大田原症候群

To systematically summarize the clinical phenotypes, treatment responses, prognosis, and genetic characteristics of STXBP1-encephalopathy in Chinese pediatric patients, and to explore the clinical value of genetic testing in this disease. We retrospectively analyzed the clinical data, gene variant information, and treatment outcomes of 19 children with STXBP1-encephalopathy admitted to the Department of Pediatrics, Second Affiliated Hospital of Zhejiang University, between January 2020 and January 2024. Whole-exome sequencing was performed for genetic diagnosis, and Sanger sequencing was used to verify variants and confirm their parental origin. Pathogenicity of variants was classified according to the American College of Medical Genetics and Genomics guidelines. STXBP1-encephalopathy showed early onset, with 15 cases (78.9%) occurring within the 1st month of life. Five patients were diagnosed with Ohtahara syndrome, 5 with West syndrome, and 9 with unclassifiable early-onset epileptic encephalopathy. All patients had abnormal electro-encephalogram findings, mainly burst suppression (68.4%) and hypsarrhythmia (63.2%). Among the 19 patients, 1 achieved seizure freedom and discontinued antiepileptic drugs, and 4 achieved seizure control with levetiracetam. A total of 18 de novo pathogenic/likely pathogenic variants in STXBP1 were identified, including 7 novel variants: c.326-3(IVS5)delC, c.656del(p.Met219Argfs*13), c.746-747del(p.F249fs*6), c.798T > G(p.Y266*), c.1155delC(p.D385fs), c.1249G > A(p.G417S), and c.1250-2A > G. STXBP1 pathogenic variants are an important cause of early-onset developmental epileptic encephalopathy in Chinese children. Genetic testing is crucial for early diagnosis of STXBP1-encephalopathy. Levetiracetam shows good efficacy in controlling seizures in these patients, and early use is recommended. The 7 novel variants identified in this study expand the STXBP1 mutation spectrum.

Developmental and epileptic encephalopathy (DEE) is a severe neurological disorder. Biallelic mutations in the nuclear-encoded mitochondrial chaperone gene FOXRED1, a specific assembly factor for complex I, cause mitochondrial dysfunction; however, their role in DEE pathogenesis remains unexplored. Clinical data and peripheral blood mononuclear cells (PBMCs) were obtained from two patients with compound heterozygous FOXRED1 mutations (c.850T>C (p.C284R)/c.1054C>T (p.R352W) and c.1054C>T (p.R352W)/c.3dup (p.I2Dfs*35) and age-matched controls. Mitochondrial phenotyping, included complex I activity, mitochondrial respiration stress test, membrane potential, intracellular ROS, and NAD+/NADH ratio, were performed. Both patients exhibited early-onset refractory seizures, basal ganglia lesions, hyperlacticemia, and developmental regression. FOXRED1 mutations resulted in 50% reduction in complex I activity, dissasembly of complex I, mitochondrial depolarization, oxidative stress, and NAD+/NADH imbalance. Niacin restored the NAD+/NADH ratio in vitro, while clinical supplementation reduced blood lactate levels, suggesting it may be a potential therapeutic option.

Heterozygous de novo and inherited biallelic pathogenic variants in DNM1 have been reported in association with autosomal dominant (AD) and autosomal recessive (AR) developmental and epileptic encephalopathy, respectively, due to aberrant dynamin function or expression, with each inheritance pattern associated with a different mechanism of disease. We report an instance of DNM1-related early infantile developmental and epileptic encephalopathy due to compound heterozygous pathogenic variants with different functional effects: the de novo dominant negative-associated c.194C>A (p.Thr65Asn), and the maternally inherited loss of function-associated c.850C>T (p.Gln284*). We describe this patient's severe clinical presentation and disease progression as compared to those previously reported with either AD or AR DNM1-related disease. We hypothesize about the interactions and outcomes of the two variants at the molecular level following review of in vitro and in vivo functional data and demonstrate the utility of long-read genome sequencing for phasing the variants and confirming this individual's molecular diagnosis.

According to the World Health Organization, more than 50 million people worldwide have epilepsy, and about 5 million new cases are reported annually. According to other data, the number of patients exceeds 70.000.000, highlighting the relevance of this condition. Studies of developmental epileptic encephalopathies leading to early disability are particularly relevant. About 900 gene mutations associated with different types of epilepsy have been identified so far. One of the prominent «channelopathy genes» representatives is KCNT1, coding the largest subunit of the sodium-activated potassium channel, KNa1.1. Its mutations are associated with many neurological disorders, such as leukodystrophy, leukoencephalopathy, West syndrome, Ohtahara syndrome, early myoclonic encephalopathy, focal epilepsy, and multifocal epilepsy. A clinical case of a typical course of KCNT1-associated epilepsy with early onset (in the first half of life), focal and asynchronous paroxysms, psychomotor retardation, and drug resistance is presented. The effectiveness of the anticonvulsants used and the nature of pharmacological resistance were analyzed. The applicability of four «Drug Resistance Hypotheses» to this case is shown: genetic, since the pathogenesis of this particular case is based on a change in the properties of potassium channels; a change in the sensitivity of the anticonvulsant targets explains the intermittent (according to Schmidt and Löscher) nature of resistance. The «Neural Networks Hypothesis» is illustrated by the change of encephalographic indicators from multifocal epileptiform activity with an intact background to pronounced dysrhythmia with periods of the «burst-suppression» pattern after several months. All these features, combined, refer to the «Intrinsic Severity» hypothesis by Rogawski and Johnson, since the child's disease was initially severe due to the intensity and frequency of epileptic seizures. As a result, a conclusion was made about the complexity of the refractoriness formation mechanisms, even in cases with a simple and understandable pathogenesis of channelopathy.

Rare variants in GRIA3, the gene encoding the GluA3 subunit of amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors (AMPARs), are associated with defects in early brain development. Disease-causing variants are generally categorised as either loss of function (LoF) or gain of function (GoF) that appear to be linked to different symptoms. Here, we reported a de novo variant (N651D) that has mixed LoF and GoF in a female patient with a devastating developmental and epileptic encephalopathy, parkinsonism and cortical malformation. N651D is located in the M3 segment, which forms the filter pore of AMPAR tetramers. Interestingly, functional assays revealed that glutamate induced no currents in GluA3_N651D homomeric receptors, likely indicating an LoF effect. However, when co-expressed with the GluA2 subunit, the GluA2/A3_N651D heteromeric receptors showed slower deactivation and desensitisation curves, along with elevated non-desensitising steady-state currents, features typically observed in GoF variants. We speculate that variants with mixed LoF and GoF effects may lead to a more devastating phenotype compared with variants with GoF effects only.