HCN channels are activated by hyperpolarization, and help to control neuronal excitability. Marini et al. describe how de novo or inherited missense variants leading to loss- or gain-of-function of ...HCN1 are associated with a wide range of seizure disorders ranging from lethal neonatal epilepsy to benign generalized epilepsy.
Abstract
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels control neuronal excitability and their dysfunction has been linked to epileptogenesis but few individuals with neurological disorders related to variants altering HCN channels have been reported so far. In 2014, we described five individuals with epileptic encephalopathy due to de novo HCN1 variants. To delineate HCN1-related disorders and investigate genotype-phenotype correlations further, we assembled a cohort of 33 unpublished patients with novel pathogenic or likely pathogenic variants: 19 probands carrying 14 different de novo mutations and four families with dominantly inherited variants segregating with epilepsy in 14 individuals, but not penetrant in six additional individuals. Sporadic patients had epilepsy with median onset at age 7 months and in 36% the first seizure occurred during a febrile illness. Overall, considering familial and sporadic patients, the predominant phenotypes were mild, including genetic generalized epilepsies and genetic epilepsy with febrile seizures plus (GEFS+) spectrum. About 20% manifested neonatal/infantile onset otherwise unclassified epileptic encephalopathy. The study also included eight patients with variants of unknown significance: one adopted patient had two HCN1 variants, four probands had intellectual disability without seizures, and three individuals had missense variants inherited from an asymptomatic parent. Of the 18 novel pathogenic missense variants identified, 12 were associated with severe phenotypes and clustered within or close to transmembrane domains, while variants segregating with milder phenotypes were located outside transmembrane domains, in the intracellular N- and C-terminal parts of the channel. Five recurrent variants were associated with similar phenotypes. Using whole-cell patch-clamp, we showed that the impact of 12 selected variants ranged from complete loss-of-function to significant shifts in activation kinetics and/or voltage dependence. Functional analysis of three different substitutions altering Gly391 revealed that these variants had different consequences on channel biophysical properties. The Gly391Asp variant, associated with the most severe, neonatal phenotype, also had the most severe impact on channel function. Molecular dynamics simulation on channel structure showed that homotetramers were not conducting ions because the permeation path was blocked by cation(s) strongly complexed to the Asp residue, whereas heterotetramers showed an instantaneous current component possibly linked to deformation of the channel pore. In conclusion, our results considerably expand the clinical spectrum related to HCN1 variants to include common generalized epilepsy phenotypes and further illustrate how HCN1 has a pivotal function in brain development and control of neuronal excitability.
Objective
Autosomal recessive pathogenic variants of the SLC13A5 gene are associated with severe neonatal epilepsy, developmental delay, and tooth hypoplasia/hypodontia. We report on 14 additional ...patients and compare their phenotypic features to previously published patients to identify the clinical hallmarks of this disorder.
Methods
We collected clinical features of 14 patients carrying biallelic variants in SLC13A5 and performed a PubMed search to identify previously published patients.
Results
All patients presented clonic or tonic seizures in the first days of life, evolving into status epilepticus in 57%. Analysis of seizure frequency and developmental milestones divided into five epochs showed an evolutionary trajectory of both items. In the first 3 years of life, 72% of patients had weekly/monthly seizures, often triggered by fever; 14% were seizure‐free. Between the ages of 3 and 12 years, 60% become seizure‐free; in the following years, up to age 18 years, 57% were seizure‐free. After the age of 18 years, all three patients reaching this age were seizure‐free. Similarly, 86% of patients at onset presented mild to moderate developmental impairment and diffuse hypotonia. In late childhood, all had developmental delay that was severe in most. Benzodiazepines, phenobarbital, phenytoin, and carbamazepine were the most effective drugs. Eight probands carried heterozygous compound variants, and homozygous pathogenic variants occurred in six. Literature review identified 45 patients carrying SLC13A5 gene pathogenic variants whose clinical features overlapped with our cohort. A peculiar and distinguishing sign is the presence of tooth hypoplasia and/or hypodontia in most patients.
Significance
Autosomal recessive pathogenic variants in SLC13A5 are associated with a distinct neonatal epileptic encephalopathy evolving into severe cognitive and motor impairment, yet with seizures that settle down in late childhood. Tooth hypoplasia or hypodontia remains the peculiar feature. The SLC13A5 gene should be screened in neonatal epileptic encephalopathies; its recessive inheritance has relevance for genetic counseling.
