KCNQ2 mutations in childhood nonlesional epilepsy: Variable phenotypes and a novel mutation in a case series

Clinical and genetic analysis of 23 Chinese children with epilepsy associated with KCNQ2 gene mutations

OBJECTIVE

To summarize the clinical features and genetic mutation characteristics of Chinese children with KCNQ2-related epilepsy.

METHODS

A cohort of children with genetically caused epilepsy was evaluated at Linyi People's Hospital from January 2017 to December 2023. After next-generation sequencing and pathogenicity analysis, we summarized the medical records and genetic testing data of the children who had KCNQ2 gene mutations.

RESULTS

We identified 23 KCNQ2 gene mutations. 73.9% (n = 17) of the mutation sites were located in S5-S6 segments and the C-terminal region. In addition to the common phenotypes, 2 new phenotypes were identified: infantile convulsion with paroxysmal choreoathetosis (ICCA) and febrile seizure plus (FS+). Of all the cases with abnormal video-electro-encephalography, three cases with self-limited familial infantile epilepsy (SeLNE) exhibited a small number of multifocal discharges. Of the patients who have taken a particular antiepileptic drug, the statistics on the number of patients who have responded to the drug are as follows: oxcarbazepine (8/9, 88.9%), levetiracetam (5/7, 71.4%), phenobarbital (9/16, 56.3%), and topiramate (2/5, 40.0%). However, the efficacy of phenobarbital varied widely in treating SeLNE and KCNQ2-DEE. At the final follow-up, 1 case with SeLNE had a transient developmental regression and 7 cases with KCNQ2-DEE had mild to severe developmental backwardness.

SIGNIFICANCE

Although clinically rare, we report 10 new KCNQ2 mutations and two new phenotypes: ICCA and FS+. This further expands genetic and phenotypic spectrum of KCNQ2-related epilepsy. The gene mutation sites are mostly located in S5-S6 segments and the C-terminal region, and the former is usually associated with KCNQ2-DEE. Sodium channel blockers (including oxcarbazepine and topiramate) and levetiracetam should be prioritized over phenobarbital for KCNQ2-DEE. Some cases with KCNQ2-related epilepsy may have transient developmental regression during periods of frequent seizures. Early treatment and early seizure control may be beneficial for willing outcomes in children with KCNQ2-DEE.

PLAIN LANGUAGE SUMMARY

This article reports 23 cases of children with KCNQ2-related epilepsy, including 10 new mutation sites and 2 new phenotypes. It further expands the genetic and phenotypic spectrum of KCNQ2-related epilepsy. In addition, the article summarizes the gene mutation characteristics and clinical manifestations of children with KCNQ2-related epilepsy, with the expectation of providing a certain theoretical basis for the diagnosis and treatment of such patients.

A novel de novo heterozygous variant of the KCNQ2 gene: Contribution to early‑onset epileptic encephalopathy in a female infant

Early-onset epileptic encephalopathy (EOEE) represents one of the most severe epilepsies, characterized by recurrent seizures during early infancy, electroencephalogram (EEG) abnormalities and varying degrees of neurodevelopmental delay. The KCNQ2 gene has been reported to have a major role in EOEE. In the present study, a 3-month-old female infant from the Chinese Lisu minority with EOEE was analyzed. Detailed clinical evaluations and next-generation sequencing were performed to investigate the clinical and genetic characteristics of this patient, respectively. Furthermore, the three-dimensional structure of the mutant protein was predicted by SWISS-Model and the expression of KCNQ2 protein in the patient was assessed by flow cytometry. It was observed that the patient presented with typical clinical features of EOEE, including repeated non-febrile seizures and significant EEG abnormalities. A novel heterozygous missense variant c.431G>C (p.R144P) in KCNQ2 was identified in the patient and the genotyping of KCNQ2 in the patient's parents suggested that this variant was de novo. Subsequently, the breakage of hydrogen bonds between certain amino acids was predicted by structural analysis of the mutant protein. Flow cytometric analysis detected a significant reduction buts not complete loss of native KCNQ2 protein expression in the patient (25.1%). In conclusion, a novel variant in KCNQ2 was confirmed as the genetic cause for EOEE in this patient. The present study expanded the pathogenic mutation spectrum of KCNQ2, enhanced the understanding of the molecular pathogenesis of EOEE and provided novel clues for research on the genotype-phenotype correlation in this disease.

