KCNJ3 and Down syndrome: GIRK2 subunit is widely expressed in the brain, forms functional heterotetramers (GIRK1–GIRK2, GIRK2–GIRK3) and homotetramers (GIRK2–GIRK2) and has been implicated in various functions and pathologies [66,67], such as learning and memory, reward, motor coordination, and Down syndrome.