NUP85 as a Neurodevelopmental Gene: From Podocyte to Neuron.

Pathogenic gene variants encoding nuclear pore complex (NPC) proteins were previously implicated in the pathogenesis of steroid-resistant nephrotic syndrome (SRNS). The NUP85 gene, encoding nucleoporin, is related to a very rare form of SRNS with limited genotype-phenotype information. We identified an Italian boy affected with an SRNS associated with severe neurodevelopmental impairment characterized by microcephaly, axial hypotonia, lack of achievement of motor milestones, and refractory seizures with an associated hypsarrhythmic pattern on electroencephalography. Brain magnetic resonance imaging (MRI) showed hypoplasia of the corpus callosum and a simplified gyration of the cerebral cortex. Since the age of 3 years, the boy was followed up at our Pediatric Nephrology Department for an SRNS, with a focal segmental glomerulosclerosis at renal biopsy. The boy died 32 months after SRNS onset, and a Whole-Exome Sequencing analysis revealed a novel compound heterozygous variant in NUP85 (NM_024844.5): 611T>A (p.Val204Glu), c.1904T>G (p.Leu635Arg), inherited from the father and mother, respectively. We delineated the clinical phenotypes of NUP85-related disorders, reviewed the affected individuals so far reported in the literature, and overall expanded both the phenotypic and the molecular spectrum associated with this ultra-rare genetic condition. Our study suggests a potential occurrence of severe neurological phenotypes as part of the NUP85-related clinical spectrum and highlights an important involvement of nucleoporin in brain developmental processes and neurological function.

The Cardiofaciocutaneous Syndrome: From Genetics to Prognostic-Therapeutic Implications.

Cardiofaciocutaneous (CFC) syndrome is one of the rarest RASopathies characterized by multiple congenital ectodermal, cardiac and craniofacial abnormalities with a mild to severe ocular, gastrointestinal and neurological involvement. It is an autosomal dominant syndrome, with complete penetrance, caused by heterozygous pathogenic variants in the genes BRAF, MAP2K1/MEK1, MAP2K2/MEK2, KRAS or, rarely, YWHAZ, all part of the RAS-MAPK pathway. This pathway is a signal transduction cascade that plays a crucial role in normal cellular processes such as cell growth, proliferation, differentiation, survival, metabolism and migration. CFC syndrome overlaps with Noonan syndrome, Costello syndrome, neurofibromatosis type 1 and Legius syndrome, therefore making the diagnosis challenging. Neurological involvement in CFC is more severe than in other RASopathies. Phenotypic variability in CFC patients is related to the specific gene affected, without a recognized genotype-phenotype correlation for distinct pathogenic variants. Currently, there is no specific treatment for CFC syndrome. Encouraging zebrafish model system studies suggested that, in the future, MEK inhibitors could be a suitable treatment of progressive phenotypes of CFC in children. A multidisciplinary care is necessary for appropriate medical management.

Familial hemiplegic migraine in pediatric patients: A genetic, clinical, and follow-up study.

OBJECTIVE: The aim of this study was to describe a cohort of pediatric patients with genetically confirmed familial hemiplegic migraine (FHM). The knowledge of genotype-phenotype correlations may suggest prognostic factors associated with severe phenotypes. BACKGROUND: Hemiplegic migraine is a rare disease and data concerning the pediatric population are even more rare as they are often extrapolated from mixed cohorts. METHODS: We selected patients who met International Classification of Headache Disorders, third edition criteria for FHM, who had a molecular diagnosis, and whose first attack occurred under the age of 18 years. RESULTS: We enrolled nine patients (seven males and two females) first referred to our three centers. Three of the nine (33%) patients had calcium voltage-gated channel subunit alpha1 A (CACNA1A) mutations, five (55%) had ATPase Na+/K+ transporting subunit alpha 2 (ATP1A2) mutations, and one had both genetic mutations. The patients experienced at least one aura feature other than hemiplegia during the first attack. The mean (SD) duration of HM attacks in the sample was 11.3 (17.1) h; 3.8 (6.1) h in the ATP1A2 group, and 24.3 (23.5) h in the CACNA1A group. The mean (SD, range) duration of follow-up was 7.4 (2.2, 3-10) years. During the first year from the disorder's onset, only four patients had additional attacks. Over the course of follow-up, the attack frequency overall was 0.4 attacks/year without a difference between the two groups (CACNA1A and ATP1A2). CONCLUSION: The study data show that most of our patients with early-onset FHM experienced infrequent and non-severe attacks, which improved over time. Furthermore, the clinical course revealed neither the appearance of novel neurological disorders or a deterioration of basic neurological or cognitive functioning.

