The importance of NaPi-IIa/SLC34A1 and NaPi-IIc/SLC34A3 for phosphate homeostasis is impressively underlined by the clinical problems seen in patients with inactivating mutations in these transporters leading to hypophosphatemia, hyperphosphaturia, hypercalcemia and –calciuria with kidney stones and nephrocalcinosis and in the case of NaPi-IIc also severe bone defects1,17,18,22,27. The gene discussed is SLC34A1; the disease is hypophosphatemia.