Alzheimer's risk variants in the clusterin gene are associated with alternative splicing

Genetic variation in CLU encoding clusterin has been associated with Alzheimer's disease (AD) through replicated genome-wide studies, but the underlying mechanisms remain unknown. Following earlier reports that tightly regulated CLU alternative transcripts have different functions, we tested CLU single nucleotide polymorphisms (SNPs) including those associated with AD for quantitative effects on individual alternative transcripts. In 190 temporal lobe samples without pathology we found that the risk allele of the AD associated SNP rs9331888 increases the relative abundance of transcript NM_203339 (P=4.3×10(-12)). Using an independent set of 115 AD and control samples, we replicated this result (p=0.0014) and further observed that multiple CLU transcripts are at higher levels in AD compared to controls. The AD SNP rs9331888 is located in the first exon of NM_203339 and therefore, it is a functional candidate for the observed effects. We tested this hypothesis by in vitro dual luciferase assays using SK-N-SH cells and mouse primary cortical neurons and found allelic effects on enhancer function, consistent with our results on post-mortem human brain. These results suggest a biological mechanism for the genetic association of CLU with AD risk and indicate that rs9331888 is one of the functional DNA variants underlying this association.