Thus, dysfunctions of principal cell–specific transporters such as ENaC or AQP2 or its receptors (mineralocorticoid or vasopressin receptors) caused by mutations or by compounds present in the environment (lithium, antibiotics, etc.)have been demonstrated in a variety of syndromes (Liddle, pseudohypoaldosteronism type‐1, diabetes insipidus, etc.)affecting salt, potassium, and water balance. The gene discussed is AQP2; the disease is diabetes insipidus.