KCNT2-Related Disorders: Phenotypes, Functional, and Pharmacological Properties.

OBJECTIVE: Pathogenic variants in KCNT2 are rare causes of developmental epileptic encephalopathy (DEE). We herein describe the phenotypic and genetic features of patients with KCNT2-related DEE, and the in vitro functional and pharmacological properties of KCNT2 channels carrying 14 novel or previously untested variants. METHODS: Twenty-five patients harboring KCNT2 variants were investigated: 12 were identified through an international collaborative network, 13 were retrieved from the literature. Clinical data were collected and included in a standardized phenotyping sheet. Novel variants were detected using exome sequencing and classified using ACMG criteria. Functional and pharmacological studies were performed by whole-cell electrophysiology in HEK-293 and SH-SY5Y cells. RESULTS: The phenotypic spectrum encompassed: (a) intellectual disability/developmental delay (21/22 individuals with available information), ranging from mild to severe/profound; (b) epilepsy (15/25); (c) neurological impairment, with altered muscle tone (14/22); (d) dysmorphisms (13/20). Nineteen pathogenic KCNT2 variants were found (9 new, 10 reported previously): 16 missense, 1 in-frame deletion of a single amino acid, 1 nonsense, and 1 frameshift. Among tested variants, 8 showed gain-of-function (GoF), and 6 loss-of-function (LoF) features when expressed heterologously in vitro. Quinidine and fluoxetine blocked all GoF variants, whereas loxapine and riluzole activated some LoF variants while blocking others. INTERPRETATION: We expanded the phenotypic and genotypic spectrum of KCNT2-related disorders, highlighting novel genotype-phenotype associations. Pathogenic KCNT2 variants cause GoF or LoF in vitro phenotypes, and each shows a unique pharmacological profile, suggesting the need for in vitro functional and pharmacological investigation to enable targeted therapies based on the molecular phenotype. ANN NEUROL 2023;94:332-349.

A homozygous MED11 C-terminal variant causes a lethal neurodegenerative disease.

PURPOSE: The mediator (MED) multisubunit-complex modulates the activity of the transcriptional machinery, and genetic defects in different MED subunits (17, 20, 27) have been implicated in neurologic diseases. In this study, we identified a recurrent homozygous variant in MED11 (c.325C>T; p.Arg109Ter) in 7 affected individuals from 5 unrelated families. METHODS: To investigate the genetic cause of the disease, exome or genome sequencing were performed in 5 unrelated families identified via different research networks and Matchmaker Exchange. Deep clinical and brain imaging evaluations were performed by clinical pediatric neurologists and neuroradiologists. The functional effect of the candidate variant on both MED11 RNA and protein was assessed using reverse transcriptase polymerase chain reaction and western blotting using fibroblast cell lines derived from 1 affected individual and controls and through computational approaches. Knockouts in zebrafish were generated using clustered regularly interspaced short palindromic repeats/Cas9. RESULTS: The disease was characterized by microcephaly, profound neurodevelopmental impairment, exaggerated startle response, myoclonic seizures, progressive widespread neurodegeneration, and premature death. Functional studies on patient-derived fibroblasts did not show a loss of protein function but rather disruption of the C-terminal of MED11, likely impairing binding to other MED subunits. A zebrafish knockout model recapitulates key clinical phenotypes. CONCLUSION: Loss of the C-terminal of MED subunit 11 may affect its binding efficiency to other MED subunits, thus implicating the MED-complex stability in brain development and neurodegeneration.

A complex epileptic and dysmorphic phenotype associated with a novel frameshift KDM5B variant and deletion of SCN gene cluster.

The histone demethylase family plays a key role in chromatin structure and gene regulation during development. Mutations in the genes encoding the lysine demethylase 5 (KDM5) were reported in individuals with many diseases, including neurodevelopmental disorders such as intellectual disability. Recently, KDM5B has been identified as a gene regulator causative of recessive neurodevelopmental disorders. Although numerous variants in this gene have been identified, genotype / phenotype correlation remains variable. We report a patient with two de novo mutations, a frameshift KDM5B variant and a 2q deletion of 8.2 Mb, associated with a phenotype including facial and finger dysmorphisms, severe intellectual and motor disorders, and a rare epileptic syndrome identified as epilepsy of infancy with migrating focal seizures. Comparison with previous reports suggests that the KDM5B variant could play a potential role on dysmorphic features; conversely, the epileptic disorder is mainly caused by the haploinsufficiency of the Nav1 mediated gabaergic inhibition.

