ADH1A and Hypercalciuria: In patients with ADH1, two mechanisms contribute to hypercalciuria: first, low concentrations of PTH, which normally induces renal reabsorption of calcium from the primary filtrate; second, increased activation of the mutated CASR through extracellular calcium in the thick ascending limb of the Loop of Henle, which leads to even more profound hypercalciuria for any given blood calcium level [5].