ANKH (progressive ankylosis protein homolog) is a multi-pass transmembrane protein involved in bone mineralization and joint maintenance. ANKH is a ubiquitously expressed protein with high expression levels in the embryonic developing articular cartilage of joints in the elbow, wrist, shoulders and digits. Expression of ANKH is regulated by cytokines and various growth factors. ANKH functions as a transporter, regulating the extracellular transport of inorganic pyrophosphates (PPi). The extracellular level of inorganic pyrophosphates can both inhibit and promote different types of pathologic mineralization. Mutations in ANKH are associated with various human skeletal defects including calcium pyrophosphate deposition disease (CPPD) and craniometaphyseal dysplasia Jackson type (CMDJ).