There are at least four distinct but related alkaline phosphatases: intestinal, placental, placental-like, and liver/bone/kidney (tissue non-specific). The first three are located together on chromosome 2 while the tissue non-specific form is located on chromosome 1. The product of this gene is a membrane bound glycosylated enzyme, also referred to as the heat stable form, that is expressed primarily in the placenta although it is closely related to the intestinal form of the enzyme as well as