Sodium channel protein type 2 subunit alpha, also known as Nav1.2, is an ion channel protein encoded by the SCN2A gene in humans. It represents one member of the sodium channel alpha subunit gene family. The SCN2A gene is located on chromosome 2 (2q24.3) in proximity to two other voltage-gated sodium channel genes, namely SCN1A and SCN9A. Nav1.2 is distributed throughout the human central nervous system where it plays a major role in the initiation and propagation of action potentials. It is absent from peripheral tissues, with the exception of enteric neurons. Pathologic mutations in the SCN2A gene cause a broad spectrum of neurological conditions, such as epilepsy, autism spectrum disorder (ASD), intellectual disability (ID) and/or developmental delay, called SCN2A-related disorders.
Structure The SCN2A gene is composed of 27 exons and comprises more than 150 kilobases. There are two major splice variants known, a neonatal isoform and an adult isoform, which differ in one amino acid at position 209 (Asn versus Asp). The neonatal isoform might limit neuronal excitability during development. The voltage-gated sodium channel Nav1.2 encoded by the SCN2A gene consists of 2005 amino acids. This single polypeptide forms a pseudotetrameric channel of four similar domains (I - IV) where each domain contains 6 transmembrane segments, including a voltage sensing region, a pore forming region and an ion-selectivity filter. In the living organism, Nav1.2 is a transmembrane glycoprotein complex composed of a large alpha subunit (encoded by the SCN2A gene) and one or more regulatory beta subunits (encoded by SCNxB genes).
Function The principal function of Nav1.2, similar to other members of the voltage-gated sodium channel family, is to mediate sodium influx into neurons upon membrane depolarization, thereby generating and propagating action potentials across distinct neuronal subtypes. Nav1.2 functions mainly in excitatory neurons in cortical structures similar to Nav1.6, whereas expression of Nav1.1 (encoded by the SCN1A gene) is found in mutual distinct, inhibitory neuronal classes. However, the distribution of Nav1.2 changes during development. Nav1.2 channels are initially expressed at the axon initial segments (the site of action potential initiation) of excitatory pyramidal cells in both hippocampal and cortical excitatory cells. While these levels remain constant in the hippocampus, in cortical excitatory cells, Nav1.2 becomes restricted to the portion of the axon initial segment closest to the cell body and in dendrites at the age of 1–2 years in humans. Nav1.6 gradually becomes the predominant channel type at the distal axon initial segment and axonal nodes of Ranvier. In mature neurons, Nav1.2 is distributed only throughout unmyelinated axons. In contrast, its expression pattern in the cerebellum seems to persist throughout development, suggesting distinct roles for Nav1.2 in mature neurons of the neocortex and cerebellum. When Nav1.6 takes over the initiation of action potentials, Nav1.2 might play a crucial role in driving their backpropagation into dendrites. This backpropagation could impact activity-dependent processes such as synaptic maturation, plasticity, and gene transcription. The activity of Nav1.2 is influenced by several factors, such as protein-protein interactions, posttranslational modifications (e.g. phosphorylation, pamitoylation), and changes in intracellular Ca2+ concentration.
Clinical significance Mutations in the SCN2A gene can cause a broad spectrum of disorders collectively referred to as SCN2A-related disorders. These include cases of ASD, self-limited epilepsy, early infantile developmental and epileptic encephalopathy, later onset developmental and epileptic encephalopathy, infantile spasms, SCN2A-related disorders without epilepsy, episodic ataxia, and further movement disorders. Two major groups of SCN2A mutations can be distinguished based on their functional consequences and response to seizure medication: gain of function mutations, typically associated with seizure onset within the first three months of life, and loss of function mutations, in which seizures begin after the first three months or may never occur. The former group tends to benefit from treatment with sodium channel blockers, whereas in the latter, such treatment is often ineffective or may even exacerbate seizures. Notably, SCN2A is known to be the most prominent genetic risk factor for autism-spectrum-disorders. SCN2A gene mutations have also been identified in bitemporal glucose hypometabolism, and bipolar disorder. Furthermore, mutations in SCN2A have been demonstrated to impair enteric neuron migration during development, which may result in gastrointestinal dysmotility, consistent with gastric motility symptoms reported in ASD patients with underlying SCN2A mutations.
See also paralytic - SCN2A ortholog in Drosophila
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External links
Patient advocacy organizations (PAO / PAG) Cure SCN2A (Australia) FamiliesSCN2A Foundation SCN2A Australia SCN2A Brasil SCN2A Georgia SCN2A Europe SCN2A Foundation SCN2A Germany e. V. SCN2A Italia SCN2A UK SCN2A Ukraine
Other links ICD-10-CM Code (QA0.0101) effective October 1, 2025 - SCN2A-related neurodevelopmental disorder[1] International SCN2A Awareness Day - February 24th SCN2A+protein,+human at the U.S. National Library of Medicine Medical Subject Headings (MeSH) Overview of all the structural information available in the PDB for UniProt: Q99250 (Sodium channel protein type 2 subunit alpha) at the PDBe-KB.
This article incorporates text from the United States National Library of Medicine, which is in the public domain.
