B6-hSCN2A Mice

Figure 1. Gene editing strategy of B6-hSCN2A mice. The sequence from the ATG start codon to the TAA stop codon of mouse Scn2a was replaced with the sequence from the ATG start codon to the TAA stop codon of human SCN2A.

1. Detection of human SCN2A gene expression

Figure 2. Human SCN2A gene expression in the brain and lungs of wild-type mice (B6N) and B6-hSCN2A mice (hSCN2A). RT-qPCR results show that there was the expression of human SCN2A gene in the brain and lungs of B6-hSCN2A mice, while there was no expression in B6N mice. (ND: Not detected)

2. Detection of mouse Scn2a gene expression

Figure 3. Mouse Scn2a gene expression in the brain and lungs of wild-type mice (B6N) and B6-hSCN2A mice (hSCN2A). RT-qPCR results show that there was expression of mouse Scn2a gene in the brain and lungs of B6N mice, while there was no expression in B6-hSCN2A mice.

1. Basic information about the SCN2A gene

https://rddc.tsinghua-gd.org/gene/6326

2. SCN2A clinical variants

https://rddc.tsinghua-gd.org/ai/pathogenicity/e2ae5fe8754742899d013c022f53f537

3. Disease introduction

Epilepsy is a chronic non-infectious disease of the brain characterized by recurrent seizures. According to the World Health Organization, an estimated 5 million people worldwide are diagnosed with epilepsy each year, making it one of the most common neurological disorders globally. During an epileptic seizure, a part of the body or the entire body may experience brief involuntary convulsions, sometimes accompanied by loss of consciousness and urinary incontinence. Patients often have more physical problems (such as fractures and abrasions related to seizures) and a higher proportion of psychological disorders, including anxiety and depression. Compared to the general population, epilepsy can triple the risk of premature death for patients, with the highest premature mortality rates in low- and middle-income countries and rural areas [1]. The causes of epilepsy include structural, genetic, infectious, metabolic, and immune factors. Currently, the pathogenesis of approximately 50% of patients worldwide remains unknown. With the widespread use of genetic testing in pediatric neurology, more than half of epileptic children are believed to have a genetic cause. Voltage-gated sodium ion channel genes such as SCN1A, SCN2A, SCN3A, and SCN8A are the main pathogenic genes. Single nucleotide variations (SNVs) are the most common pathogenic variations in genetic epilepsy. SNVs can lead to loss or gain of function of affected ion channels, such as epileptic encephalopathies (DEEs) associated with SCN2A ^[2-4].

4. SCN2A gene and mutations

SCN2A (sodium voltage-gated channel alpha subunit 2) gene is the second most common epilepsy-causing gene after SCN1A. This gene encodes the α2 subunit of the voltage-gated sodium channel (Nav1.2). The voltage-gated sodium channel is a transmembrane glycoprotein complex composed of a large α subunit with four repeated structural domains and one or more regulatory β subunits. It plays a role in the generation and propagation of neuronal and muscle action potentials, mainly expressed in the initial segment of the axon of excitatory neurons and unmyelinated axons. This protein is widely distributed in the cerebral cortex, hippocampus, striatum, and midbrain. Mutations in the SCN2A gene are associated with a range of neurological and epileptic disorders, such as epilepsy, intellectual disability, ASD, schizophrenia, and periodic ataxia, and are inherited in an autosomal dominant manner. Most epilepsies caused by SCN2A variants occur in early childhood, with a wide range of phenotypes, from benign self-limiting epilepsy to developmental epilepsy and epileptic encephalopathy. SCN2A gene mutations are distributed in different regions without obvious hotspots, and missense mutations are the most common type. V261M, R853Q, H1853R, E999K, E1211K, R1319Q, A1500T, R1629H, and P1658S are recurrent mutations ^[4].

5. Function of non-coding DNA sequences

Both the splicing isoforms of the SCN2A gene and the developmental stage of neurons affect the impact of NaV1.2 variants associated with early-onset epileptic encephalopathy (EOEE) on neuronal excitability ^[6]. Research shows that the c.1035-7A>G mutation activates a cryptic intron acceptor site, leading to a 6-nucleotide extension of exon 9 (NP_066287.2:p. (Gly345_Gln346insTyrSer)) ^[7].

6. SCN2A-targeted gene therapy

Currently, most drug treatments for epilepsy are relatively imprecise methods, whose main purpose is to reduce the likelihood of epileptic seizures rather than affect the underlying disease process. Most approved antiepileptic drugs are anticonvulsant drugs rather than antiepileptic drugs. Sodium channel blockers (SCBs) may be an effective and precise drug for treating epilepsy caused by SCN2A mutations (such as phenytoin) ^[5]. As more and more epilepsy gene causes are discovered this not only enhances the understanding of the potential epileptic process but also makes targeted gene therapy possible. The ideal anti-epileptic therapy can affect functional changes caused by specific pathogenic gene mutations. Praxis Precision Medicines is developing a small molecule drug (PRAX-562) that selectively inhibits persistent sodium currents as a sodium channel blocker, for the treatment of epileptic encephalopathy (DEE) associated with SCN2A and SCN8A [8]. In addition, another ASO drug developed by the company, elsunersen (PRAX-222), has obtained the Priority Medicines (PRIME) certification from the European Medicines Agency (EMA) for the treatment of SCN2A gain-of-function (GoF) developmental epileptic encephalopathy (DEE) ^[9].

In summary, the SCN2A gene is a significant pathogenic gene for epilepsy. Constructing a humanized mouse model helps develop effective and precise drugs for the treatment of epilepsy caused by SCN2A mutations. SCN2A gene humanized mice from Cyagen can be used for preclinical research on epilepsy and customized services can also be provided for different point mutations.