The etiology of hypercalciuria is complex given that urinary excretion of calcium is the end result of an interplay between three organs—namely, the gastrointestinal tract, bone, and kidney—which is further orchestrated by hormones, such as 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3), parathyroid hormone (PTH), calcitonin, fibroblast growth factor (FGF-23), etc. Often, a primary defect in one organ induces compensatory mechanisms in the remaining two organs, such as increased absorption of calcium in the gut secondary to a primary renal loss. The gene discussed is FGF23; the disease is Hypercalciuria.