SCN9A (Sodium Voltage-Gated Channel Alpha Subunit 9): SCN9A encodes a voltage-gated sodium channel (NaV1.7) that is predominantly expressed in the peripheral nervous system, particularly in pain-sensing neurons (nociceptors). Mutations in SCN9A can result in either gain- or loss-of-function effects, leading to disorders such as erythromelalgia or congenital insensitivity to pain. As a crucial regulator of pain perception, NaV1.7 is a significant target for the development of new pain-relief medications.