Involvement of mTOR pathway in neurodegeneration in NSF-related developmental and epileptic encephalopathy.

Membrane fusion is mediated by soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. During neurotransmitter exocytosis, SNARE proteins on a synaptic vesicle and the target membrane form a complex, resulting in neurotransmitter release. N-ethylmaleimide-sensitive factor (NSF), a homohexameric ATPase, disassembles the complex, allowing individual SNARE proteins to be recycled. Recently, the association between pathogenic NSF variants and developmental and epileptic encephalopathy (DEE) was reported; however, the molecular pathomechanism of NSF-related DEE remains unclear. Here, three patients with de novo heterozygous NSF variants were presented, of which two were associated with DEE and one with a very mild phenotype. One of the DEE patients also had hypocalcemia from parathyroid hormone deficiency and neuromuscular junction impairment. Using PC12 cells, a neurosecretion model, we show that NSF with DEE-associated variants impaired the recycling of vesicular membrane proteins and vesicle enlargement in response to exocytotic stimulation. In addition, DEE-associated variants caused neurodegenerative change and defective autophagy through overactivation of the mammalian/mechanistic target of rapamycin (mTOR) pathway. Treatment with rapamycin, an mTOR inhibitor or overexpression of wild-type NSF ameliorated these phenotypes. Furthermore, neurons differentiated from patient-derived induced pluripotent stem cells showed neurite degeneration, which was also alleviated by rapamycin treatment or gene correction using genome editing. Protein structure analysis of NSF revealed that DEE-associated variants might disrupt the transmission of the conformational change of NSF monomers and consequently halt the rotation of ATP hydrolysis, indicating a dominant negative mechanism. In conclusion, this study elucidates the pathomechanism underlying NSF-related DEE and identifies a potential therapeutic approach.

Long-read sequencing identifies an SVA_D retrotransposon insertion deep within the intron of ATP7A as a novel cause of occipital horn syndrome.

BACKGROUND: SINE-VNTR-Alu (SVA) retrotransposons move from one genomic location to another in a 'copy-and-paste' manner. They continue to move actively and cause monogenic diseases through various mechanisms. Currently, disease-causing SVA retrotransposons are classified into human-specific young SVA_E or SVA_F subfamilies. In this study, we identified an evolutionarily old SVA_D retrotransposon as a novel cause of occipital horn syndrome (OHS). OHS is an X-linked, copper metabolism disorder caused by dysfunction of the copper transporter, ATP7A. METHODS: We investigated a 16-year-old boy with OHS whose pathogenic variant could not be detected via routine molecular genetic analyses. RESULTS: A 2.8 kb insertion was detected deep within the intron of the patient's ATP7A gene. This insertion caused aberrant mRNA splicing activated by a new donor splice site located within it. Long-read circular consensus sequencing enabled us to accurately read the entire insertion sequence, which contained highly repetitive and GC-rich segments. Consequently, the insertion was identified as an SVA_D retrotransposon. Antisense oligonucleotides (AOs) targeting the new splice site restored the expression of normal transcripts and functional ATP7A proteins. AO treatment alleviated excessive accumulation of copper in patient fibroblasts in a dose-dependent manner. Pedigree analysis revealed that the retrotransposon had moved into the OHS-causing position two generations ago. CONCLUSION: This is the first report of a human monogenic disease caused by the SVA_D retrotransposon. The fact that the evolutionarily old SVA_D is still actively transposed, leading to increased copy numbers may make a notable impact on rare genetic disease research.

A 37-Year-Old Man With Intellectual Disability Discovered to Have Aspartylglucosaminuria: Implications for the Diagnosis of Genetic Causes.

Objectives: The causes of intellectual disability (ID) are varied, with as many as 1,400 causative genes. We attempted to identify the causative gene in a patient with long-standing undiagnosed ID. Methods: Although this was an isolated case with no family history, we searched for the causative gene using trio-based whole-exome sequencing (trio-WES), because severe ID is often caused by genetic variations, and inherited metabolic disorders (IMDs) are assumed to be the cause when regression and epilepsy occur. Results: We identified homozygous donor splice-site variants in the AGA gene (aspartylglucosaminidase; NM_000027.4) Chr4(GRCh38):g. 177436275C>A, c.698+1G>T. This gene is implicated in aspartylglucosaminuria (AGU; OMIM #208400) and originated from both of the patient's parents. We confirmed the pathogenicity of the variant by detecting the splicing defect in cDNA from the patient's blood and accumulation of aberrant metabolites in the patient's urine. Discussion: We discuss how to more readily achieve an accurate diagnosis for patients with undiagnosed intellectual disabilities. Medical practitioners' awareness of the characteristics of the disease leading to clinical suspicion in patients with matching presentations, and the performance of newborn screening when possible, is important for the diagnosis of ID. In addition, the characteristic symptoms and course of the disease give rise to suspicion of IMDs. Given our results, we consider trio-WES to be a powerful method for identifying the causative genes in cases of ID with genetic causes.

