Congenital insensitivity to pain (biallelic LoF); erythromelalgia & PEPD (GoF)
Gene Structure & Expression
Genomic Organization & Cytogenetic Locus: 26-exon locus spanning approximately 180 kb within the chromosome 2q24.3 sodium channel gene cluster alongside SCN1A, SCN2A, SCN3A, and SCN7A, encoding four homologous six-transmembrane domains (DI–DIV) linked by intracellular loops including the IFM fast-inactivation tripeptide motif.
Cellular & Tissue Expression Profile: Selectively expressed at high density in peripheral dorsal root ganglion (DRG) and trigeminal ganglion nociceptors, sympathetic ganglion neurons, and olfactory sensory axon terminals within the olfactory bulb glomeruli.
Molecular Function & Pathways
Biochemical & Physiological Mechanism: Generates a tetrodotoxin-sensitive voltage-gated inward sodium current characterized in patch-clamp recordings by slow closed-state inactivation, enabling Nav1.7 to act as a threshold channel that amplifies subthreshold generator potentials produced by thermal, mechanical, and chemical transducers before Nav1.8 initiates the all-or-none action potential upstroke.
Clinical & Therapeutic Significance
Human Genetic Variants & Disease Phenotypes: Biallelic nonsense or frameshift loss-of-function mutations cause congenital insensitivity to pain (CIP) accompanied by anosmia without autonomic or motor neuropathy, whereas heterozygous gain-of-function missense variants hyperpolarize activation in inherited erythromelalgia (IEM) or impair fast inactivation in paroxysmal extreme pain disorder (PEPD).
Therapeutic & Clinical Pharmacology: High-priority non-opioid analgesic target pursued via state-dependent small-molecule pore and voltage-sensor blockers, dead-Cas9 epigenetic repressors (dCas9-KRAB), antisense oligonucleotides, and siRNA delivery to dorsal root ganglia.