Commonalities and distinctions between two neurodevelopmental disorder subtypes associated with SCN2A and SCN8A variants and literature review.

This study was aimed to analyze the commonalities and distinctions of voltage-gated sodium channels, Nav1.2, Nav1.6, in neurodevelopmental disorders. An observational study was performed including two patients with neurodevelopmental disorders. The demographic, electroclinical, genetic, and neuropsychological characteristics were analyzed and compared with each other and then with the subjects carrying the same genetic variants reported in the literature. The clinical features of one of them argued for autism spectrum disorder and developmental delay, the other for intellectual disability, diagnoses confirmed by the neuropsychological assessment. The first patient was a carrier of SCN2A (p.R379H) variant while the second was carrier of SCN8A (p.E936K) variant, both involving the pore loop of the two channels. The results of this study suggest that the neurodevelopmental disorders without overt epilepsy of both patients can be the consequences of loss of function of Nav1.2/Nav1.6 channels. Notably, the SCN2A variant, with an earlier expression timing in brain development, resulted in a more severe phenotype as autism spectrum disorder and developmental delay, while the SCN8A variant, with a later expression timing, resulted in a less severe phenotype as intellectual disability.

De novo GRIN2A variants associated with epilepsy and autism and literature review.

N-methyl-D-aspartate receptors (NMDAR) are di- or tri-heterotetrameric ligand-gated ion channels composed of two obligate glycine-binding GluN1 subunits and two glutamate-binding GluN2 or GluN3 subunits, encoded by GRIN1, GRIN2A-D, and GRIN3A-B receptor genes respectively. Each NMDA receptor subtype has different temporal and spatial expression patterns in the brain and varies in the cell types and subcellular localization resulting in different functions. They play a crucial role in mediating the excitatory neurotransmission, but are also involved in neuronal development and synaptic plasticity, essential for learning, memory, and high cognitive functions. Among genes coding NMDAR subunits, GRIN2B is predominantly associated with neurodevelopmental disorders such as intellectual disability, developmental delay, autism, attention-deficit/hyperactivity disorder and, further, schizophrenia, Alzheimer's disease. The GRIN2A seems to be predominantly associated with a more definite phenotype including an epileptic spectrum ranging from Landau-Kleffner syndrome to benign childhood epilepsy with centrotemporal spikes, speech or language impairment, intellectual disability/developmental delay often in comorbidity. On the contrary, the occurrence of autism spectrum disorders, unlike GRIN2B-associated disorders, is questionable. To contribute to elucidate the latter issue and to better define the genotype/phenotype correlation, we report the clinical and neuropsychological profile of two patients featuring autism disorder, intellectual disability, language impairment, and focal epilepsy, associated with previously unreported heterozygous de novo GRIN2A pathogenic variants. We hypothesize that the unusual phenotype may be the result of interactions of tri-heterotetrameric 2GluN1/GluN2A-D/GluN3A-B subunits with mutated GluN2A subunit and/or the dysfunction may be influenced by other unknown modifier genes and/or environmental factors.

Recurrent missense variant in the nuclear export signal of FMR1 associated with FXS-like phenotype including intellectual disability, ASD, facial abnormalities.

Fragile X syndrome (FXS; MIM 300624) is an X-linked genetic disorder characterized by physical abnormalities associated with intellectual disability and a wide spectrum of neurological and psychiatric impairments. FXS occurs more frequently in males, 1 in 5000 males and 1 in 8000 females accounting for 1-2% of overall intellectual disability (ID). In more than 99% of patients, FXS results from expansions of a CGG triplet repeat (>200 in male) of the FMR1 gene. In the last years an increasing number, albeit still limited, of FXS subjects carrying FMR1 mutations including deletions, splicing errors, missense, and nonsense variants was reported. Nevertheless, the studies concerning the functional consequences of mutations in the FMR1 gene are rare so far and, therefore, we do not have sufficient knowledge regarding the genotype/phenotype correlation. We report a child carrying a hemizygous missense FMR1 (NM_002024.5:c.1325G > A p.Arg442Gln) variant, maternally inherited, associated with facial abnormalities, developmental delay, and social and communication deficits assessed with formal neuropsychological tests. The study contributes to highlighting the clinical differences between the CGG triplet repeat dependent phenotype and FMR1variant dependent phenotype and it also confirms the pathogenicity of the variant being reported for the second time in the literature.