This retrospective study assessed long‐term effectiveness of add‐on perampanel (PER) in patients with Lennox–Gastaut syndrome (LGS). Outcomes included time to PER failure and time to seizure relapse ...in responders. PER failure was defined as either discontinuation of PER or initiation of another treatment. Seizure relapse in responders was defined as occurrence of a seizure in seizure‐free patients and increase of at least 50% in average monthly seizure frequency for those who were responders. Eighty‐seven patients were included. Treatment failure occurred in 52 (59.8%) subjects at a median time of 12 months. Treatment failure was due to lack of efficacy in 27 (52.0%) patients, lack of tolerability in 14 (27.0%), and both reasons in 11 (21.0%). A slower titration was associated with a lower risk of PER failure compared to faster titration schedules, and the occurrence of adverse events increased the risk of treatment failure. Thirty‐six patients (41.4%) were responders during a median follow‐up of 11 months. Seizure relapse occurred in 13 of 36 (36.1%) patients after a median time of 21 months. The overall rate of seizure responders was 23 of 87 (26.4%) at the end of follow‐up. This study provides real‐world evidence on the effectiveness of PER as adjunctive treatment in LGS patients.
Background
Lafora disease (LD) is a neurodegenerative disorder featuring action and stimulus-sensitive myoclonus, epilepsy, and cognitive deterioration. Mutations in the
EPM2A/EPM2B
genes classically ...prove causative for the disease in most cases. Since full-field electroretinogram (ffERG) may reveal early-stage changes in a wide spectrum of diseases, we aimed to evaluate retinal cones and rods dysfunction in a cohort of Italian LD patients.
Methods
Patients with genetically confirmed LD were recruited and subjected to ffERG analysis following the International Society for Clinical Electrophysiology of Vision (ISCEV) protocol.
Results
Six patients aged between 13 and 26 years (mean 19.5 years) were included. The mean age at disease onset was 12.5 years with a mean disease duration of 7 years. The ffERG analysis revealed a global mild to severe generalized cones dysfunction in all patients. Linear correlation was identified between disease stage and the degree of cones and rods dysfunction, as well as between the type of mutation and the cones and rods dysfunction.
Conclusions
This study brings further evidence of early retinal alterations in LD patients. The cones and rods dysfunction grade is related to disease duration. The ffERG is an important tool to determine the disease stage, allowing to evaluate either natural or treatment-related disease progression in a minimally invasive way.
•Catatonia is a red flag for autoimmune conditions, even without biological evidence.•Patients with suspected AE had a good response to treatment and low relapses rate.•Autoimmune catatonia can be a ...severity/morbidity marker regarding outcomes.•Autoimmune catatonia require both early and aggressive immunosuppressive treatments.
Patients with autoimmune encephalitis (AE) are likely to exhibit an acute onset of severe psychiatric features, including psychosis and/or catatonia. Based on the high prevalence of catatonia in AE and our clinical experience, we hypothesized that catatonia might be a marker of severity requiring more aggressive treatment approaches.
To reach a sufficient number of cases with brain-autoimmune conditions, we pooled two samples (N = 58): the first from the French National Network of Rare Psychiatric diseases and the second from the largest Italian neuro-pediatrics center for encephalopathies. Autoimmune conditions were diagnosed using a multidisciplinary approach and numerous paraclinical investigations. We retrospectively compared patients with and without catatonia for psychiatric and non-psychiatric clinical features, biological and imaging assessments, type of immunotherapy used and outcomes.
The sample included 25 patients (43%) with catatonia and 33 (57%) without catatonia. Forty-two patients (72.4%) had a definite AE (including 27 anti-NMDA receptor encephalitis) and 16 (27.6%) suspected autoimmune encephalitis. Patients with catatonia showed significantly more psychotic features 18 (72%) vs 9 (27.3%), p < 0.001) and more movement disorders 25 (100%) vs 20 (60.6%), p < 0.001 than patients without catatonia. First line (corticoids, immunoglobulin and plasma exchanges) and second line (e.g., rituximab) therapies were more effective in patients with catatonia, with 24 (96%) vs 22 (66.7%) (p = 0.006) and 17 (68%) vs 9 (27.3%) (p = 0.002), respectively. However, those with catatonia received more combinations of first and second line treatments and had more relapses during outcomes.
Despite its exploratory design, the study supports the idea that autoimmune catatonia may be a marker of severity and morbidity in terms of initial presentation and relapses, requiring the need for early and aggressive treatment.
