[Tissue-nonspecific alkaline phosphatase and hypophosphatasia]

There are four isozymes for human alkaline phosphatase (ALP) : tissue-nonspecific ALP (TNSALP), intestinal ALP, placental ALP and germ cell ALP. We present a brief history of TNSALP and review progress in research on it and a rare inborn error of metabolism called hypophosphatasia (HPP), which is caused by various loss-of-function mutations in the ALPL gene encoding TNSALP. HPP is characterized by decreased levels of serum ALP activity and defect in mineralization of bone and teeth, thus establishing the direct link between TNSALP and biomineralization. In addition to its 3D structure, studies on TNSALP mutants expressed in mammalian cells have revealed how each mutation affects the structure and function of TNSALP at the molecular level, which contributes to our understanding of the molecular basis of HPP.