Behavior of KCNQ Channels in Neural Plasticity and Motor Disorders

The broad distribution of voltage-gated potassium channels (VGKCs) in the human body makes them a critical component for the study of physiological and pathological function. Within the KCNQ family of VGKCs, these aqueous conduits serve an array of critical roles in homeostasis, especially in neural tissue. Moreover, the greater emphasis on genomic identification in the past century has led to a growth in literature on the role of the ion channels in pathological disease as well. Despite this, there is a need to consolidate the updated findings regarding both the pharmacotherapeutic and pathological roles of KCNQ channels, especially regarding neural plasticity and motor disorders which have the largest body of literature on this channel. Specifically, KCNQ channels serve a remarkable role in modulating the synaptic efficiency required to create appropriate plasticity in the brain. This role can serve as a foundation for clinical approaches to chronic pain. Additionally, KCNQ channels in motor disorders have been utilized as a direction for contemporary pharmacotherapeutic developments due to the muscarinic properties of this channel. The aim of this study is to provide a contemporary review of the behavior of these channels in neural plasticity and motor disorders. Upon review, the behavior of these channels is largely dependent on the physiological role that KCNQ modulatory factors (i.e., pharmacotherapeutic options) serve in pathological diseases.

KCNQ2-Related Neonatal Epilepsy Treated With Vitamin B6: A Report of Two Cases and Literature Review

Potassium Voltage-Gated Channel Subfamily Q Member 2 (KCNQ2) gene has been initially associated with "Benign familial neonatal epilepsy" (BFNE). Amounting evidence arising by next-generation sequencing techniques have led to the definition of new phenotypes, such as neonatal epileptic encephalopathy (NEE), expanding the spectrum of KCNQ2-related epilepsies. Pyridoxine (PN) dependent epilepsies (PDE) are a heterogeneous group of autosomal recessive disorders associated with neonatal-onset seizures responsive to treatment with vitamin B6 (VitB6). Few cases of neonatal seizures due to KCNQ2 pathogenic variants have been reported as successfully responding to VitB6. We reported two cases of KCNQ2-related neonatal epilepsies involving a 5-year-old male with a paternally inherited heterozygous mutation (c.1639C>T; p.Arg547Trp), and a 10-year-old female with a de novo heterozygous mutation (c.740C>T; p.Ser247Leu). Both children benefited from VitB6 treatment. Although the mechanisms explaining the efficacy of VitB6 in such patients remain unclear, this treatment option in neonatal-onset seizures is easily taken into account in Neonatal Intensive Care Units (NICUs). Further studies should be conducted to better define clinical guidelines and treatment protocols.

Posttranslational modifications & lithium's therapeutic effect-Potential biomarkers for clinical responses in psychiatric & neurodegenerative disorders

Several neurodegenerative diseases and neuropsychiatric disorders display aberrant posttranslational modifications (PTMs) of one, or many, proteins. Lithium treatment has been used for mood stabilization for many decades, and is highly effective for large subsets of patients with diverse neurological conditions. However, the differential effectiveness and mode of action are not fully understood. In recent years, studies have shown that lithium alters several protein PTMs, altering their function, and consequently neuronal physiology. The impetus for this review is to outline the links between lithium's therapeutic mode of action and PTM homeostasis. We first provide an overview of the principal PTMs affected by lithium. We then describe several neuropsychiatric disorders in which PTMs have been implicated as pathogenic. For each of these conditions, we discuss lithium's clinical use and explore the putative mechanism of how it restores PTM homeostasis, and thereby cellular physiology. Evidence suggests that determining specific PTM patterns could be a promising strategy to develop biomarkers for disease and lithium responsiveness.

