SLC34A1 and 2 encode Na+/Pi cotransporters, which cotransport divalent phosphate (PO4(2-), Pi) with 3 Na+ ions. SLC34A2 is abundantly expressed in lung and to a lesser extent in tissues of epithelial origin including small intestine, pancreas, prostate, and kidney. Defects in SLC34A2 are a cause of pulmonary alveolar microlithiasis (PALM; MIM:265100), a rare disease characterised by the deposition of calcium phosphate microliths throughout the lungs. The disease follows a long-term progressive course, resulting in a slow deterioration of lung function. Mutations causing PALM include Q76*, G106R, K304* and N38Tfs*8 (Corut et al. 2006, Zhonghua et al. 2009).