Background：Ab derives from APP via proteolytic cleavage by proteases called a-,b- and gamma-secretase. The a-secretase cleavage precludes the formation of Ab,while the b- and gamma-cleavages generate APP components with amyloidogenic features. Amyloid beta A4 precursor protein（APP）,encoded by APP gene which locate on human chromosome 21q,is a cell surface receptor and performs physiological functions on the surface of neurons relevant to neurite growth,neuronal adhesion and axonogenesis. APP expressed in all fetal tissues and is pronounced in brain,kidney,heart and spleen,but weak in liver. Defects in APP are the cause of Alzheimer disease type 1 （AD1）.
