SFTPD and pulmonary alveolar microlithiasis: Cluster 3 markers include lysosomal associated membrane protein 3 (LAMP3), multiple surfactant genes such as SFTPC, SFTPB and SFTPD, solute carrier family 34 member 2 (SLC34A2) which encodes a pH-sensitive and sodium-dependent phosphate transporter, which is mutated in pulmonary alveolar microlithiasis, a disease characterized by calcium phosphate deposits in the lung.