Resolution of enuresis with aripiprazole in children with psychiatric disorders: two case reports.

BACKGROUND: Aripiprazole is a third-generation atypical antipsychotic drug that acts as a stabilizer of the dopaminergic and serotonergic system. As partial agonist of the dopamine (D2) and serotonin (5-HT1A) receptors, it appears to be effective in reducing mania in patients with bipolar disorder, tics in Tourette Syndrome, aggression in schizophrenia and autism spectrum disorder. Enuresis has been reported among its side effects. Only a few studies, with conflicting results, have investigated the relationship between aripiprazole and enuresis. CASE PRESENTATION: We report the disappearance of enuresis in a Caucasian girl with intellectual disability and oppositional defiant disorder and in a Caucasian boy with intellectual disability and early-onset psychosis, both following initiation of treatment with aripiprazole. CONCLUSION: The aim of this study was to contribute to the literature on the use of aripripazole in subjects with enuresis. Our findings lead us to suggest that aripiprazole is less burdened with side effects, including bedwetting, than other antipsychotic drugs.

A paradigmatic autistic phenotype associated with loss of PCDH11Y and NLGN4Y genes.

BACKGROUND: Most studies relative to Y chromosome abnormalities are focused on the sexual developmental disorders. Recently, a few studies suggest that some genes located on Y chromosome may be related to different neurodevelopment disorders. CASE PRESENTATION: We report a child with sexual developmental disorder associated with a peculiar phenotype characterized by severe language impairment and autistic behaviour associated with a mosaicism [45,X(11)/46,XY(89)] and a partial deletion of the short and long arm of Y chromosome (del Yp11.31q11.23) that also involves the loss of both PCDH11Y and NLGN4Y genes. To our knowledge no study has ever reported the occurrence of the lack of both PCDH11Y and NLGN4Y located in the Y chromosome in the same patient. CONCLUSIONS: We hypothesized a functional complementary role of PCDH11Y and NLGN4Y within formation/maturation of the cerebral cortex. The impairment of early language development may be mainly related to the lack of PCDH11Y that underlies the early language network development and the later appearance of the autistic behaviour may be mainly related to deficit of inhibitory glicinergic neurotransmission NLGN4Y-linked.

Broad neurodevelopmental features and cortical anomalies associated with a novel de novo KMT2A variant in Wiedemann-Steiner syndrome.

Wiedemann-Steiner syndrome (WDSTS) is a rare genetic disorder including developmental delay/intellectual disability (DD/ID), hypertrichosis cubiti, short stature, and distinctive facial features, caused by mutation in KMT2A gene, which encodes a histone methyltransferase (H3K4) that regulates chromatin-mediated transcription. Different neurodevelopmental phenotypes have been described within the WDSTS spectrum, including a peculiar Autism Spectrum Disorder (ASDs) subtype in some affected individuals. Here, we report a 9-year-old Caucasian male found by next-generation panel sequencing to carry a novel heterozygous de novo KMT2A frameshift variant (NM_001197104.2:c.4433delG; p. Arg1478LeufsTer108). This boy presented a WDSTS phenotype associated with broad neurodevelopmental features, including an unusual speech difficulty (i.e., palilalia), and brain imaging studies revealed an array of cortical anomalies (e.g., frontal simplified gyration, focal frontal cortical dysplasia). These clinical and radiological observations expand the known WDSTS-related neurodevelopmental phenotypes and further strengthen the important role of KMT2A in brain function and cortical development.

Benign familial infantile epilepsy associated with KCNQ3 mutation: a rare occurrence or an underestimated event?

Benign familial infantile epilepsy (BFIE) is the most genetically heterogeneous phenotype among early-onset familial infantile epilepsies. It has an autosomal dominant inheritance pattern with incomplete penetrance. Although PRRT2 is the most mutated gene detected in families with BFIE, other mutations in KCNQ2, SCN2A, and GABRA6 genes have also been described. To date, KCNQ3 mutations have been detected in only four patients with BFIE. Here, we describe the clinical pattern and course of an additional individual with BFIE associated with a novel missense heterozygous KCNQ3 c.1850G>C variant inherited by his unaffected father. The incidence of KCNQ3 mutations among BFIE patients is reported to be low in the literature, however, whether this is underestimated is unclear as not all current epilepsy gene panels include KCNQ3.

