A polymorphism in CALHM1 influences Ca2+ homeostasis, Aβ levels, and Alzheimer's disease risk

Alzheimer's disease (AD) is a genetically heterogeneous disorder characterized by early hippocampal atrophy and cerebral amyloid-beta (A beta) peptide deposition. Using TissueInfo to screen for genes preferentially expressed in the hippocampus and located in AD linkage regions, we identified a gene on 10q24.33 that we call CALHM1. We show that CALHM1 encodes a multipass transmembrane glycoprotein that controls cytosolic Ca2+ concentrations and Ab levels. CALHM1 homomultimerizes, shares strong sequence similarities with the selectivity filter of the NMDA receptor, and generates a large Ca2+ conductance across the plasma membrane. Importantly, we determined that the CALHM1 P86L polymorphism (rs2986017) is significantly associated with AD in independent case-control studies of 3404 participants (allele-specific OR = 1.44, p = 2 x 10(-10)). We further found that the P86L polymorphism increases A beta levels by interfering with CALHM1-mediated Ca2+ permeability. We propose that CALHM1 encodes an essential component of a previously uncharacterized cerebral Ca2+ channel that controls Ab levels and susceptibility to late-onset AD.