KCNK9 (Potassium Two Pore Domain Channel Subfamily K Member 9): KCNK9 encodes a two-pore-domain potassium channel, which belongs to the potassium channel family. These channels assist in regulating the resting membrane potential and controlling neuronal excitability. Mutations in KCNK9 are associated with Birk-Barel mental retardation dysmorphism syndrome, highlighting its crucial role in neural development and function.