Two distinct phenotypes, hemiplegic migraine and episodic Ataxia type 2, caused by a novel common CACNA1A variant.

BACKGROUND: To investigate the genetic and environmental factors responsible for phenotype variability in a family carrying a novel CACNA1A missense mutation. Mutations in the CACNA1A gene were identified as responsible for at least three autosomal dominant disorders: FHM1 (Familial Hemiplegic Migraine), EA2 (Episodic Ataxia type 2), and SCA6 (Spinocerebellar Ataxia type 6). Overlapping clinical features within individuals of some families sharing the same CACNA1A mutation are not infrequent. Conversely, reports with distinct phenotypes within the same family associated with a common CACNA1A mutation are very rare. CASE PRESENTATION: A clinical, molecular, neuroradiological, neuropsychological, and neurophysiological study was carried out in proband and his carrier mother. The new heterozygous missense variant c.4262G > A (p.Arg1421Gln) in the CACNA1A gene was detected in the two affected family members. The proband showed a complex clinical presentation characterized by developmental delay, poor motor coordination, hemiplegic migraine attacks, behavioral dysregulation, and EEG abnormalities. The mother showed typical episodic ataxia attacks during infancy with no other comorbidities and mild cerebellar signs at present neurological evaluation. CONCLUSIONS: The proband and his mother exhibit two distinct clinical phenotypes. It can be hypothesized that other unknown modifying genes and/or environmental factors may cooperate to generate the wide intrafamilial variability.

Migraine in children under 6 years of age: A long-term follow-up study.

BACKGROUND: Early starting of migraine seems predictive for less favorable outcome in later ages, however follow-up investigations are very few and all with short-term prospective period. We report here the longest follow-up study in a population of children presenting with migraine under the age of 6. METHODS: We followed-up 74 children under 6 years of age, referred for headache to our department between 1997 and 2003. The study was carried out between October 2016 and March 2018. Headache diagnoses were made according to the IHS criteria. RESULTS: 23/74 patients, 31% of the original cohort, were found at follow-up in a period ranging between 15 to 21 years after the first visit. Seven of them were headache free. The remaining 16 patients had migraine. In the migraine group, the localization of pain changed in 75% of the subjects, 11/16 (68.7%) had allodynia and 9/16 (56.25%) had cranial autonomic symptoms. CONCLUSIONS: Our results suggest that the onset of migraine at very young age represents unfavorable prognostic factor for persistence of the disease at later ages. Some clinical features may change during clinical course, and the active persistence of the disorder may lead to an increase in allodynia.

Neuropeptides' Hypothalamic Regulation of Sleep Control in Children Affected by Functional Non-Retentive Fecal Incontinence.

Functional non-retentive fecal incontinence (FNRFI) is a common problem in pediatric age. FNRFI is defined as unintended loss of stool in a 4-year-old or older child after organic causes have been excluded. FNRFI tends to affects up to 3% of children older than 4 years, with males being affected more frequently than females. Clinically, children affected by FNRFI have normal intestinal movements and stool consistency. Literature data show that children with fecal incontinence have increased levels of separation anxiety, specific phobias, general anxiety, attention-deficit/hyperactivity disorder (ADHD), and oppositional defiant disorder. In terms of possible relationship between incontinence and sleep, disorders of sleep organization have been observed in the pathogenesis of enuresis so generating the hypothesis that the orexinergic system may have a crucial role not only for the sleep organization per se but also for the sphincterial control in general. This study aimed to focus on specific neurophysiological aspects to investigate on the possible relationship between sleep organizational abnormalities and FNRFI. Specifically, we aimed to measure orexin serum levels in children with FNRFI and assess their polysomnographic sleep macrostructure patterns. Two study groups were considered: FNFRI (n = 45) and typically developed (TD) (n = 45) group. In both groups, sleep patterns and respiratory events were assessed by polysomnographic recordings (PSG) during a period of two nights at least, and plasma levels of Orexin-A were measured in each participant. The findings of this initial investigation seem to support a major role of Orexin-A in sleep organization alterations in children with FNFRI. Also, our data suggest that sleep habits evaluation should be considered as screening and complementary tool for the diagnosis of fecal incontinence in children.

Age-dependent epileptic encephalopathy associated with an unusual co-occurrence of ZEB2 and SCN1A variants.

