Structural brain abnormalities in Pallister-Killian syndrome: a neuroimaging study of 31 children.

BACKGROUND: Pallister-Killian syndrome (PKS) is a rare genetic disorder caused by mosaic tetrasomy of 12p with wide neurological involvement. Intellectual disability, developmental delay, behavioral problems, epilepsy, sleep disturbances, and brain malformations have been described in most individuals, with a broad phenotypic spectrum. This observational study, conducted through brain MRI scan analysis on a cohort of patients with genetically confirmed PKS, aims to systematically investigate the neuroradiological features of this syndrome and identify the possible existence of a typical pattern. Moreover, a literature review differentiating the different types of neuroimaging data was conducted for comparison with our population. RESULTS: Thirty-one individuals were enrolled (17 females/14 males; age range 0.1-17.5 years old at first MRI). An experienced pediatric neuroradiologist reviewed brain MRIs, blindly to clinical data. Brain abnormalities were observed in all but one individual (compared to the 34% frequency found in the literature review). Corpus callosum abnormalities were found in 20/30 (67%) patients: 6 had callosal hypoplasia; 8 had global hypoplasia with hypoplastic splenium; 4 had only hypoplastic splenium; and 2 had a thin corpus callosum. Cerebral hypoplasia/atrophy was found in 23/31 (74%) and ventriculomegaly in 20/31 (65%). Other frequent features were the enlargement of the cisterna magna in 15/30 (50%) and polymicrogyria in 14/29 (48%). Conversely, the frequency of the latter was found to be 4% from the literature review. Notably, in our population, polymicrogyria was in the perisylvian area in all 14 cases, and it was bilateral in 10/14. CONCLUSIONS: Brain abnormalities are very common in PKS and occur much more frequently than previously reported. Bilateral perisylvian polymicrogyria was a main aspect of our population. Our findings provide an additional tool for early diagnosis.Further studies to investigate the possible correlations with both genotype and phenotype may help to define the etiopathogenesis of the neurologic phenotype of this syndrome.

Cellular Strategies for Separating GvHD from GvL in Haploidentical Transplantation.

GvHD still remains, despite the continuous improvement of transplantation platforms, a fearful complication of transplantation from allogeneic donors. Being able to separate GvHD from GvL represents the greatest challenge in the allogeneic transplant setting. This may be possible through continuous improvement of cell therapy techniques. In this review, current cell therapies are taken into consideration, which are based on the use of TCR alpha/beta depletion, CD45RA depletion, T regulatory cell enrichment, NK-cell-based immunotherapies, and suicide gene therapies in order to prevent GvHD and maximally amplify the GvL effect in the setting of haploidentical transplantation.

Electroclinical features and phenotypic differences in adenylosuccinate lyase deficiency: Long-term follow-up of seven patients from four families and appraisal of the literature.

OBJECTIVE: Adenylosuccinate lyase (ADSL) deficiency is a rare inherited metabolic disorder with a wide phenotypic presentation, classically grouped into three types (neonatal, type I, and type II). We aim to better delineate the pathological spectrum, focusing on the electroclinical characteristics and phenotypic differences of patients with ADSL deficiency. PATIENTS AND METHODS: Seven patients, from four different families, underwent serial electroencephalogram (EEG), clinical assessment, and neuroimaging. We also performed a systematic review of the cases published in the literature, summarizing the available clinical, neurophysiological, and genetic data. RESULTS: We report seven previously unreported ADSL deficiency patients with long-term follow-up (10-34 years). From the literature review, we collected 81 previously reported cases. Of the included patient population, 58 % (51/88) were classified as having ADSL deficiency type I, 28% (25/88) as having type II, and 14% (12/88) as having neonatal. The most frequently reported pathogenic variants are p.R426H homozygous (19 patients), p.Y114H in compound heterozygosity (13 patients), and p.D430N homozygous (6 patients). In the majority (89.2%), disease onset was within the first year of life. Epilepsy is present in 81.8% of the patients, with polymorphic and often intractable seizures. EEG features seem to display common patterns and developmental trajectories: (i) poor general background organization with theta-delta activity; (ii) hypsarrhythmia with spasms, usually adrenocorticotropic hormone-responsive; (iii) generalized epileptic discharges with frontal or frontal temporal predominance; and (iv) epileptic discharge activation in sleep with an altered sleep structure. Imaging features present consistent findings of cerebral atrophy with frontal predominance, cerebellar atrophy, and white matter abnormalities among the three types. SIGNIFICANCE: ADSL deficiency presents variable phenotypic expression, whose severity could be partially attributed to residual activity of the mutant protein. Although a precise phenotype-genotype correlation was not yet feasible, we delineated a common pattern of clinical, neuroradiological, and neurophysiological features.

