Protein family FAM241 in human and mouse.

FAM241B was isolated in a genome-wide inactivation screen for generation of enlarged lysosomes. FAM241B and FAM241A comprise protein family FAM241 encoding proteins of 121 and 132 amino acid residues, respectively. The proteins exhibit 25% amino acid sequence identity and contain a domain of unknown function (DUF4605; pfam15378) that is conserved from primitive multicellular eukaryotes through vertebrates.

Allele-Specific Editing of a Dominant SCN8A Epilepsy Variant Protects against Seizures and Lethality in a Murine Model.

Objective: Developmental and epileptic encephalopathies (DEEs) can result from dominant, gain of function variants of neuronal ion channels. More than 450 de novo missense variants of the sodium channel gene SCN8A have been identified in individuals with DEE.

Methods: We studied a mouse model carrying the patient Scn8a variant p.

Dentate gyrus granule cells are a locus of pathology in Scn8a developmental encephalopathy.

Gain-of-function mutations in SCN8A cause developmental and epileptic encephalopathy (DEE), a disorder characterized by early-onset refractory seizures, deficits in motor and intellectual functions, and increased risk of sudden unexpected death in epilepsy. Altered activity of neurons in the corticohippocampal circuit has been reported in mouse models of DEE. We examined the effect of chronic seizures on gene expression in the hippocampus by single-nucleus RNA sequencing in mice expressing the patient mutation SCN8A-p.

A model organism pipeline provides insight into the clinical heterogeneity of TARS1 loss-of-function variants.

Aminoacyl-tRNA synthetases (ARSs) are ubiquitously expressed, essential enzymes that complete the first step of protein translation: ligation of amino acids to cognate tRNAs. Genes encoding ARSs have been implicated in myriad dominant and recessive phenotypes, the latter often affecting multiple tissues but with frequent involvement of the central and peripheral nervous systems, liver, and lungs. Threonyl-tRNA synthetase (TARS1) encodes the enzyme that ligates threonine to tRNA in the cytoplasm.

Biallelic loss-of-function variants of SLC12A9 cause lysosome dysfunction and a syndromic neurodevelopmental disorder.

Purpose: Pathogenic variants of FIG4 generate enlarged lysosomes and neurological and developmental disorders. To identify additional genes regulating lysosomal volume, we carried out a genome-wide activation screen to detect suppression of enlarged lysosomes in FIG4 cells.

Methods: The CRISPR-a gene activation screen utilized sgRNAs from the promoters of protein-coding genes.

Long-Term Downregulation of the Sodium Channel Gene Scn8a Is Therapeutic in Mouse Models of SCN8A Epilepsy.

Objective: De novo mutations of the voltage-gated sodium channel gene SCN8A cause developmental and epileptic encephalopathy (DEE). Most pathogenic variants result in gain-of-function changes in activity of the sodium channel Na1.6, poorly controlled seizures, and significant comorbidities.

Reduction of is therapeutic in mouse models of and epilepsy.

Developmental and epileptic encephalopathies (DEEs) are severe seizure disorders with inadequate treatment options. Gain- or loss-of-function mutations of neuronal ion channel genes, including potassium channels and voltage-gated sodium channels, are common causes of DEE. We previously demonstrated that reduced expression of the sodium channel gene is therapeutic in mouse models of sodium and potassium channel mutations.

The chloride antiporter CLCN7 is a modifier of lysosome dysfunction in FIG4 and VAC14 mutants.

The phosphatase FIG4 and the scaffold protein VAC14 function in the biosynthesis of PI(3,5)P2, a signaling lipid that inhibits the lysosomal chloride transporter ClC-7. Loss-of-function mutations of FIG4 and VAC14 reduce PI(3,5)P2 and result in lysosomal disorders characterized by accumulation of enlarged lysosomes and neurodegeneration. Similarly, a gain of function mutation of CLCN7 encoding ClC-7 also results in enlarged lysosomes.

Altered phenotypes due to genetic interaction between the mouse phosphoinositide biosynthesis genes Fig4 and Pip4k2c.

Loss-of-function mutations of FIG4 are responsible for neurological disorders in human and mouse that result from reduced abundance of the signaling lipid PI(3,5)P2. In contrast, loss-of-function mutations of the phosphoinositide kinase PIP4K2C result in elevated abundance of PI(3,5)P2. These opposing effects on PI(3,5)P2 suggested that we might be able to compensate for deficiency of FIG4 by reducing expression of PIP4K2C.

Chloroquine corrects enlarged lysosomes in FIG4 null cells and reduces neurodegeneration in Fig4 null mice.

Loss-of-function mutations of FIG4 impair the biosynthesis of PI(3,5)P and are responsible for rare genetic disorders including Yunis-Varón Syndrome and Charcot-Marie-Tooth Disease Type 4 J. Cultured cells deficient in FIG4 accumulate enlarged lysosomes with hyperacidic pH, due in part to impaired regulation of lysosomal ion channels and elevated intra-lysosomal osmotic pressure. We evaluated the effects of the FDA approved drug chloroquine, which is known to reduce lysosome acidity, on FIG4 deficient cell culture and on a mouse model.

Genetic interaction between Scn8a and potassium channel genes Kcna1 and Kcnq2.

