A comprehensive understanding of the clinical spectrum and genotype-phenotype correlation in KCNT1-related disorders is offered and the need to develop multisource data methodologies and registries to reduce follow-up loss in real-world data collections based on health records is highlighted.
Abstract
Abstract The KCNT1 gene encodes for a sodium-activated potassium channel involved in neuronal excitability. Since its initial description in 2012 in patients with Epilepsy of Infancy with Migrating Focal Seizures (EIMFS) and in Sleep-related Hypermotor Epilepsy (SHE), the associated phenotypic spectrum has broadened—encompassing other focal epilepsies and Developmental and Epileptic Encephalopathies (DEEs)—and has included extra-neurological features. We aimed to characterize the neurological outcomes, extra-neurological features, mortality and genotype-phenotype correlations expanding the follow-up of the reported cases with KCNT1 variants. A comprehensive literature review was performed to identify all reported cases of KCNT1 pathogenic or likely pathogenic variants. Corresponding authors were contacted to obtain updated clinical data, including current vital status, epilepsy progression, extra-neurological features, cognitive and psychiatric status. The entire dataset, including updated data from the literature, was combined for subsequent analyses. A total of 316 patients from 88 publications were included. Follow-up data were obtained for 60 patients (from 28 papers and 11 countries), increasing the median age at last assessment from 4.4 to 6.0 years. 181 patients had an EIMFS phenotype, 62 had SHE, and 59 had various DEEs. Five individuals were asymptomatic parents, six had other focal epilepsies, and three had other phenotypes. Extra-neurological features were predominantly observed in patients with EIMFS and DEE, notably systemic-to-pulmonary collateral arteries, other vascular or cardiac malformations and various respiratory, orthopaedic or gastrointestinal disorders. The main cause of death was pulmonary complications (haemorrhage or infection). Genotype–phenotype correlations revealed a trend for variants in the first regulator of conductance of potassium (RCK1) domain to associate with EIMFS/non-EIMFS DEE, while SHE-associated variants were predominantly located in the second regulator of conductance of potassium (RCK2) domain. Additionally, variants p.Arg474Cys may confer increased risk for vascular malformations, but the issue appears to be broader, and systematic screening of patients carrying pathogenic KCNT1 variants would allow us to better define this risk. This study offers a comprehensive understanding of the clinical spectrum and genotype-phenotype correlation in KCNT1-related disorders. This study has inherent biases related to the retrospective collection of already published data and underscores the need to develop multisource data methodologies and registries to reduce follow-up loss in real-world data collections based on health records.
Background and Objectives KCNT1-related epilepsy is an ultra-rare pediatric-onset developmental and epileptic encephalopathy with a broad clinical phenotype ranging from, most commonly, severe infantile-onset epilepsy and global developmental delay to, less commonly, milder phenotypes including sleep-related seizures, autism spectrum disorder, and learning disability. We initiated the first-ever prospective natural history study to comprehensively clinically phenotype individuals affected by this disorder. Methods The primary aim of this study was to characterize seizures in individuals with KCNT1-related epilepsy. Secondary and exploratory aims included characterization of the full spectrum of disease symptoms, understanding caregiver burden, and collection of blood and urine samples for biomarker exploration. All study activities were conducted remotely (e.g., home-based assessments, telehealth visits). Results Thirty-five participants (n = 20 male, 15 female) were enrolled in this study. The average age at the baseline visit was 76.0 months (s.d. = 75.5). This article presents the study design and methods and several challenges that arose in its implementation and discusses various solutions implemented in this medically complex population. Discussion Future work will apply the lessons from this study in the planning and design of clinical trials for KCNT1-related epilepsy and possibly other developmental and epileptic encephalopathies.
Heather R. Adams, Viet Nguyen, L. Seltzer et al.· Neurology: Genetics· 0 citations
The electroclinical and developmental features of three patients carrying truncating TANC2 variants identified through trio‐exome sequencing within the European collaborative platform NETRE are described, expanding the known clinical spectrum of TANC2‐related disorders and suggesting that selected patients may have a more favorable seizure course than expected.
L. Perilli, Carlotta Stipa, Gianmichele Villano et al.· Epilepsia Open· 0 citations
Pathogenic KCNQ2 variants are the most common genetic cause of neonatal-onset epilepsies, with phenotypes ranging from self-limited (familial) neonatal epilepsy (SeL(F)NE) to severe developmental and epileptic encephalopathy (KCNQ2-DEE). Sodium channel blockers (SCBs) have shown promise for seizure control in these disorders, but their impact on neurodevelopmental outcomes and possible relationship with timing of initiation remain incompletely understood. We leveraged a large, multicentre international cohort comprising 282 individuals with pathogenic KCNQ2 variants to retrospectively assess the effectiveness of antiseizure medications (ASMs), particularly SCBs, on seizure control and neurodevelopment. Individuals were grouped according to the predicted variant-specific functional effects: loss-of-function (LOF) variants known to be associated with SeL(F)NE or DEE respectively, and gain-of-function (GOF) variants. Epilepsy course, ASM effectiveness, and neurodevelopmental milestones were systematically collected and analysed, including time-to-event and adjusted outcome analyses. SCBs, especially carbamazepine (CBZ) and oxcarbazepine (OXC), emerged as the most effective ASMs in both LOF groups. In LOF KCNQ2-DEE, time-to-event analyses showed that early SCB initiation (≤1 month) was associated with earlier seizure offset. Early SCB initiation was also associated with significantly more favourable neurodevelopmental outcomes, including higher rates of attaining major motor milestones. This association remained significant after adjustment for seizure control by 1 month and total ASM burden. Considerable phenotypic variability persisted, with some individuals experiencing severe impairment despite early seizure control and SCB initiation, suggesting that variant severity and additional genetic or biological modifiers contribute to outcome heterogeneity.Our results support the use of SCBs, particularly CBZ and OXC, as first-line therapy in (LOF) KCNQ2-DEE and SeL(F)NE. Earlier SCB initiation was associated with earlier seizure offset and more favourable developmental outcomes, underscoring the importance of early genetic diagnosis and timely SCB therapy. We however emphasise that early treatment is not universally transformative and further prospective work, including exploration of targeted therapies and standardised neurodevelopmental assessments, is needed to optimise long-term outcomes in this heterogeneous population.