In Silico Predictions of KCNQ Variant Pathogenicity in Epilepsy

BACKGROUND

Variants in KCNQ2 and KCNQ3 may cause benign neonatal familial seizures and early infantile epileptic encephalopathy. Previous reports suggest that in silico models cannot predict pathogenicity accurately enough for clinical use. Here we sought to establish a model to accurately predict the pathogenicity of KCNQ2 and KCNQ3 missense variants based on available in silico prediction models.

METHODS

ClinVar and gnomAD databases of reported KCNQ2 and KCNQ3 missense variants in patients with neonatal epilepsy were accessed and classified as benign, pathogenic, or of uncertain significance. Sensitivity, specificity, and classification accuracy for prediction of pathogenicity were determined and compared for 10 widely used prediction algorithms program. A mathematical model of the variants (KCNQ Index) was created using their amino acid location and prediction algorithm scores to improve prediction accuracy.

RESULTS

Using clinically characterized variants, the free online tool PROVEAN accurately predicted pathogenicity 92% of the time and the KCNQ Index had an accuracy of 96%. However, when including the gnomAD database as benign variants, only the KCNQ Index was able to predict pathogenicity with an accuracy greater than 90% (sensitivity = 93% and specificity = 98%). No model could accurately predict the phenotype of variants.

CONCLUSION

We show that KCNQ channel variant pathogenicity can be predicted by a novel KCNQ Index in neonatal epilepsy. However, more work is needed to accurately predict the patient's epilepsy phenotype from in silico algorithms.

Adult phenotype of KCNQ2 encephalopathy

BACKGROUND

Pathogenic KCNQ2 variants are a frequent cause of developmental and epileptic encephalopathy.

METHODS

We recruited 13 adults (between 18 years and 45 years of age) with KCNQ2 encephalopathy and reviewed their clinical, EEG, neuroimaging and treatment history.

RESULTS

While most patients had daily seizures at seizure onset, seizure frequency declined or remitted during childhood and adulthood. The most common seizure type was tonic seizures (early) infancy, and tonic-clonic and focal impaired awareness seizures later in life. Ten individuals (77%) were seizure-free at last follow-up. In 38% of the individuals, earlier periods of seizure freedom lasting a minimum of 2 years followed by seizure recurrence had occurred. Of the 10 seizure-free patients, 4 were receiving a single antiseizure medication (ASM, carbamazepine, lamotrigine or levetiracetam), and 2 had stopped taking ASM. Intellectual disability (ID) ranged from mild to profound, with the majority (54%) of individuals in the severe category. At last contact, six individuals (46%) remained unable to walk independently, six (46%) had limb spasticity and four (31%) tetraparesis/tetraplegia. Six (46%) remained non-verbal, 10 (77%) had autistic features/autism, 4 (31%) exhibited aggressive behaviour and 4 (31%) destructive behaviour with self-injury. Four patients had visual problems, thought to be related to prematurity in one. Sleep problems were seen in six (46%) individuals.

CONCLUSION

Seizure frequency declines over the years and most patients are seizure-free in adulthood. Longer seizure-free periods followed by seizure recurrence are common during childhood and adolescence. Most adult patients have severe ID. Motor, language and behavioural problems are an issue of continuous concern.

