KCNK9 (Potassium Two Pore Domain Channel Subfamily K Member 9): KCNK9 encodes a two-pore-domain potassium channel, which is part of the potassium channel family. These channels help regulate the resting membrane potential and control neuronal excitability. Mutations in KCNK9 are linked to Birk-Barel mental retardation dysmorphism syndrome, underscoring its important role in neural development and function.