C. Millevert, M. Hairabedian, Samuel Dahan et al.· Brain : a journal of neurolo...· 0 citations
The findings support a possible domain‐related genotype–phenotype association for the role of ALG13 in neurodevelopmental disorders and provide additional developmental context for the role of ALG13 in neurodevelopmental disorders.
Song Su, Wandong Hu, Ying Ren et al.· Human Mutation· 0 citations
Background and Objectives ATP1A3-related disorders comprise an expanding group of ultra-rare neurologic conditions, classically including rapid-onset dystonia-parkinsonism (RDP), alternating hemiplegia of childhood (AHC), and cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS) syndrome. However, accumulating reports suggest a broader and overlapping phenotypic spectrum. In this context, we established the ATP1A3 Study Group to comprehensively characterize the phenotypic and genotypic spectrum of ATP1A3-related disorders in a Brazilian cohort. Methods We conducted a multicenter, cross-sectional study of individuals with ATP1A3 variants. Cases were recruited across reference centers in 9 Brazilian states, with standardized extraction of demographic, genetic, neuroimaging, EEG, ECG, and clinical data. Variants were annotated using transcript NM_152296.5 (hg19). AlphaFold was used for structural visualization. Multiple correspondence analysis (MCA) was performed to explore symptom clustering. This study was approved by the Ethics Committee of Federal University of São Paulo (Approval No.: 82533124.0.0000.5505). Results A total of 41 patients with ATP1A3 variants were included. Seven phenotypic categories were represented: AHC (17/41), RDP (10/41), CAPOS (7/41), relapsing encephalopathy with cerebellar ataxia (RECA; 4/41), fever-induced paroxysmal weakness and encephalopathy (FIPWE; 1/41), developmental and epileptic encephalopathy 99 (DEE99; 1/41), and malformation of cortical development (MCD; 1/41). Two neonatal-onset cases (DEE99 and MCD) were fatal. We identified 22 distinct ATP1A3 variants, including 4 novel variants (p.Gln920His, p.Arg827Gly, p.Glu670Ala, and c.606+5G>T). Clinical overlap was substantial: Cognitive impairment and seizures occurred across all phenotypes; hypotonia was present in 6 of 7 main phenotypes; abnormal eye movements and fever-induced symptoms occurred in all except MCD; and paroxysmal symptoms were reported in all, except DEE99. MCA demonstrated no discrete clustering by classical phenotype, reinforcing the continuous nature of the ATP1A3 spectrum. ECG abnormalities were rare in our cohort (1/20). Discussion Our findings expand the clinical and genetic landscape of ATP1A3-related disorders and underscore major phenotypic overlap among classical syndromes. The results highlight the need for a unified diagnostic framework. This study also demonstrates the feasibility and scientific value of coordinated rare disease research in resource-limited settings.
Victor Rebelo Procaci, Raphael Pinheiro Camurugy da Hora, Anna Maria Gomes et al.· Neurology: Genetics· 0 citations
Heterozygous pathogenic variants in the
KCNQ2
gene underlie a broad phenotypic spectrum ranging from self-limited (familial) neonatal epilepsy (SeLNE) to developmental and epileptic encephalopathy or isolated intellectual disability. The
KCNQ2
gene encodes subunits of a voltage-gated potassium channel involved in neuronal excitability, and its mutations are known to have both loss-of-function (LoF) and gain-of-function (GoF) effects, resulting in distinct neurological syndromes. The recurrent missense LoF variant
KCNQ2
p.(Arg214Trp) has been previously reported in a single family with a presumed SeLNE phenotype, without detailed adult follow-up and with additional database-reported evidence suggesting a broader phenotype associated with this recurrent variant.
Here, we report a family with two adult carriers of the heterozygous
KCNQ2
p.(Arg214Trp) variant identified through whole-exome sequencing, including long-term follow-up into late adulthood. In addition, a literature review of previously reported cases carrying the same recurrent variant was performed.
Both individuals presented with early-onset focal epilepsy with a relapsing course, characterized by prolonged seizure-free periods followed by recurrence in adulthood. The proband demonstrated transient motor regression, developmental delay, moderate intellectual disability, ataxia and fine motor impairment. The father exhibited milder cognitive impairment and additional comorbidities in later life.
These findings challenge the concept of
KCNQ2
p.(Arg214Trp) as a self-limited epilepsy-associated variant and indicate a broader phenotypic spectrum, with persistence of epilepsy and associated neurological and non-neurological comorbidities into adulthood. Our report provides new insights into adult outcomes, aiding in genetic counseling and the long-term management of affected individuals. More extensive studies with larger cohorts carrying this variant are necessary to better define the full phenotypic spectrum and to distinguish comorbidities associated with different etiological factors, including perinatal factors.
P. Christova, M. Ostrožovičová, J. Neupauerová et al.· BMC Neurology· 0 citations