Amyloid beta precursor protein (APP) is a 100-140 kDa transmembrane glycoprotein existing as several isoforms. The amino acid sequence of APP contains the amyloid domain (A-beta), which can be released by a two-step proteolytic cleavage. It is expressed in all fetal tissues examined with highest levels in brain, kidney, heart and spleen. APP acts as a cell surface receptor and performs physiological functions on the surface of neurons relevant to neurite growth, neuronal adhesion and axonogenesis. It is also involved in cell mobility and transcription regulation through protein-protein interactions.