Fate of melatonin orally administered in preterm newborns: Antioxidant performance and basis for neuroprotection.

Preterm infants cannot counteract excessive reactive oxygen species (ROS) production due to preterm birth, leading to an excess of lipid peroxidation with malondialdehyde (MDA) production, capable of contributing to brain damage. Melatonin (ME), an endogenous brain hormone, and its metabolites, act as a free radical scavenger against ROS. Unfortunately, preterms have an impaired antioxidant system, resulting in the inability to produce and release ME. This prospective, multicenter, parallel groups, randomized, double-blind, placebo-controlled trial aimed to assess: (i) the endogenous production of ME in very preterm infants (gestational age ≤ 29 + 6 WE, 28 infants in the ME and 26 in the placebo group); (ii) the exogenous hormone availability and its metabolization to the main metabolite, 6-OH-ME after 15 days of ME oral treatment; (iii) difference of MDA plasma concentration, as peroxidation marker, after treatment. Blood was collected before the first administration (T1) and after 15 days of administration (T2). ME and 6-OH-ME were detected by liquid chromatography tandem mass spectrometry, MDA was measured by liquid chromatograph with fluorescence detection. ME and 6-OH-ME were not detectable in the placebo group at any study time-point. ME was absent in the active group at T1. In contrast, after oral administration, ME and 6-OH-ME resulted highly detectable and the difference between concentrations T2 versus T1 was statistically significant, as well as the difference between treated and placebo groups at T2. MDA levels seemed stable during the 15 days of treatment in both groups. Nevertheless, a trend in the percentage of neonates with reduced MDA concentration at T2/T1 was 48.1% in the ME group versus 38.5% in the placebo group. We demonstrated that very preterm infants are not able to produce endogenous detectable plasma levels of ME during their first days of life. Still, following ME oral administration, appreciable amounts of ME and 6-OH-ME were available. The trend of MDA reduction in the active group requires further clinical trials to fix the dosage, the length of ME therapy and to identify more appropriate indexes to demonstrate, at biological and clinical levels, the antioxidant activity and consequent neuroprotectant potential of ME in very preterm newborns.

Daratumumab-based induction and autologous transplantation in concomitant multiple myeloma and chronic myeloid leukemia.

The coexistence of chronic myeloid leukemia (CML) and multiple myeloma (MM) is a rare clinical condition. By means of FISH and molecular analysis on both sorted CD138 plasma cells and cryopreserved CD34 stem cells, a distinct clonal origin of the hematological malignancies was demonstrated in our case. We report on the first patient diagnosed with CML and MM treated with daratumumab, bortezomib, thalidomide, and dexamethasone (Dara-VTd) induction, stem-cell collection, and autologous stem cell transplantation (ASCT). The co-administration of Dara-VTd and imatinib proved feasible and highly effective in the management of both CML and MM. Despite concerns with stem cell mobilization and collection in patients exposed to daratumumab, in our experience the use of higher cyclophosphamide dose 4 g/m2 together with plerixafor granted optimal stem cell mobilization and collection, irrespective of daratumumab, concomitant myeloid neoplasm, and imatinib. Moreover, ASCT was easily performed with a rapid hematological reconstitution.

Frequency of SCN2A-related disorder in the regional epilepsy centre of brescia between 2002 and 2021.

OBJECTIVE: SCN2A gene pathogenic variants are associated with a wide phenotypic spectrum, encompassing epilepsy, developmental delay, and autism spectrum disorder. Researches conducted in Denmark have revealed a disease frequency of approximately 1/78,608 (0.0012%) live births in this population. We estimated the frequency of SCN2A-related disorder in the birth cohort of Brescia and its province between 2002 and 2021. METHODS: Frequency was calculated by ratio between patients with SCN2A pathogenic variant and the total number of live births at the Regional Epilepsy Center of Brescia, between 2002 and 2021. The number of births in Brescia and province was obtained from the Italian National Institute of Statistics (ISTAT). RESULTS: A frequency of 11/23,2678 births (0.0047%) was found. In comparison with Danish data, we noticed a higher frequency of the pathogenic variant in our population, even considering the same time frame (0.0035% of subjects born between 2006 and 2014). CONCLUSION: The frequency of SCN2A pathogenic variant among live births in Brescia and its Province between 2006 and 2014 was about three times that of Danish population; this difference was about four times if we consider the period from 2002 to 2021. More studies are needed to further delineate the frequency of SCN2A pathogenic variant in Italian population.

