Loss-of-function variants in the KCNQ5 gene are associated with genetic generalized epilepsies (original) (raw)
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Human KCNQ5 de novo mutations underlie epilepsy and intellectual disability
Journal of Neurophysiology
Six novel de novo human KCNQ5 variants were identified from children with neurodevelopmental delay, intellectual disability, and/or epilepsy. Expression of these variants along with four previously reported KCNQ5 variants from a similar cohort revealed GOF potassium channels, negatively shifted in V50 of activation and/or delayed deactivation kinetics. GOF is extended to KCNQ5/3 heteromeric channels, making these the predominant channels affected in heterozygous de novo patients. Kcnq5 LOF mice exhibited seizures, consistent with in vivo pathogenicity.
American journal of human genetics, 2017
KCNQ5 is a highly conserved gene encoding an important channel for neuronal function; it is widely expressed in the brain and generates M-type current. Exome sequencing identified de novo heterozygous missense mutations in four probands with intellectual disability, abnormal neurological findings, and treatment-resistant epilepsy (in two of four). Comprehensive analysis of this potassium channel for the four variants expressed in frog oocytes revealed shifts in the voltage dependence of activation, including altered activation and deactivation kinetics. Specifically, both loss-of-function and gain-of-function KCNQ5 mutations, associated with increased excitability and decreased repolarization reserve, lead to pathophysiology.
Dominant-negative effects of KCNQ2 mutations are associated with epileptic encephalopathy
Annals of Neurology, 2014
Objective: Mutations in KCNQ2 and KCNQ3, encoding the voltage-gated potassium channels K V 7.2 and K V 7.3, are known to cause benign familial neonatal seizures mainly by haploinsufficiency. Here, we set out to determine the disease mechanism of 7 de novo missense KCNQ2 mutations that were recently described in patients with a severe epileptic encephalopathy including pharmacoresistant seizures and pronounced intellectual disability. Methods: Mutations were inserted into the KCNQ2 cDNA. Potassium currents were recorded using 2microelectrode voltage clamping, and surface expression was analyzed by a biotinylation assay in cRNA-injected Xenopus laevis oocytes. Results: We observed a clear loss of function for all mutations. Strikingly, 5 of 7 mutations exhibited a drastic dominant-negative effect on wild-type K V 7.2 or K V 7.3 subunits, either by globally reducing current amplitudes (3 pore mutations) or by a depolarizing shift of the activation curve (2 voltage sensor mutations) decreasing potassium currents at the subthreshold level at which these channels are known to critically influence neuronal firing. One mutation significantly reduced surface expression. Application of retigabine, a recently marketed K V 7 channel opener, partially reversed these effects for the majority of analyzed mutations. Interpretation: The development of severe epilepsy and cognitive decline in children carrying 5 of the 7 studied KCNQ2 mutations can be related to a dominant-negative reduction of the resulting potassium current at subthreshold membrane potentials. Other factors such as genetic modifiers have to be postulated for the remaining 2 mutations. Retigabine or similar drugs may be used as a personalized therapy for this severe disease. ANN NEUROL 2014;75:382-394 T he neuronal voltage-gated potassium channels K V 7.2 and K V 7.3, encoded by KCNQ2 and KCNQ3 genes, are mutated in benign familial neonatal seizures (BFNS), an autosomal dominant epilepsy syndrome characterized by brief seizures beginning in the first days of life and resolving spontaneously after weeks to months.
A novel KCNQ3 mutation in familial epilepsy with focal seizures and intellectual disability
Epilepsia, 2014
Mutations in the KCNQ2 gene encoding for voltage-gated potassium channel subunits have been found in patients affected with early onset epilepsies with wide phenotypic heterogeneity, ranging from benign familial neonatal seizures (BFNS) to epileptic encephalopathy with cognitive impairment, drug resistance, and characteristic electroencephalography (EEG) and neuroradiologic features. By contrast, only few KCNQ3 mutations have been rarely described, mostly in patients with typical BFNS. We report clinical, genetic, and functional data from a family in which early onset epilepsy and neurocognitive deficits segregated with a novel mutation in KCNQ3 (c.989G>T; p.R330L). Electrophysiological studies in mammalian cells revealed that incorporation of KCNQ3 R330L mutant subunits impaired channel function, suggesting a pathogenetic role for such mutation. The degree of functional impairment of channels incorporating KCNQ3 R330L subunits was larger than that of channels carrying another KCNQ3 mutation affecting the same codon but leading to a different amino acid substitution (p.R330C), previously identified in two families with typical BFNS. These data suggest that mutations in KCNQ3, similarly to KCNQ2, can be found in patients with more severe phenotypes including intellectual disability, and that the degree of the functional impairment caused by mutations at position 330 in KCNQ3 may contribute to clinical disease severity.
