Pulmonary alveolar microlithiasis is a rare idiopathic pneumopathy characterized by diffuse intra-alveolar deposits of calcium, in the form of tiny, roundish corpuscles called 'microliths'. The consition may progress over time, leading to pulmonary fibrosis, respiratory failure, and chronic pulmonary heart disease. 

Up to 50% of all reported cases have been familial. In affected families, PAM seems to follow an autosomal recessive mode of transmission. Recently, mutations in the gene Solute Carrier Family 34, Member 2 (SLC34A2), have been found to be causal of PAM.