SLC34A2 and pulmonary alveolar microlithiasis: The changes observed in renal phosphate transporter expression in mice with NaPi-IIb deletion might explain the finding that in human pulmonary alveolar microlithiasis, a disorder caused by inactivating mutations in NaPi-IIb, patients do not exhibit significant changes in serum phosphate concentrations [47], but do have decreased FGF-23 levels and urinary phosphate excretion [48].