Capturing seizures in clinical trials of antiseizure medications for KCNQ2-DEE

Literature review of patients with KCNQ2 developmental and epileptic encephalopathy (KCNQ2-DEE) reveals, based on 16 reports including 139 patients, a clinical phenotype that includes age- and disease-specific stereotyped seizures. The typical seizure type of KCNQ2-DEE, focal tonic, starts within 0-5 days of life and is readily captured by video-electroencephalography VEEG for clinical and genetic diagnosis. After initial identification, KCNQ2-DEE seizures are clinically apparent and can be clearly identified without the use of EEG or VEEG. Therefore, we propose that the 2019 recommendations from the International League against Epilepsy (ILAE), the Pediatric Epilepsy Research Consortium (PERC), for capturing and recording seizures for clinical trials (Epilepsia Open, 4, 2019, 537) are suitable for use in KCNQ2-DEE‒associated antiseizure medicine (ASM) treatment trials. The ILAE/PERC consensus guidance states that a caregiver-maintained seizure diary, completed by caregivers who are trained to recognize seizures using within-patient historical recordings, accurately captures seizures prospectively in a clinical trial. An alternative approach historically endorsed by the Food and Drug Administration (FDA) compares seizure counts captured on VEEG before and after treatment. A major advantage of the ILAE/PERC strategy is that it expands the numbers of eligible patients who meet inclusion criteria of clinical trials while maintaining accurate seizure counts (Epilepsia Open, 4, 2019, 537). Three recent phase 3 pivotal pediatric trials investigating ASMs to treat syndromic seizures in patients as young as 2 years of age (N Engl J Med, 17, 2017, 699; Lancet, 21, 2020, 2243; Lancet, 17, 2018, 1085); and ongoing phase 2 open-label pediatric clinical trial that includes pediatric epileptic syndromes as young as 1 month of age (Am J Med Genet A, 176, 2018, 773), have already used caregiver-maintained seizure diaries successfully. For determining the outcome of a KCNQ2-DEE ASM treatment trial, the use of a seizure diary to count seizures by trained observers is feasible because the seizures of KCNQ2-DEE are clinically apparent. This strategy is supported by successful precedent in clinical trials in similar age groups and has the endorsement of the international pediatric epilepsy community.

Schizophrenic Psychosis Symptoms in a Background of Mild-To-Moderate Carnitine Palmitoyltransferase II Deficiency: A Case Report

Schizophrenia is a multifaceted mental illness characterized by cognitive and neurobehavioral abnormalities. Carnitine palmitoyltransferase II (CPT II) deficiency is a metabolic disorder resulting in impaired transport of long-chain fatty acids from the cytosol to the mitochondrial inner membrane, where fatty acid β-oxidation takes place. Here, we present an interesting clinical case of an adolescent male that presented with psychosis and a history of mild-to-moderate CPT II deficiency. To identify germline genetic variation that may contribute to the phenotypes observed, we performed whole-exome sequencing on DNA from the proband, unaffected fraternal twin, and biological parents. The proband was identified to be homozygous for the p.Val368Ile and heterozygous for the p.Met647Val variant in CPT2. Each of these variants are benign on their own; however, their combined effect is unclear. Further, variation was identified in the dopamine β-hydroxylase (DBH) gene (c.339+2T>C), which may contribute to decreased activity of DBH; however, based on the patient’s presentation, severe DBH deficiency is unlikely. In conclusion, the variants identified in this study do not clearly explain the observed patient phenotypes, indicating that the complex phenotypes are likely caused by an interplay of genetic and environmental factors that warrant further investigation.

Ictal and interictal electroencephalographic findings can contribute to early diagnosis and prompt treatment in KCNQ2-associated epileptic encephalopathy

BACKGROUND

KCNQ2-associated epilepsy is most common in neonatal genetic epilepsy. A prompt diagnosis to initialize early treatment is important.

METHODS

We studied the electroencephalographic (EEG) changes including automated EEGs and conventional EEGs monitoring of 10 nonconsanguineous cases with KCNQ2 mutations, identified among 162 (6%) childhood epilepsy. We compared 11 (25%) non-KCNQ2 seizures videoed from 44 automated EEG and EEG monitoring.

RESULTS

Patients with KCNQ2 seizures had received more antiepileptic treatments than patients in non-KCNQ2 group. Seizures were detected in all patients with KCNQ2 epileptic encephalopathy (EE); the detection rate in KCNQ2 group was more than in patients with non-KCNQ2. The ictal recordings showed 3 newborns presented with initial lower amplitudes (<15 μV) and fast activity (>20 Hz), evolving into higher-amplitude theta-delta waves. Two patient's ictal seizures showed recurrent focal tonic movements of the unilateral limbs associated with slowly continuous spikes in the contralateral hemisphere. The interictal EEGs in 5 KCNQ2 EE were burst-suppression. In 5 patients with familial KCNQ2 mutations, the interictal EEGs showed focal paroxysmal activity. Compared with 11 non-KCNQ2 EEG of ictal seizures, the differences are ictal EEGs initially appeared manifesting theta-delta waves without fast activities. In KCNQ2 seizures, patients with mutations locating in the selectivity filter controlling K⁺ permeability had severe EEG patterns and poor neurodevelopmental outcomes.