Voltage-gated sodium and potassium channels regulate the initiation and termination of neuronal action potentials. Gain-of-function mutations of sodium channel Scn8a and loss-of-function mutations of potassium channels Kcna1 and Kcnq2 increase neuronal activity and lead to seizure disorders. We tested the hypothesis that reducing the expression of Scn8a would compensate for loss-of-function mutations of Kcna1 or Kcnq2.

Social Deficits and Cerebellar Degeneration in Purkinje Cell Knockout Mice.

Mutations in the gene encoding the voltage-gated sodium channel α-subunit Nav1. 6 have been reported in individuals with epilepsy, intellectual disability and features of autism spectrum disorder. is widely expressed in the central nervous system, including the cerebellum.

Correction of the hypomorphic splice site variant in mouse strain C57BL/6J modifies the severity of encephalopathy.

gain-of-function mutations of are a significant cause of developmental and epileptic encephalopathy (DEE) (MIM: 614558). The severely affected individuals exhibit refractory seizures, developmental delay, and cognitive disabilities, often accompanied by impaired movement. Individuals with the identical variant often differ in clinical course, suggesting a role for modifier genes in disease severity.

Antisense Oligonucleotide Therapy for Neurodevelopmental Disorders.

Antisense oligonucleotides (ASOs) are short oligonucleotides that can modify gene expression and mRNA splicing in the nervous system. The FDA has approved ASOs for treatment of ten genetic disorders, with many applications currently in the pipeline. We describe the molecular mechanisms of ASO treatment for four neurodevelopmental and neuromuscular disorders.

Spontaneous seizures and elevated seizure susceptibility in response to somatic mutation of sodium channel Scn8a in the mouse.

De novo mutations of neuronal sodium channels are responsible for ~5% of developmental and epileptic encephalopathies, but the role of somatic mutation of these genes in adult-onset epilepsy is not known. We evaluated the role of post-zygotic somatic mutation by adult activation of a conditional allele of the pathogenic variant Scn8aR1872W in the mouse. After activation of CAG-Cre-ER by tamoxifen, the mutant transcript was expressed throughout the brain at a level proportional to tamoxifen dose.

Postictal Death Is Associated with Tonic Phase Apnea in a Mouse Model of Sudden Unexpected Death in Epilepsy.

Objective: Sudden unexpected death in epilepsy (SUDEP) is an unpredictable and devastating comorbidity of epilepsy that is believed to be due to cardiorespiratory failure immediately after generalized convulsive seizures.

Methods: We performed cardiorespiratory monitoring of seizure-induced death in mice carrying either a p.Arg1872Trp or p.

Sodium channelopathies in neurodevelopmental disorders.

The voltage-gated sodium channel α-subunit genes comprise a highly conserved gene family. Mutations of three of these genes, SCN1A, SCN2A and SCN8A, are responsible for a significant burden of neurological disease. Recent progress in identification and functional characterization of patient variants is generating new insights and novel approaches to therapy for these devastating disorders.

Gabra2 is a genetic modifier of Scn8a encephalopathy in the mouse.

Objective: SCN8A encephalopathy is a developmental epileptic encephalopathy typically caused by de novo gain-of-function mutations in Na 1.6. Severely affected individuals exhibit refractory seizures, developmental delay, cognitive disabilities, movement disorders, and elevated risk of sudden death.

Scn8a Antisense Oligonucleotide Is Protective in Mouse Models of SCN8A Encephalopathy and Dravet Syndrome.

Objective: SCN8A encephalopathy is a developmental and epileptic encephalopathy (DEE) caused by de novo gain-of-function mutations of sodium channel Na 1.6 that result in neuronal hyperactivity. Affected individuals exhibit early onset drug-resistant seizures, developmental delay, and cognitive impairment.

SCN8A encephalopathy: Mechanisms and models.

De novo mutations of the neuronal sodium channel SCN8A have been identified in approximately 2% of individuals with epileptic encephalopathy. These missense mutations alter the biophysical properties of sodium channel Nav1.6 in ways that lead to neuronal hyperexcitability.

Biallelic inherited SCN8A variants, a rare cause of SCN8A-related developmental and epileptic encephalopathy.

Objective: Monoallelic de novo gain-of-function variants in the voltage-gated sodium channel SCN8A are one of the recurrent causes of severe developmental and epileptic encephalopathy (DEE). In addition, a small number of de novo or inherited monoallelic loss-of-function variants have been found in patients with intellectual disability, autism spectrum disorder, or movement disorders. Inherited monoallelic variants causing either gain or loss-of-function are also associated with less severe conditions such as benign familial infantile seizures and isolated movement disorders.

CRISPR knockout screen implicates three genes in lysosome function.

Defective biosynthesis of the phospholipid PI(3,5)P underlies neurological disorders characterized by cytoplasmic accumulation of large lysosome-derived vacuoles. To identify novel genetic causes of lysosomal vacuolization, we developed an assay for enlargement of the lysosome compartment that is amenable to cell sorting and pooled screens. We first demonstrated that the enlarged vacuoles that accumulate in fibroblasts lacking FIG4, a PI(3,5)P biosynthetic factor, have a hyperacidic pH compared to normal cells'.