Mowat-Wilson syndrome is a genetic disorder associated with a variable phenotype including peculiar facial features associated with intellectual disability, epilepsy, language impairment, and multiple congenital anomalies caused by heterozygous mutation of the ZEB2 gene. The ZEB2 protein is a complex transcription factor that encompasses multiple functional domains that interact with the regulatory regions of target genes including those involved in brain development. Recently, it has been documented that ZEB2 regulates the differentiation of interneuron progenitors migrating from the medial ganglionic eminence to cortical layers by repression of the Nkx2-1 homeobox transcription factor. It has therefore been suggested that the deficit in ZEB2 may induce an imbalance of neuronal inhibition/excitation leading to epileptic seizures. Given the phenotypic variability of Mowat-Wilson syndrome, to date, a distinctive genotype-phenotype correlation has not been delineated. Here, we report a patient with a severe phenotype of Mowat-Wilson syndrome, associated with a novel heterozygous de novo frame-shift variant in the ZEB2 gene, as well as an additional novel heterozygous missense variant in the SCN1A gene, the mutation of which is known to affect NaV1.1-mediated sodium current in GABAergic interneurons. We hypothesize that the severe neurological phenotype of our patient may be influenced by the coexistence of both genetic mutations. [Published with video sequence].

The largest caucasian kindred with dentatorubral-pallidoluysian atrophy: A founder mutation in italy.

BACKGROUND: Dentatorubral-pallidoluysian atrophy is a hereditary neurodegenerative disease prevalently reported in Japan but rare in Caucasians. The objective of this study was to reconstruct the pedigree of Italian dentatorubral-pallidoluysian atrophy familial cases describing their clinical features. METHODS: We investigated 6 apparently unrelated dentatorubral-pallidoluysian atrophy families comprising a total of 51 affected individuals: 13 patients were clinically examined, and for 38 patients clinical data were collected from clinical sources. The dentatorubral-pallidoluysian atrophy diagnosis was genetically confirmed in 18 patients. Genealogical data from historical archives were analyzed. RESULTS: All 6 families were unified in a large pedigree deriving from a founder couple originating from Monte San Giuliano (Italy) in the late 1500s, with 51 affected subjects over the last 4 generations. Wide phenotypical variability in age at onset and clinical features was confirmed. Epilepsy was more frequent in juvenile cases than in late adults, with cognitive/psychiatric and motor disorders observed regardless of age at onset. CONCLUSIONS: We have described the largest Caucasian dentatorubral-pallidoluysian atrophy pedigree from a single founder couple. The introduction of the dentatorubral-pallidoluysian atrophy gene in Italy could have arisen as a result of trade relationships between the Spanish or Portuguese and the Japanese in the 1500s. © 2019 International Parkinson and Movement Disorder Society.

A novel mutation in KCNQ3-related benign familial neonatal epilepsy: electroclinical features and neurodevelopmental outcome.

Benign familial neonatal epilepsy (BFNE) is caused, in about 5% of families, by mutations in the KCNQ3 gene encoding voltage-gated potassium channel subunits. Usually, newborns with BFNE show a normal neurological outcome, but recently, refractory seizures and/or developmental disability have been reported suggesting phenotype variability associated with KCNQ3-related BFNE. Here, we describe a proband from a BFNE family carrying a novel variant in the KCNQ3 gene. Regarding the paucity of data in the literature, we describe the presented case with a view to further establishing: (1) a genotype/phenotype correlation in order to define a BFNE phenotype associated with favourable outcome; (2) an electroclinical pattern associated with BFNE based on video-EEG recording; (3) appropriate first-line AEDs; and (4) the duration of AED treatment. The presented case from Day 3 exhibited a cluster of ictal events, identified as epileptic seizures on Day 10 based on continuous video-EEG polygraphy. The seizures were characterized by asymmetric tonic posturing, associated with a generalized decrease in EEG amplitude, and followed by bilateral asynchronous clonic movements associated with bicentral sharp-wave discharges. The seizures were refractory to intravenous pyridoxine, whereas levetiracetam resulted in rapid total seizure control which has remained to date. This study demonstrates that the novel heterozygous KCNQ3 (c. 914A>T; p.Asp305Val) variant, affecting residues in the pore region, is associated with a specific electroclinical pattern and favourable neurodevelopmental outcome. [Published with video sequence on www.epilepticdisorders.com].