Bartter Syndrome: A group of disorders caused by defective salt reabsorption in the ascending LOOP OF HENLE. It is characterized by severe salt-wasting, HYPOKALEMIA; HYPERCALCIURIA; metabolic ALKALOSIS, and hyper-reninemic HYPERALDOSTERONISM without HYPERTENSION. There are several subtypes including ones due to mutations in the renal specific SODIUM-POTASSIUM-CHLORIDE SYMPORTERS.Solute Carrier Family 12, Member 1: Na-K-Cl transporter in the ASCENDING LIMB OF LOOP OF HENLE. It mediates active reabsorption of sodium chloride and is inhibited by LOOP DIURETICS such as FUROSEMIDE; and BUMETANIDE. Mutations in the gene encoding SLC12A1 are associated with a BARTTER SYNDROME.Gitelman Syndrome: An inherited renal disorder characterized by defective NaCl reabsorption in the convoluted DISTAL KIDNEY TUBULE leading to HYPOKALEMIA. In contrast with BARTTER SYNDROME, Gitelman syndrome includes hypomagnesemia and normocalcemic hypocalciuria, and is caused by mutations in the thiazide-sensitive SODIUM-POTASSIUM-CHLORIDE SYMPORTERS.Sodium-Potassium-Chloride Symporters: A subclass of symporters that specifically transport SODIUM CHLORIDE and/or POTASSIUM CHLORIDE across cellular membranes in a tightly coupled process.Failure to Thrive: A condition of substandard growth or diminished capacity to maintain normal function.Fanconi Syndrome: A hereditary or acquired form of generalized dysfunction of the PROXIMAL KIDNEY TUBULE without primary involvement of the KIDNEY GLOMERULUS. It is usually characterized by the tubular wasting of nutrients and salts (GLUCOSE; AMINO ACIDS; PHOSPHATES; and BICARBONATES) resulting in HYPOKALEMIA; ACIDOSIS; HYPERCALCIURIA; and PROTEINURIA.Chloride Channels: Cell membrane glycoproteins that form channels to selectively pass chloride ions. Nonselective blockers include FENAMATES; ETHACRYNIC ACID; and TAMOXIFEN.Potassium Channels, Inwardly Rectifying: Potassium channels where the flow of K+ ions into the cell is greater than the outward flow.Syndrome: A characteristic symptom complex.Mutation, Missense: A mutation in which a codon is mutated to one directing the incorporation of a different amino acid. This substitution may result in an inactive or unstable product. (From A Dictionary of Genetics, King & Stansfield, 5th ed)Mutation: Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.