SLC34A1 and 2 encode Na+/Pi cotransporters, which cotransport divalent phosphate (PO4(2-), Pi) with 3 Na+ ions. SLC34A1 is an important Pi transporter mainly expressed in renal proximal tubules where it plays a major role in Pi homeostasis. Defects in SLC34A1 are the cause of hypophosphatemic nephrolithiasis/osteoporosis type 1 (NPHLOP1; MIM:612286), disease characterised by decreased renal phosphate absorption, hypophosphatemia, hyperphosphaturia, hypercalciuria, nephrolithiasis and implicated in the formation of renal calcium stones and/or bone demineralisation (Prie et al. 2002, Prie et al. 2004, Choi 2008, Boskey et al. 2013, Forster et al. 2013).