SCN9A

SCN9A Full Name

sodium channel, voltage gated, type IX alpha subunit

SCN9A Introduction

Introduction
The SCN9A (sodium voltage-gated channel alpha subunit 9) gene encodes the Nav1.7 voltage-gated sodium channel, a protein that has emerged as one of the most clinically significant ion channels in human medicine. This channel serves as the master regulator of pain perception, acting as the gatekeeper for pain signal transmission from peripheral nociceptors to the central nervous system. The extraordinary clinical importance of SCN9A stems from a striking genetic paradox: gain-of-function mutations cause debilitating pain syndromes characterized by spontaneous burning pain, while loss-of-function mutations result in a complete inability to perceive pain, with affected individuals experiencing fractures, burns, and injuries without any discomfort. This gene has consequently become the focus of intensive drug development efforts aimed at creating novel non-addictive analgesics that target Nav1.7 selectively.

Figure 1. Strcuture of SCN9A.

Genomic Characteristics
The human SCN9A gene is located on chromosome 2 at position 2q24.3, spanning an exceptionally large genomic interval of approximately 180.8 kilobases. The gene contains 27 exons, with 26 coding exons that produce a protein-coding transcript of 113,085 base pairs. The genomic organization includes a non-coding exon 1 located approximately 64,000 nucleotides upstream of the translation start site, a feature characteristic of voltage-gated sodium channel genes. Multiple transcript variants generated through alternative splicing have been identified, with isoform 1 expressed preferentially in the central and peripheral nervous system, while isoform 2 shows preferential expression in the dorsal root ganglion. The gene exhibits extreme intolerance to loss-of-function variation in population databases, reflecting its critical physiological role, and its complex genomic structure with large introns creates susceptibility to deep-intronic splicing mutations that can disrupt channel function.

Gene Regulation and Transcriptional Control
The SCN9A promoter is located approximately 64 kilobases upstream of the translation start site and exhibits features characteristic of a TATA-less promoter within a well-defined CpG island. Multiple transcription initiation sites have been identified within a short genomic region, adding regulatory flexibility. The promoter responds to numerous factors that modulate Nav1.7 expression in physiological and pathophysiological contexts. Nerve growth factor (NGF) upregulates SCN9A transcription through signaling pathways that activate transcription factors including Brn-3a, a POU domain transcription factor that binds the SCN9A promoter and enhances channel expression. Phorbol esters, which activate protein kinase C, and retinoic acid also increase SCN9A promoter activity and mRNA levels. This regulation explains the upregulation of Nav1.7 observed in inflammatory pain models, where NGF released from inflamed tissues drives increased channel expression in DRG neurons, contributing to peripheral sensitization and hyperalgesia. Conversely, the repressor element REST (RE1-silencing transcription factor) can silence sodium channel gene expression in non-neuronal cells, contributing to the neuron-specific expression pattern.

Alternate Names for SCN9A

SCN9A; sodium channel; voltage gated; type IX alpha subunit; PN1; ETHA; NENA; SFNP; FEB3B; NE-NA; GEFSP7; HSAN2D; Nav1.7; sodium channel protein type 9 subunit alpha; hNE-Na; peripheral sodium channel 1; neuroendocrine sodium channel; sodium channel protein type IX subunit alpha; voltage-gated sodium channel alpha subunit Nav1.7; voltage-gated sodium channel subunit alpha Nav1.7; sodium channel; voltage-gated; type IX; alpha subunit; sodium channel; voltage-gated; type IX; alpha polypeptide; anti-NAv1.7