SCN9A (Sodium Voltage-Gated Channel Alpha Subunit 9): SCN9A encodes a voltage-gated sodium channel (NaV1.7) that is highly expressed in the peripheral nervous system, especially in pain-sensing neurons (nociceptors). Mutations in SCN9A can cause gain- or loss-of-function effects, leading to conditions such as erythromelalgia or congenital insensitivity to pain. As a key modulator of pain sensation, NaV1.7 is an important target for developing new analgesics.