De novo STXBP1 mutations are among the most frequent causes of epilepsy and encephalopathy. Most patients have severe to profound ID with little correlation among seizure onset, seizure severity, and the degree of ID. Accordingly, we hypothesize that seizure severity and ID present 2 independent dimensions of the STXBP1-E phenotype. STXBP1-E may be conceptualized as a complex neurodevelopmental disorder rather than a primary epileptic encephalopathy.

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Recently, mutations in the tau gene on chromosome 17 were found causative for autosomal dominantly inherited frontotemporal dementia and parkinsonism (FTDP‐17). We describe a family carrying a missense mutation at nucleotide 1137 C → T, resulting in the amino acid substitution P301S. Methods of investigations include clinical, electrophysiological, and imaging techniques. This kindred presents with a novel phenotype characterized by an early onset of rapidly progressive frontotemporal dementia and parkinsonism in combination with epileptic seizures. We define the dopaminergic deficits as being predominantly presynaptic by the use of single‐photon emission computed tomography with a dopamine transporter ligand. The association of this early‐onset phenotype with P301S mutation is not entirely consistent with current criteria for the diagnosis of frontotemporal dementias and may encourage the search for tau mutations in diseases similar but not identical to FTDP‐17. Also, the change from proline to serine suggests that this mutation might contribute to tau hyperphosphorylation.

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Background: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 analyse 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 (EOAE), focal epilepsy (FE), and myoclonic-atonic epilepsy (MAE). 10/18 variants were de novo and 8/18 variants were classified as modifying variants. 8 drug responsive cases became seizure-free using valproic acid as monotherapy or in combination including severe DEE cases. Functional analysis of four variants demonstrated gain-of-function in three severely affected DEE cases and loss-of-function in one case with a milder phenotype (GGE) as the underlying pathomechanisms.Conclusion: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.

Temporal lobe epilepsy (TLE) is one of the syndromes linked to antibodies against glutamic acid decarboxylase (GAD). It has been questioned whether ‘limbic encephalitis with GAD antibodies’ is a meaningful diagnostic entity. The immunopathogenesis of GAD-TLE has remained enigmatic. Improvement of immunological treatability is an urgent clinical concern. We retrospectively assessed the clinical, MRI and CSF course as well as brain tissue of 15 adult patients with GAD-TLE who underwent temporal lobe surgery. Brain tissue was studied by means of immunohistochemistry, multiplex fluorescent microscopy and transcriptomic analysis for inflammatory mediators and neuronal degeneration. In 10 patients, there was a period of mediotemporal swelling and T2 signal increase; in nine cases this occurred within the first 6 years after symptom onset. This resulted in unilateral or bilateral hippocampal sclerosis (HS); three cases developed HS already within the first 2 years. All CSF studies done within the first year (n = 6) revealed intrathecal synthesis of immunoglobulin G. Temporal lobe surgeries were done after a median disease duration of 9 years (range 3 weeks to 60 years). Only two patients became seizure free. Brain parenchyma collected during surgery in the first 6 years revealed high numbers of plasma cells but no signs of antibody-mediated tissue damage. Even more dense was the infiltration by CD8 + cytotoxic T lymphocytes (CTLs) that were seen to locally proliferate. Further, a portion of these cells revealed an antigen-specific resident memory T cell phenotype. Finally, CTLs with cytotoxic granzyme B+ granules were also seen in microglial nodules and attached to neurons, suggesting a CTL-mediated destruction of these cells. With longer disease duration, the density of all lymphocytes decreased. Whole transcriptome analysis in early/active cases (but not in late/inactive stages) revealed ‘T cell immunity’ and ‘Regulation of immune processes’ as the largest overrepresented clusters. To a lesser extent, pathways associated with B cells and neuronal degeneration also showed increased representation. Surgically treated patients with GAD-TLE go through an early active inflammatory, ‘encephalitic’ stage (≤ 6 years) with CTL-mediated, antigen-driven neuronal loss and antibody-producing plasma cells but without signs of complement-mediated cell death. Subsequently, patients enter an apparently immunologically inactive or low-active stage with ongoing seizures, probably caused by the structural damage to the temporal lobe. ‘Limbic encephalitis’ with GAD antibodies should be subsumed under GAD-TLE. The early tissue-damage explains why immunotherapy does usually not lead to seizure-freedom.

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Background KCNC2 encodes a member of the shaw-related voltage-gated potassium channel family (KV3.2), which are important for sustained high-frequency firing and optimized energy efficiency of action potentials in the brain. Methods Individuals with KCNC2 variants detected by exome sequencing were selected for clinical, further genetic and functional analysis. The cases were referred through clinical and research collaborations in our study. Four de novo variants were examined electrophysiologically in Xenopus laevis oocytes. Results We identified novel KCNC2 variants in 27 patients with various forms of epilepsy. Functional analysis demonstrated gain-of-function in severe and loss-of-function in milder phenotypes as the underlying pathomechanisms with specific response to valproic acid. Conclusion These findings implicate KCNC2 as a novel causative gene for epilepsy emphasizing the critical role of KV3.2 in the regulation of brain excitability with an interesting genotype-phenotype correlation and a potential concept for precision medicine.