Ketogenic Diet Therapy for Intractable Epilepsy in Infantile Alexander Disease: A Small Case Series and Analyses of Astroglial Chemokines and Proinflammatory Cytokines.

In infantile Alexander disease (iAxD), one of the serious symptoms is intractable epilepsy, and some reports have suggested that neuroinflammation may be involved in the pathophysiology of the disease. Drug-resistant seizures adversely affect not only the quality of life of the caregivers and patients, but also patients' lifespan. Thus, controlling epilepsy is clinically important. For intractable childhood epilepsy, ketogenic diet therapy (KDT) is well-established, but its effects on iAxD have not been characterized. Here, we describe the use of KDT in three iAxD patients experiencing drug-resistant seizures. In all three cases, the formerly intractable epilepsies were well controlled by KDT. However, the brain magnetic resonance imaging findings deteriorated even after the epilepsy was controlled. In addition, the concentrations of monocyte chemotactic protein-1 and proinflammatory cytokines in the cerebrospinal fluid of the patients remained still high. KDT is effective in controlling epilepsy in iAxD. Our results clinically support previous reports arguing the involvement of neuroinflammation in the pathophysiology of iAxD.　Although KDT cannot prevent disease progression, earlier initiation might contribute to a better prognosis.

Isolated sixth nerve palsy as an initial presentation of primary angiitis of the central nervous system.

BACKGROUND: Primary angiitis of the central nervous system (PACNS) is a newly-emerging disease, and it is known that early diagnosis with treatment is important for the improvement of prognosis. CASE DESCRIPTION: Here, we report the case of a previously healthy 13-year-old girl who presented with right eye abduction failure, attributed to isolated right sixth nerve palsy, as the initial symptom of PACNS. Magnetic resonance angiography (MRA) showed stenosis in the distal portion of the right internal carotid artery, and delay alternating with nutation for tailored excitation (DANTE)-prepared contrast-enhanced magnetic resonance imaging confirmed vasculitis at the same site. The patient was subsequently treated with three courses of pulse corticosteroid therapy (methylprednisolone intravenously 30 mg/kg/day for three consecutive days). Diplopia completely resolved within 3 months after three course of steroid pulse therapy, and when taking 10 mg PSL daily. Follow-up MRA confirmed complete resolution of the arterial narrowing, and no relapse was observed after 2 months of steroid cessation. DISCUSSION: This case report illustrates an unusual presentation of PACNS with isolated sixth nerve palsy. PACNS was thought to cause insults on a single cranial nerve either through local spread of inflammation or hypoxic-ischemic insults on the nerve root due to involvement of feeding microvessels. The decision to perform imaging studies in cases of isolated sixth nerve palsy remains controversial because of the possibility of spontaneous recovery. Our case supports the existing literature that recommends that even an isolated symptom of unilateral abducens nerve palsy requires timely imaging studies.

Inflammatory neuropathology of infantile Alexander disease: A case report.

BACKGROUND: Alexander disease (AxD) is a rare fatal leukodystrophy caused by a dominant missense mutation in the glial fibrillary acidic protein. In a mouse model of AxD, the pathological astrocyte causes a pronounced immune response. The inflammatory environment in the brain might play an important role in the neuronal dysfunction of AxD. CASE: A 3-month-old girl diagnosed with infantile AxD presented with severe intractable seizures and a deteriorated neurological state. Steroid pulse therapy was effective at preventing the epileptic activity and progressive white matter abnormalities on magnetic resonance images, but the effect was temporary. Levels of interleukin (IL)-6, IL-8, and macrophage chemotactic protein 1 (MCP-1) in the cerebrospinal fluid were high at onset and reduced transiently after steroid pulse therapy. DISCUSSION: These results suggest that inflammatory responses of astrocyte and microglia can contribute to the neuropathology of AxD. Robust immunomodulation that targets activated astrocytes and microglia may be a novel therapeutic strategy to improve neurological prognosis in AxD.