Long-Term Visual and Neurodevelopmental Outcomes in Two Children with Congenital Nystagmus Secondary to Methadone Exposure In utero.

Methadone is used as a substitute for illicit opioids during pregnancy. However, the real effect of this molecule on visual and neurodevelopmental outcomes of the children exposed is not fully understood, since studies considered subjects born to polydrug-dependent mothers and followed for few months/years. We report the long-term outcomes of two infants with congenital nystagmus solely exposed to methadone in utero. Neurological and neurovisual evaluations were performed every year from the first year of life to 11 years of age. One child was diagnosed with developmental coordination disorder. Both cases presented with ophthalmologic (refractive errors), oculomotor (nystagmus and fixation, smooth pursuit, and saccades dysfunctions), and perceptive problems (reduced visual acuity and contrast sensitivity). While nystagmus and other oculomotor dysfunctions remained stable over time, visual acuity and contrast sensitivity improved; refractive errors worsened and required corrective lenses. Both children showed normal neurodevelopmental and cognitive profile. This report highlights the long-term visual and developmental outcomes of two children exclusively exposed to methadone underlining the possibility of a visual dysfunction and motor coordination disorder. These observations prompt the need to investigate prenatal drug exposure as a cause of congenital nystagmus.

Severe Streptococcus equi Subspecies zooepidemicus Outbreak from Unpasteurized Dairy Product Consumption, Italy.

During November 2021-May 2022, we identified 37 clinical cases of Streptococcus equi subspecies zooepidemicus infections in central Italy. Epidemiologic investigations and whole-genome sequencing showed unpasteurized fresh dairy products were the outbreak source. Early diagnosis by using sequencing technology prevented the spread of life-threatening S. equi subsp. zooepidemicus infections.

A PUS7 gene pathogenic variant causing self-injurious behavior, sleep disturbances, and developmental delay: A case report.

PUS7 gene pathogenic variants cause a deficiency in an RNA-independent pseudouridine synthase, which results in a neurodevelopmental phenotype characterized by various degrees of psychomotor delay, acquired microcephaly, aggressive behavior, and intellectual disability. Since 2018, PUS7 deficiency has been described in 15 patients with different pathogenic variants but similar clinical phenotypes. We describe the case of a male infant with a homozygous truncating pathogenic variant in the PUS7 gene (c.329_332delCTGA; p.Thr110Argfs*4) who, in addition to the previously mentioned features, displays self-injurious behavior, sleep disturbances and motor stereotypies.

A registry for Dravet syndrome: The Italian experience.

OBJECTIVES: We describe the Residras registry, dedicated to Dravet syndrome (DS) and to other phenotypes related to SCN1A mutations, as a paradigm of registry for rare and complex epilepsies. Our primary objectives are to present the tools and framework of the integrative platform, the main characteristics emerging from the patient cohort included in the registry, with emphasis on demographic, clinical outcome, and mortality. METHODS: Standardized data of enrolled pediatric and adult patients were collected in 24 Italian expert centers and regularly updated at least on a yearly basis. Patients were prospectively enrolled, at registry starting, but historical retrospective data were also included. RESULTS: At present, 281 individuals with DS and a confirmed SCN1A mutation are included. Most patients have data available on epilepsy (n = 263) and their overall neurological condition (n = 255), based on at least one follow-up update. Median age at first clinical assessment was 2 years (IQR 0-9) while at last follow-up was 11 years (IQR 5-18.5). During the 7-year activity of the registry, five patients died resulting in a mortality rate of 1.84 per 1000-person-years. When analyzing clinical changes over the first 5-year follow-up, we observed a significant difference in cognitive function (P < 0.001), an increased prevalence of behavioral disorders including attention deficit (P < 0.001), a significant worsening of language (P = 0.001), and intellectual disability (P < 0.001). SIGNIFICANCE: The Residras registry represents a large collection of standardized national data for the DS population. The registry platform relies on a shareable and interoperable framework, which promotes multicenter high-quality data collection. In the future, such integrated platform may represent an invaluable asset for easing access to cohorts of patients that may benefit from clinical trials with emerging novel therapies, for drug safety monitoring, and for delineating natural history. Its framework makes it improvable based on growing experience with its use and easily adaptable to other rare and complex epilepsy syndromes.