CONCLUSION

Ictal EEGs in KCNQ2 seizures are unique and different from the EEGs of seizures with other etiologies. An EEG monitoring can be a valuable tool for early diagnosing KCNQ2-associated seizures and for supporting prompt treatments.

Novel Dominant KCNQ2 Exon 7 Partial In-Frame Duplication in a Complex Epileptic and Neurodevelopmental Delay Syndrome

Complex neurodevelopmental syndromes frequently have an unknown etiology, in which genetic factors play a pathogenic role. This study utilizes whole-exome sequencing (WES) to examine four members of a family with a son presenting, since birth, with epileptic-like crises, combined with cerebral palsy, severe neuromotor and developmental delay, dystonic tetraparexia, axonal motor affectation, and hyper-excitability of unknown origin. The WES study detected within the patient a de novo heterozygous in-frame duplication of thirty-six nucleotides within exon 7 of the human KCNQ2 gene. This insertion duplicates the first twelve amino acids of the calmodulin binding site I. Molecular dynamics simulations of this KCNQ2 peptide duplication, modelled on the 3D structure of the KCNQ2 protein, suggest that the duplication may lead to the dysregulation of calcium inhibition of this protein function.

KCNQ2 mutations in childhood nonlesional epilepsy: Variable phenotypes and a novel mutation in a case series

BACKGROUND

Epilepsy caused by a KCNQ2 gene mutation usually manifests as neonatal seizures during the first week of life. The genotypes and phenotypes of KCNQ2 mutations are noteworthy.

METHODS

The KCNQ2 sequencings done were selected from 131 nonconsanguineous pediatric epileptic patients (age range: 2 days to 18 years) with nonlesional epilepsy.

RESULTS

Seven (5%) index patients had verified KCNQ2 mutations: c.387+1 G>T (splicing), c.1741 C>T (p.Arg581*), c.740 C>T p.(Ser247Leu), c.853 C>A p.(Pro285Thr), c.860 C>T p.(Thr287Ile), c.1294 C>T p.(Arg432Cys), and c.1627 G>A p.(Val543Met). We found, after their paternity had been confirmed, that three patients had de novo p.(Ser247Leu), p.(Pro285Thr), and p.(Thr287Ile) mutations and neonatal-onset epileptic encephalopathy; however, their frequent seizures remitted after they turned 6 months old. Those with the c.387+1G>T (splicing), (p.Arg581*), and p.(Val543Met) mutations presented with benign familial neonatal convulsions. In addition to their relatives, 14 patients had documented KCNQ2 mutations, and 12 (86%) had neonatal seizures. The seizures of all five patients treated with oxcarbazepine remitted.

CONCLUSION

KCNQ2-related epilepsy led to varied outcomes (from benign to severe) in our patients. KCNQ2 mutations accounted for 13% of patients with seizure onset before 2 months old in our study. KCNQ2 mutations can cause different phenotypes in children. p.(Pro 285Thr) is a novel mutation, and the p.(Pro 285Thr), p.(Ser247Leu), and p.(Thr287Ile) variants can cause neonatal-onset epileptic encephalopathy.

A Case of Neonatal Seizures With an Unusual Electroclinical Pattern

Benign familial neonatal epilepsy is a syndrome characterized by recurrent seizures occurring in the neonatal period. Seizures commonly begin at day 3 of life and usually abate by 1 to 4 months of life. Seizures are usually described as tonic with an asymmetric component with associated autonomic features. The authors report a newborn presenting with an unusual electroclinical phenotype. The electroencephalogram demonstrated an unusual pattern of electrical attenuation at the onset of seizures. Identification of these features is important for early recognition of this neonatal syndrome, as well as initiation of proper therapy.