Missense variants of hyperpolarization‐activated, cyclic nucleotide‐gated (HCN) ion channels cause variable phenotypes, ranging from mild generalized epilepsy to developmental and epileptic ...encephalopathy (DEE). Although variants of HCN1 are an established cause of DEE, those of HCN2 have been reported in generalized epilepsies. Here we describe the first case of DEE caused by the novel de novo heterozygous missense variant c.1379G>A (p.G460D) of HCN2. Functional characterization in transfected HEK293 cells and neonatal rat cortical neurons revealed that HCN2 p.G460D currents were strongly reduced compared to wild‐type, consistent with a dominant negative loss‐of‐function effect. Immunofluorescence staining showed that mutant channels are retained within the cell and do not reach the membrane. Moreover, mutant HCN2 also affect HCN1 channels, by reducing the Ih current expressed by the HCN1‐HCN2 heteromers. Due to the persistence of frequent seizures despite pharmacological polytherapy, the patient was treated with a ketogenic diet, with a significant and long‐lasting reduction of episodes. In vitro experiments conducted in a ketogenic environment demonstrated that the clinical improvement observed with this dietary regimen was not mediated by a direct action on HCN2 activity. These results expand the clinical spectrum related to HCN2 channelopathies, further broadening our understanding of the pathogenesis of DEE.
Glucose transporter type 1 deficiency syndrome (Glut1 DS) is a rare neurological disorder caused by impaired glucose delivery to the brain. The clinical spectrum of Glut1 DS mainly includes epilepsy, ...paroxysmal dyskinesia (PD), developmental delay and microcephaly. Glut1 DS diagnosis is based on the identification of hypoglycorrhachia and pathogenic mutations of the
SLC2A1
gene. Here, we report the molecular screening of
SLC2A1
in 354 patients clinically suspected for Glut1 DS. From this cohort, we selected 245 patients for whom comprehensive clinical and laboratory data were available. Among them, we identified 19 patients carrying nucleotide variants of pathological significance, 5 of which were novel. The symptoms of onset, which varied from neonatal to adult age, included epilepsy, PD or non-epileptic paroxysmal manifestations. The comparison of the clinical features between the 19
SLC2A1
mutated and the 226 non-mutated patients revealed that the onset of epilepsy within the first year of life (when associated with developmental delay or other neurological manifestations), the association of epilepsy with PD and acquired microcephaly are more common in mutated subjects. Taken together, these data confirm the variability of expression of the phenotypes associated with mutation of
SLC2A1
and provide useful clinical tools for the early identification of subjects highly suspected for the disease.
•Non-sense heterozygous compound mutations of the CNTNAP2 gene can cause Pitt-Hopkins-like syndrome with severe epileptic phenotype.•Pharmacoresistant focal epilepsy may be a trait of the ...syndrome•Stiripentol treatment led to prolonged and sustained control of seizures.
An increasing number of developmental and epileptic encephalopathies have been correlated with variants of ion channel genes, and in particular of potassium channels genes, such as KCNA1, KCNA2, ...KCNB1, KCNQ2, KCTD7 and KCNT1.
Here we report a child with an early severe developmental and epileptic encephalopathy, spastic tetraplegia, opisthotonos attacks. The whole exome sequencing showed the de novo heterozygous variant c.1411G > C (p.Val471Leu) in the KCNC2 gene.
Although this is, to our knowledge, the first case of encephalopathy associated with a KCNC2 gene variant, and further confirmatory studies are needed, previous preclinical and clinical evidence seems to suggest that KCNC2 is a new candidate epilepsy gene.
ABSTRACT
Mutations in the thyroid hormone transporter SLC16A2 (MCT8) cause the Allan–Herndon–Dudley Syndrome (AHDS), characterized by severe psychomotor retardation and peripheral thyrotoxicosis. ...Here, we report three newly identified AHDS patients. Previously documented mutations were identified in probands 1 (p.R271H) and 2 (p.G564R), resulting in a severe clinical phenotype. A novel mutation (p.G564E) was identified in proband 3, affecting the same Gly564 residue, but resulting in a relatively mild clinical phenotype. Functional analysis in transiently transfected COS‐1 and JEG‐3 cells showed a near‐complete inactivation of TH transport for p.G564R, whereas considerable cell‐type‐dependent residual transport activity was observed for p.G564E. Both mutants showed a strong decrease in protein expression levels, but differentially affected Vmax and Km values of T3 transport. Our findings illustrate that different mutations affecting the same residue may have a differential impact on SLC16A2 transporter function, which translates into differences in severity of the clinical phenotype.
Mutations in the thyroid hormone transporter SLC16A2 (MCT8) result in the Allan‐Herndon‐Dudley syndrome (AHDS), characterized by severe intellectual disability and abnormal serum thyroid hormone levels. Here, we report 3 newly identified AHDS patients, of whom 2 carry a different mutation affecting the same Gly564 residue (p.G564E and p.G564R). Interestingly, a striking difference in severity of the clinical phenotype was observed between these 2 patients, which corresponded to the residual transporter activity of both mutant transporters in our in vitro studies.
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