BORN study: a multicenter randomized trial investigating cord blood red blood cell transfusions to reduce the severity of retinopathy of prematurity in extremely low gestational age neonates.

BACKGROUND: Extremely low gestational age neonates (ELGANs, i.e., neonates born before 28 weeks of gestation) are at high risk of developing retinopathy of prematurity (ROP), with potential long-life visual impairment. Due to concomitant anemia, ELGANs need repeated red blood cell (RBC) transfusions. These produce a progressive replacement of fetal hemoglobin (HbF) by adult hemoglobin (HbA). Furthermore, a close association exists between low levels of HbF and severe ROP, suggesting that a perturbation of the HbF-mediated oxygen release may derange retinal angiogenesis and promote ROP. METHODS/DESIGN: BORN (umBilical blOod to tRansfuse preterm Neonates) is a multicenter double-blinded randomized controlled trial in ELGANs, to assess the effect of allogeneic cord blood RBC transfusions (CB-RBCs) on severe ROP development. Recruitment, consent, and randomization take place at 10 neonatology intensive care units (NICUs) of 8 Italian tertiary hospitals. ELGANs with gestational age at birth comprised between 24+0 and 27+6 weeks are randomly allocated into two groups: (1) standard RBC transfusions (adult-RBCs) (control arm) and (2) CB-RBCs (intervention arm). In case of transfusion need, enrolled patients receive transfusions according to the allocation arm, unless an ABO/RhD CB-RBC is unavailable. Nine Italian public CB banks cooperate to make available a suitable amount of CB-RBC units for all participating NICUs. The primary outcome is the incidence of severe ROP (stage 3 or higher) at discharge or 40 weeks of postmenstrual age, which occurs first. DISCUSSION: BORN is a groundbreaking trial, pioneering a new transfusion approach dedicated to ELGANs at high risk for severe ROP. In previous non-randomized trials, this transfusion approach was proven feasible and able to prevent the HbF decrease in patients requiring multiple transfusions. Should the BORN trial confirm the efficacy of CB-RBCs in reducing ROP severity, this transfusion strategy would become the preferential blood product to be used in severely preterm neonates. TRIAL REGISTRATION: ClinicalTrials.gov NCT05100212. Registered on October 29, 2021.

EEG at onset and MRI predict long-term clinical outcome in Aicardi syndrome.

OBJECTIVE: Descriptions of electroencephalographic (EEG) patterns in Aicardi syndrome (AIC) have to date referred to small cohorts of up to six cases and indicated severe derangement of electrical activity in all cases. The present study was conducted to describe the long-term EEG evolution in a larger AIC cohort, followed for up to 23 years, and identify possible early predictors of the clinical and EEG outcomes. METHODS: In a retrospective study, two experienced clinical neurophysiologists systematically reviewed all EEG traces recorded in 12 AIC cases throughout their follow-up, from epilepsy onset to the present. Clinical outcome was assessed with standardized clinical outcome scales. RESULTS: Analysis of the data revealed two distinct AIC phenotypes. In addition to the "classical severe phenotype" already described in the literature, we identified a new "mild phenotype". The two phenotypes show completely different EEG features at onset of epilepsy and during its evolution, which correspond to different clinical outcomes. CONCLUSIONS: Data from our long-term EEG and clinical-neuroradiological study allowed us to describe two different phenotypes of AIC, with different imaging severity and, in particular, different EEG at onset, which tend to remain constant over time. SIGNIFICANCE: Together, these findings might help to predict long-term clinical outcomes.

Epilepsy Course and Developmental Trajectories in STXBP1-DEE.

