This gene encodes a member of the nucleoside pyrophosphatase/phosphodiesterase family of enzymes that catalyzes the hydrolysis of pyrophosphate and phosphodiester bonds in nucleotide triphosphates and oligonucleotides, respectively, to generate nucleoside 5'-monophosphates. The encoded protein is a type II transmembrane glycoprotein that negatively regulates bone mineralization. Mice harboring a nonsense mutation in this gene, termed tiptoe walking (ttw), exhibit ectopic ossification of the spinal ligaments. The encoded protein binds to the insulin receptor, inhibits downstream signaling events and induces insulin resistance and glucose tolerance. This gene is located adjacent to a paralog on chromosome 10. Alternative splicing results in multiple transcript variants encoding different isoforms.