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