KCNC2 mutations

Schwarz N, Seiffert S, Pendziwiat M, Rademacher AV, Brünger T, Hedrich UBS, Augustijn PB, Baier H, Bayat A, Bisulli F, Buono RJ, Bruria BZ, Doyle MG, Guerrini R, Heimer G, Iacomino M, Kearney H, Klein KM, Kousiappa I, Kunz WS, Lerche H, Licchetta L, Lohmann E, Minardi R, McDonald M, Montgomery S, Mulahasanovic L, Oegema R, Ortal B, Papacostas SS, Ragona F, Granata T, Reif PS, Rosenow F, Rothschild A, Scudieri P, Striano P, Tinuper P, Tanteles GA, Vetro A, Zahnert F, Goldberg EM, Zara F, Lal D, May P, Muhle H, Helbig I, Weber Y. Spectrum of Phenotypic, Genetic, and Functional Characteristics in Patients With Epilepsy With KCNC2 Pathogenic Variants. Neurology. 2022 May 17;98(20):e2046-e2059. doi: 10.1212/WNL.0000000000200660. Epub 2022 Mar 21. PMID: 35314505.

Abstract

Background and objectives: KCNC2 encodes Kv3.2, a member of the Shaw-related (Kv3) voltage-gated potassium channel subfamily, which is important for sustained high-frequency firing and optimized energy efficiency of action potentials in the brain. The objective of this study was to analyze the clinical phenotype, genetic background, and biophysical function of disease-associated Kv3.2 variants.

Methods: Individuals with KCNC2 variants detected by exome sequencing were selected for clinical, further genetic, and functional analysis. Cases were referred through clinical and research collaborations. Selected de novo variants were examined electrophysiologically in Xenopus laevis oocytes.

Results: We identified novel KCNC2 variants in 18 patients with various forms of epilepsy, including genetic generalized epilepsy (GGE), developmental and epileptic encephalopathy (DEE) including early-onset absence epilepsy, focal epilepsy, and myoclonic-atonic epilepsy. Of the 18 variants, 10 were de novo and 8 were classified as modifying variants. Eight drug-responsive patients became seizure-free using valproic acid as monotherapy or in combination, including severe DEE cases. Functional analysis of 4 variants demonstrated gain of function in 3 severely affected DEE cases and loss of function in 1 case with a milder phenotype (GGE) as the underlying pathomechanisms.

Discussion: These findings implicate KCNC2 as a novel causative gene for epilepsy and emphasize the critical role of KV3.2 in the regulation of brain excitability.

Rademacher A, Schwarz N, Seiffert S, Pendziwiat M, Rohr A, van Baalen A, Helbig I, Weber Y, Muhle H. Whole-Exome Sequencing in NF1-Related West Syndrome Leads to the Identification of KCNC2 as a Novel Candidate Gene for Epilepsy. Neuropediatrics. 2020 Oct;51(5):368-372. doi: 10.1055/s-0040-1710524. Epub 2020 May 11. PMID: 32392612.

Abstract

Patients with neurofibromatosis type 1 (NF1) have an increased risk for West syndrome (WS), but the underlying mechanisms linking NF1 and WS are unknown. In contrast to other neurocutaneous syndromes, intracerebral abnormalities explaining the course of infantile spasms (IS) are often absent and the seizure outcome is usually favorable. Several studies have investigated a potential genotype-phenotype correlation between NF1 and seizure susceptibility, but an association was not identified. Therefore, we identified three patients with NF1-related WS (NF1-WS) in a cohort of 51 NF1 patients and performed whole-exome sequencing (WES) to identify genetic modifiers. In two NF1 patients with WS and good seizure outcome, we did not identify variants in epilepsy-related genes. However, in a single patient with NF1-WS and transition to drug-resistant epilepsy, we identified a de novo variant in KCNC2 (c.G499T, p.D167Y) coding for Kv3.2 as a previously undescribed potassium channel to be correlated to epilepsy. Electrophysiological studies of the identified KCNC2 variant demonstrated both a strong loss-of-function effect for the current amplitude and a gain-of-function effect for the channel activation recommending a complex network effect. These results suggest that systematic genetic analysis for potentially secondary genetic etiologies in NF1 patients and severe epilepsy presentations should be done.

Rydzanicz M, Zwoliński P, Gasperowicz P, Pollak A, Kostrzewa G, Walczak A, Konarzewska M, Płoski R. A recurrent de novo variant supports KCNC2 involvement in the pathogenesis of developmental and epileptic encephalopathy. Am J Med Genet A. 2021 Nov;185(11):3384-3389. doi: 10.1002/ajmg.a.62455. Epub 2021 Aug 27. PMID: 34448338.

Abstract

Developmental and epileptic encephalopathies (DEE) are a heterogenous group of conditions characterized by the co-occurrence of epilepsy and intellectual/developmental disability. Despite several known DEE-related genes, including these encoding ion channels, still many cases remain without molecular diagnosis. Here, we present a 2-year-old girl with severe DEE in whom whole exome sequencing revealed de novo p.(Val471Leu) variant in the KCNC2 encoding Kv3.2, a voltage-gated potassium channel. To the best of our knowledge, this is the third DEE case due to KCNC2 mutation. Our clinical and molecular findings, particularly the recurrence of p.(Val471Leu) in patient with similar clinical phenotype, further support KCNC2 as a novel DEE-associated gene.