Background and Objectives: Clinical manifestations in STXBP1 developmental and epileptic encephalopathy (DEE) vary in severity and outcome, and the genotypic spectrum is diverse. We aim to trace the neurodevelopmental trajectories in individuals with STXBP1-DEE and dissect the relationship between neurodevelopment and epilepsy. Methods: Retrospective standardized clinical data were collected through international collaboration. A composite neurodevelopmental score system compared the developmental trajectories in STXBP1-DEE. Results: Forty-eight patients with de novo STXBP1 variants and a history of epilepsy were included (age range at the time of the study: 10 months to 35 years, mean 8.5 years). At the time of inclusion, 65% of individuals (31/48) had active epilepsy, whereas 35% (17/48) were seizure free, and 76% of those (13/17) achieved remission within the first year of life. Twenty-two individuals (46%) showed signs of developmental impairment and/or neurologic abnormalities before epilepsy onset. Age at seizure onset correlated with severity of developmental outcome and the developmental milestones achieved, with a later seizure onset associated with better developmental outcome. In contrast, age at seizure remission and epilepsy duration did not affect neurodevelopmental outcomes. Overall, we did not observe a clear genotype-phenotype correlation, but monozygotic twins with de novo STXBP1 variant showed similar phenotype and parallel disease course. Discussion: The disease course in STXBP1-DEE presents with 2 main trajectories, with either early seizure remission or drug-resistant epilepsy, and a range of neurodevelopmental outcomes from mild to profound intellectual disability. Age at seizure onset is the only epilepsy-related feature associated with neurodevelopment outcome. These findings can inform future dedicated natural history studies and trial design.

Repetitive and stereotyped behaviors in neurodevelopmental disorders: an observational analysis of four diagnostic groups.

BACKGROUND: Repetitive and Stereotyped Behaviors (ST) are one of the key features of autism spectrum disorder (ASD) and they frequently occur in children with developmental delay/intellectual disability or sensory deprivation, but they are also described in children otherwise typical. This study aims to describe and compare ST in children with different neurodevelopmental disorders and in children having stereotypies but no other medical diagnosis (primary stereotypies). METHODS: The study sample comprised children with autism spectrum disorder (ASD) developmental delay (DD), severe visual impairment (VI) and primary stereotypies (PS), aged between 2 and 12 years old. The characteristics of the ST (age of onset, frequency, duration, triggers, phenomenology) were collected from their clinical history. The children's caregivers completed the Repetitive Behavior Scalerevised (RBS-R) and the Child Behavior Checklist (CBCL) to assess the ST and to screen for behavioral problems, respectively. Data concerning family history and comorbidity were also collected. RESULTS: 87 children (ASD [n=23]; DD [n=21]; VI [n=20]; PS [n=23]) were assessed. Mean age of ST onset was before 24 months in the whole sample. Symptoms usually occurred more than once a day in all groups, but Self-Injurious Behavior (SIB) and ST were reported at higher scores on the RBS-R in Secondary group. Stereotypies lasted less than 5 minutes in all but VI sample, in which lasted longer. Stereotypies of locomotion were mostly reported in ASD, self-injurious behaviors in VI, upper limb stereotypies in PS and DD. Parents reported several repetitive behaviors on the RBS-R, while attention deficit and withdrawn behavior appeared to be the main findings of the sample in the CBCL. Finally, a high number of comorbidities and family history for neurodevelopmental disorders was found in all groups. CONCLUSIONS: The study showed that some specific patterns of stereotypies could be identified in most groups of disorders. At the same time the behavioral profile of children with stereotypies shows a significant overlap among different groups. These preliminary results suggest that stereotypies are strongly linked to neurodevelopmental disorders, but their association needs to be clarified with further studies.

Pediatric Moyamoya Disease and Syndrome in Italy: A Multicenter Cohort.