Homomeric Kv7.2 current suppression is a common feature in KCNQ2 epileptic encephalopathy
Epilepsia, 2018
To gain insight into the mechanisms underlying KCNQ2 encephalopathy by examining the electrophysiologic properties of mutant Kv7.2 channels in different multimeric configurations. Methods: We analyzed the genotype-phenotype relationship in 4 patients with KCNQ2 encephalopathy and performed electrophysiologic analysis of M-currents mediated by homomeric Kv7.2 or heteromeric Kv7.2/Kv7.3 channels. Results: Negligible or no current was recorded in cells expressing homomeric E130K, W270R, or G281R de novo mutants, and it was reduced by more than 90% for the L243F maternally inherited mutant. The E130K and G281R mutants presented a marked dominant-negative behavior, whereas the current density was partially reduced (L243F) or not affected (W270R) when coexpressed with wildtype Kv7.2 subunits. In contrast, the extent of Kv7.3 "rescue," which yields negligible currents on its own, followed the sequence E130K > L243F > W270R, whereas no rescue was observed with the G281R mutant. No significant effects on current density were observed when subunits were expressed in a 0.5:0.5:1.0 (Kv7.2:mutant:Kv7.3) DNA ratio to mimic the genetic balance. There was an increase in sensitivity to phosphatidylinositol 4,5-bisphosphate (PIP 2) depletion for W270R/Kv7.3, but no substantial differences were observed when the mutated subunits were coexpressed with Kv7.2 or both Kv7.2 and Kv7.3. Significance: There was a marked disparity of the impact of these mutations on Kv7.2 function, which varied on association with Kv7.2 or Kv7.3 subunits. Current density of homomeric channels was the most reliable property relating Kv7.2 function to encephalopathy, but other factors are required to explain the milder phenotype for some individuals carrying the maternally inherited L243F mutation. We hypothesize that the role of homomeric Kv7.2 channels for fine-tuning neuronal connections during development is critical for the severity of the KCNQ2 encephalopathy.
Neurobiology of Disease, 2015
Mutations in the KCNQ2 gene encoding the voltage-dependent potassium M channel Kv7.2 subunit cause either benign epilepsy or early onset epileptic encephalopathy (EOEE). It has been proposed that the disease severity rests on the inhibitory impact of mutations on M current density. Here, we have analyzed the phenotype of 7 patients carrying the p.A294V mutation located on the S6 segment of the Kv7.2 pore domain (Kv7.2 A294V). We investigated the functional and subcellular consequences of this mutation and compared it to another mutation (Kv7.2 A294G) associated with a benign epilepsy and affecting the same residue. We report that all the patients carrying the p.A294V mutation presented the clinical and EEG characteristics of EOEE. In CHO cells, the total expression of Kv7.2 A294V alone, assessed by western blotting, was only 20% compared to wild-type. No measurable current was recorded in CHO cells expressing Kv7.2 A294V channel alone. Although the total Kv7.2 A294V expression was rescued to wild-type levels in cells co-expressing the Kv7.3 subunit, the global current density was still reduced by 83% compared to wild-type heteromeric channel. In a configuration mimicking the patients' heterozygous genotype i.e., Kv7.2 A294V /Kv7.2/Kv7.3, the global current density was reduced by 30%. In contrast to Kv7.2 A294V , the current density of homomeric Kv7.2 A294G was not significantly changed compared to wild-type Kv7.2. However, the current density of Kv7.2 A294G /Kv7.2/Kv7.3 and Kv7.2 A294G /Kv7.3 channels were reduced by 30% and 50% respectively, compared to wild-type Kv7.2/Kv7.3. In neurons, the p.A294V mutation induced a mislocalization of heteromeric mutant channels to the somato-dendritic compartment, while the p.A294G mutation did not affect the localization of the heteromeric channels to the axon initial segment. We conclude that this Neurobiology of Disease 80 (2015) 80-92
Scientific Reports, 2020
