcome and prognosis of an otherwise severe pediatric epilepsy.

Melkersson-Rosenthal Syndrome and Migraine: A New Phenotype Associated with SCN1A Variants?

Peripheral facial palsy rarely occurs as part of Melkersson-Rosenthal syndrome (MRS), which is characterized by the classical triad of tongue cheilitis, recurrent episodes of orofacial swelling, and palsy. MRS is a disorder with variable expressivity and clinical as well as genetic heterogeneity; however, the causative gene remains to be identified. Migraine is a common neurological disorder, presenting with or without aura, which may be associated with neurological symptoms. The classical example of monogenic migraine is familial hemiplegic migraine (FHM), which has phenotypic variability in carriers of variants in the same gene or even carriers of the same variant. We present a family in which two sisters displayed recurrent migraines, one of which presented recurrent facial palsy and had clinical diagnosis of MRS. We performed WES and Sanger sequencing for segregation analysis in the available family members. We identified a c.3521C>G missense heterozygous variant in SCN1A carried only by the affected sister. Variants in the SCN1A gene can cause a spectrum of early-onset epileptic encephalopathies, in addition to FHM; therefore, our finding reasonably explains the proband phenotype, in which the main symptom was recurrent facial palsy. This report also adds knowledge to the clinical spectrum of SCN1A alterations and suggests a potential overlap between MRS and FHM.

Stretch-activated ion channel TMEM63B associates with developmental and epileptic encephalopathies and progressive neurodegeneration

By converting physical forces into electrical signals or triggering intracellular cascades, stretch-activated ion channels allow the cell to respond to osmotic and mechanical stress. Knowledge of the pathophysiological mechanisms underlying associations of stretch-activated ion channels with human disease is limited. Here, we describe 17 unrelated individuals with severe early-onset developmental and epileptic encephalopathy (DEE), intellectual disability, and severe motor and cortical visual impairment associated with progressive neurodegenerative brain changes carrying ten distinct heterozygous variants of TMEM63B, encoding for a highly conserved stretch-activated ion channel. The variants occurred de novo in 16/17 individuals for whom parental DNA was available and either missense, including the recurrent p.Val44Met in 7/17 individuals, or in-frame, all affecting conserved residues located in transmembrane regions of the protein. In 12 individuals, hematological abnormalities co-occurred, such as macrocytosis and hemolysis, requiring blood transfusions in some. We modeled six variants (p.Val44Met, p.Arg433His, p.Thr481Asn, p.Gly580Ser, p.Arg660Thr, and p.Phe697Leu), each affecting a distinct transmembrane domain of the channel, in transfected Neuro2a cells and demonstrated inward leak cation currents across the mutated channel even in isotonic conditions, while the response to hypo-osmotic challenge was impaired, as were the Ca2+ transients generated under hypo-osmotic stimulation. Ectopic expression of the p.Val44Met and p.Gly580Cys variants in Drosophila resulted in early death. TMEM63B-associated DEE represents a recognizable clinicopathological entity in which altered cation conductivity results in a severe neurological phenotype with progressive brain damage and early-onset epilepsy associated with hematological abnormalities in most individuals.

Neonatal Status Epilepticus Secondary to Nonketotic Hyperglycinemia: Efficacy of Low-Dose Dextromethorphan

AbstractNonketotic hyperglycinemia is a severe form of early onset epileptic encephalopathy caused by disturbances in the glycine cleavage system, leading to neurological damage attributed to overstimulation of the N-methyl-D-aspartate receptor. Although there are no interventions known to be effective in altering the natural history of nonketotic hyperglycinemia, it is very important that the clinician recognizes this disease and initiates early evaluation and treatment to attain the best possible outcome. Here we present a newborn diagnosed with a severe form of nonketotic hyperglycinemia with frequent myoclonic seizures, which were resistant to phenobarbital, levetiracetam, ketogenic diet, sodium benzoate, and perampanel. Dextromethorphan reduced epileptic myoclonic jerks and improved the background activity on the electroencephalogram.

0041 Neuronal circuits convergently disrupted in the genetic basis of sleep phenotypes and rare neurodevelopmental syndromes