Background: Moyamoya is a rare progressive cerebral arteriopathy, occurring as an isolated phenomenon (moyamoya disease, MMD) or associated with other conditions (moyamoya syndrome, MMS), responsible for 6-10% of all childhood strokes and transient ischemic attacks (TIAs). Methods: We conducted a retrospective multicenter study on pediatric-onset MMD/MMS in Italy in order to characterize disease presentation, course, management, neuroradiology, and outcome in a European country. Results: A total of 65 patients (34/65 women) with MMD (27/65) or MMS (38/65) were included. About 18% (12/65) of patients were asymptomatic and diagnosed incidentally during investigations performed for an underlying condition (incMMS), whereas 82% (53/65) of patients with MMD or MMS were diagnosed due to the presence of neurological symptoms (symptMMD/MMS). Of these latter, before diagnosis, 66% (43/65) of patients suffered from cerebrovascular events with or without other manifestations (ischemic stroke 42%, 27/65; TIA 32%, 21/65; and no hemorrhagic strokes), 18% (12/65) of them reported headache (in 4/12 headache was not associated with any other manifestation), and 26% (17/65) of them experienced multiple phenotypes (≥2 among: stroke/TIA/seizures/headache/others). Neuroradiology disclosed ≥1 ischemic lesion in 67% (39/58) of patients and posterior circulation involvement in 51% (30/58) of them. About 73% (47/64) of patients underwent surgery, and 69% (45/65) of them received aspirin, but after diagnosis, further stroke events occurred in 20% (12/61) of them, including operated patients (11%, 5/47). Between symptom onset and last follow-up, the overall patient/year incidence of stroke was 10.26% (IC 95% 7.58-13.88%). At last follow-up (median 4 years after diagnosis, range 0.5-15), 43% (26/61) of patients had motor deficits, 31% (19/61) of them had intellectual disability, 13% (8/61) of them had epilepsy, 11% (7/61) of them had behavioral problems, and 25% (13/52) of them had mRS > 2. The proportion of final mRS > 2 was significantly higher in patients with symptMMD/MMS than in patients with incMMS (p = 0.021). Onset age <4 years and stroke before diagnosis were significantly associated with increased risk of intellectual disability (p = 0.0010 and p = 0.0071, respectively) and mRS > 2 at follow-up (p = 0.0106 and p = 0.0009, respectively). Conclusions: Moyamoya is a severe condition that may affect young children and frequently cause cerebrovascular events throughout the disease course, but may also manifest with multiple and non-cerebrovascular clinical phenotypes including headache (isolated or associated with other manifestations), seizures, and movement disorder. Younger onset age and stroke before diagnosis may associate with increased risk of worse outcome (final mRS > 2).

Genotype-phenotype correlations in SCN8A-related disorders reveal prognostic and therapeutic implications.

We report detailed functional analyses and genotype-phenotype correlations in 392 individuals carrying disease-causing variants in SCN8A, encoding the voltage-gated Na+ channel Nav1.6, with the aim of describing clinical phenotypes related to functional effects. Six different clinical subgroups were identified: Group 1, benign familial infantile epilepsy (n = 15, normal cognition, treatable seizures); Group 2, intermediate epilepsy (n = 33, mild intellectual disability, partially pharmaco-responsive); Group 3, developmental and epileptic encephalopathy (n = 177, severe intellectual disability, majority pharmaco-resistant); Group 4, generalized epilepsy (n = 20, mild to moderate intellectual disability, frequently with absence seizures); Group 5, unclassifiable epilepsy (n = 127); and Group 6, neurodevelopmental disorder without epilepsy (n = 20, mild to moderate intellectual disability). Those in Groups 1-3 presented with focal or multifocal seizures (median age of onset: 4 months) and focal epileptiform discharges, whereas the onset of seizures in patients with generalized epilepsy was later (median: 42 months) with generalized epileptiform discharges. We performed functional studies expressing missense variants in ND7/23 neuroblastoma cells and primary neuronal cultures using recombinant tetrodotoxin-insensitive human Nav1.6 channels and whole-cell patch-clamping. Two variants causing developmental and epileptic encephalopathy showed a strong gain-of-function (hyperpolarizing shift of steady-state activation, strongly increased neuronal firing rate) and one variant causing benign familial infantile epilepsy or intermediate epilepsy showed a mild gain-of-function (defective fast inactivation, less increased firing). In contrast, all three variants causing generalized epilepsy induced a loss-of-function (reduced current amplitudes, depolarizing shift of steady-state activation, reduced neuronal firing). Functional effects were known for 170 individuals. All 136 individuals carrying a functionally tested gain-of-function variant had either focal (n = 97, Groups 1-3) or unclassifiable (n = 39) epilepsy, whereas 34 individuals with a loss-of-function variant had either generalized (n = 14), no (n = 11) or unclassifiable (n = 6) epilepsy; only three had developmental and epileptic encephalopathy. Computational modelling in the gain-of-function group revealed a significant correlation between the severity of the electrophysiological and clinical phenotypes. Gain-of-function variant carriers responded significantly better to sodium channel blockers than to other anti-seizure medications, and the same applied for all individuals in Groups 1-3. In conclusion, our data reveal clear genotype-phenotype correlations between age at seizure onset, type of epilepsy and gain- or loss-of-function effects of SCN8A variants. Generalized epilepsy with absence seizures is the main epilepsy phenotype of loss-of-function variant carriers and the extent of the electrophysiological dysfunction of the gain-of-function variants is a main determinant of the severity of the clinical phenotype in focal epilepsies. Our pharmacological data indicate that sodium channel blockers present a treatment option in SCN8A-related focal epilepsy with onset in the first year of life.