Pediatric epilepsy caused by KCNQ2 mutations can manifest benign familial neonatal convulsions (BFNC) to neonatal-onset epileptic encephalopathy (EE). Patients might manifest mild to profound neurodevelopmental disabilities. We analysed c.853C > A (P285T) and three mutations that cause KCNQ2 protein changes in the 247 position: c.740C > T (S247L), c.740C > A (S247X), and c.740C > G (S247W). S247L, S247W, and P285T cause neonatal-onset EE and poor neurodevelopmental outcomes; S247X cause BFNC and normal outcome. We investigated the phenotypes correlated with human embryonic kidney 293 (HEK293) cell functional current changes. More cell-current changes and a worse conductance curve were present in the homomeric transfected S247X than in S247L, S247W, and P285T. But in the heteromeric channel, S247L, S247W and P285T had more current impairments than did S247X. The protein expressions of S247X were nonfunctional. The outcomes were most severe in S247L and S247W, and severity was correlated with heteromeric current. Current changes were more significant in cells with homomeric S247X, but currents were "rescued" after heteromeric transfection of KCNQ2 and KCNQ3. This was not the case in cells with S247L, S247W. Our findings support that homomeric current changes are common in KCNQ2 neonatal-onset EE and KCNQ2 BFNC; however, heteromeric functional current changes are correlated with long-term neurodevelopmental outcomes. KCNQ2 (OMIM 602235)-associated seizures usually occur during the first week after birth and can contribute to benign familial neonatal convulsions (BFNC), benign familial neonatal-infantile seizures (BFNIS), benign familial infantile seizures (BFIS) 1-5 , and neonatal-onset epileptic encephalopathy (EE) 6-8. Mutations in KCNQ2, a voltage-gated potassium channel gene at 20q13, are usually inherited in an autosomal-dominant manner in benign epileptic syndromes 1,2. Patients with BFNC usually have seizures with a predicted benign course and predicted good neurodevelopmental outcomes 1-3,9,10. On follow-up, about 30% of patients with inherited KCNQ2 mutations might have recurrent seizures beyond neonatal age 10. Most neonatal-onset EE, mutations are de novo, and patients present with severe seizures and grave neurological consequences. Seizures often remit as the patients become older, but the patients usually have intellectual developmental delays or autism 11,12. At present, however, outcomes cannot be accurately predicted. Functional KCNQ channels are homo-or heteromers of four subunits each containing 6 transmembrane domains (S1-S6), which include a voltage sensor in S1-S4 and S5-S6, and a loop between S5-S6 that builds the ion channel pore, a cytoplasmic N-terminal, and a long C-terminal region with complex functions exhibiting interactions between syntaxin, phosphatidylinositol 4,5-bisphosphate, ankyrin-G, Syn-1A, and A-kinase
Epilepsia, 2016
Mutations in the KCNQ2 gene encoding the voltage-gated potassium channel subunit Kv7.2 cause early onset epileptic encephalopathy (EOEE). Most mutations have been shown to induce a loss of function or to affect the subcellular distribution of Kv7 channels in neurons. Herein, we investigated functional consequences and subcellular distribution of the p.V175L mutation of Kv7.2 (Kv7.2 V175L) found in a patient presenting EOEE. We observed that the mutation produced a 25-40 mV hyperpolarizing shift of the conductance-voltage relationship of both the homomeric Kv7.2 V175L and heteromeric Kv7.2 V175L /Kv7.3 channels compared to wild-type channels and a 10 mV hyperpolarizing shift of Kv7.2 V175L /Kv7.2/Kv7.3 channels in a 1:1:2 ratio mimicking the patient situation. Mutant channels also displayed faster activation kinetics and an increased current density that was prevented by 1 lM linopirdine. The p.V175L mutation did not affect the protein expression of Kv7 channels and its localization at the axon initial segment. We conclude that p.V175L is a gain of function mutation. This confirms previous observations showing that mutations having opposite consequences on M channels can produce EOEE. These findings alert us that drugs aiming to increase Kv7 channel activity might have adverse effects in EOEE in the case of gain-of-function variants.
Nine patients with KCNQ2-related neonatal seizures and functional studies of two missense variants
Scientific Reports
Mutations in KCNQ2 encoding for voltage-gated K channel subunits underlying the neuronal M-current have been associated with infantile-onset epileptic disorders. The clinical spectrum ranges from self-limited neonatal seizures to epileptic encephalopathy and delayed development. Mutations in KCNQ2 could be either gain- or loss-of-function which require different therapeutic approaches. To better understand genotype–phenotype correlation, more reports of patients and their mutations with elucidated molecular mechanism are needed. We studied 104 patients with infantile-onset pharmacoresistant epilepsy who underwent exome or genome sequencing. Nine patients with neonatal-onset seizures from unrelated families were found to harbor pathogenic or likely pathogenic variants in the KCNQ2 gene. The p.(N258K) was recently reported, and p. (G279D) has never been previously reported. Functional effect of p.(N258K) and p.(G279D) has never been previously studied. The cellular localization study ...