Aberrant production, clearance and deposition of amyloid-beta protein (A beta) in the human brain have been implicated in the aetiology of Alzheimer disease (AD). gamma-Secretase is the enzyme responsible for generating various Ab species, such as A beta 40 and toxic A beta 42. Recently, genome-wide association studies in late-onset AD patients have identified the endocytosis-related phosphatidylinositol-binding clathrin assembly protein (PICALM) gene as a genetic risk factor for AD. We previously found that the loss of expression of CALM protein encoded by PICALM affects the ratio of production of A beta 42, through the regulation of the clathrin-mediated endocytosis of c-secretase. Here, we show that the binding capacity of the assembly protein 180 N-terminal homology (ANTH) domain of CALM to phosphatidylinositol-4,5-biphosphate, as well as to nicastrin, is critical to the modulation of the internalization of gamma-secretase and to the A beta 42 production ratio. Moreover, reduction of CALM decreases Ab deposition as well as brain levels of insoluble A beta 42 in vivo. These results suggest that CALM expression modifies AD risk by regulating Ab pathology.