A form of hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is known to occur due to mutations in the proximal tubule type 2c sodium-phosphate cotransporter (NaPi2c). Defective phosphate transport and hypophosphatemia in this case result in appropriately increased 1, 25-dihydroxyvitamin D3 levels, thus leading to hypercalciuria.