Abstract Introduction Sleep-related phenotypes have been frequently reported in early on-set epileptic encephalopathies (EE) and in developmental delay (DD) syndromes, in particular in syndromes related to autism spectrum disorder (ASD). Yet the convergent pathogenetic mechanisms between these comorbidities are largely unknown. Methods We first performed a gene enrichment study that identified shared risk genes among rare EE/neurodevelopmental disorders (NDD), rare DD genetic syndromes and sleep disturbances. We then determined cellular and molecular pathways enriched among genes shared between sleep phenotypes and those two early onset mental illnesses, aiming to identify genetic disparities and commonalities among these phenotypic groups. Results The sleep gene set was observed as significantly overlapped with the two gene lists associated to rare genetic syndromes (i.e. EE/NDD and DD gene sets), suggesting shared genetic contribution. Similarities across significantly enriched pathways between the two intersect lists comprehended mostly synapse-related pathways, such as retrograde endocannabinoid signaling, serotonergic and GABAergic synapse. Network analysis indicates EE/NDD vs sleep specific clusters and DD vs sleep specific clusters related to synaptic and transcriptional regulation, respectively. Longstanding functional patterns previously described in EE and NDD genetic architecture were recaptured after dissecting the overlap between the genes associated to those developmental phenotypes and sleep disturbances, suggesting that during neurodevelopment different molecular and functional mechanisms are related to alterations on circadian rhythm. Conclusion The overlapping gene set and biological pathways highlighted by this study may serve as a primer for new functional investigations of shared molecular mechanisms between sleep disturbances and rare developmental syndromes, with or without epilepsy. Support (if any) Our studies are supported by Associação Fundo de Incentivo à Pesquisa (AFIP). S.T. and M.L.A. received CNPq fellowships.

Genetic basis of sleep phenotypes and rare neurodevelopmental syndromes reveal shared molecular pathways.

Sleep-related phenotypes have been frequently reported in early on-set epileptic encephalopathies and in developmental delay syndromes, in particular in syndromes related to autism spectrum disorder. Yet the convergent pathogenetic mechanisms between these comorbidities are largely unknown. We first performed a gene enrichment study that identified shared risk genes among rare epileptic encephalopathies/neurodevelopmental disorders, rare developmental delay genetic syndromes and sleep disturbances. We then determined cellular and molecular pathways enriched among genes shared between sleep phenotypes and those two early onset mental illnesses, aiming to identify genetic disparities and commonalities among these phenotypic groups. The sleep gene set was observed as significantly overlapped with the two gene lists associated to rare genetic syndromes (i.e., epileptic encephalopathies/neurodevelopmental disorders and developmental delay gene sets), suggesting shared genetic contribution. Similarities across significantly enriched pathways between the two intersect lists comprehended mostly synapse-related pathways, such as retrograde endocannabinoid signaling, serotonergic, and GABAergic synapse. Network analysis indicates epileptic encephalopathies/neurodevelopmental disorders versus sleep-specific clusters and developmental delay versus sleep-specific clusters related to synaptic and transcriptional regulation, respectively. Longstanding functional patterns previously described in epileptic encephalopathies and neurodevelopmental disorders genetic architecture were recaptured after dissecting the overlap between the genes associated to those developmental phenotypes and sleep disturbances, suggesting that during neurodevelopment different molecular and functional mechanisms are related to alterations on circadian rhythm. The overlapping gene set and biological pathways highlighted by this study may serve as a primer for new functional investigations of shared molecular mechanisms between sleep disturbances and rare developmental syndromes.

Cohen syndrome and early-onset epileptic encephalopathy in male triplets: two disease-causing mutations in VPS13B and NAPB

Cohen syndrome (CS) is a rare multisystem autosomal recessive disorder associated with mutations in VPS13B (vacuolar protein sorting homolog 13B). The NAPB-related neurodevelopmental disorder is characterized mainly by early-onset epileptic encephalopathy (EOEE) and is associated with mutations in NAPB that encodes for SNAP-beta (soluble NSF attachment protein beta). Here we describe male triplets, clinically presenting with the phenotype of subtle but distinctive facial features, intellectual disability, increased body weight, neonatal EOEE, and prominently variable abnormal behaviors of autism and sexual arousal. The EEG showed multifocal epilepsy, while the brain MRI showed no abnormalities. Diagnostic exome sequencing (ES), the applied next-generation sequencing approach, revealed the interesting finding of two novel homozygous variants in two genes: VPS13B missense variant (c.8516G > A) and NAPB splice-site loss (c.354 + 2 T > G). Sanger sequencing verified the segregation of the two recessive gene variants with the phenotype in family members. The prediction algorithms support the pathogenicity of these variants. Homozygosity mapping of ES data of this consanguineous family revealed multiple chromosomal regions of homozygosity stretches with the residing of VPS13B (chr8: 100830758G > A) and NAPB (Chr20: 23,375,774 A > C) variants within the largest homozygous blocks further supporting the disease-genes causal role. Interestingly, the functions of the two proteins; VPS13B, a transmembrane protein involved in intracellular protein transport, and SNAP-beta involved in neurotransmitters release at the neuronal synaptic complexes, have been associated with Golgi-mediated vesicular trafficking. Our ES findings provide new insights into the pathologic mechanism underlying the expansion of the neurodevelopmental spectrum in CS and further highlight the importance of Golgi and Golgi-membrane-related proteins in the development of neurodevelopmental syndromes associated with early-onset non-channelopathy epilepsy. To our knowledge, this is the first report documenting multifocal EOEE in CS patients with the association of a pathogenic NAPB variant.