JPND BRain Imaging, cognition, Dementia and next generation GEnomics

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Establishing efficient prevention strategies for dementia and Alzheimer disease (AD) is a major health priority for the coming years. An important hurdle is that pathological processes leading to AD begin many years before clinical diagnosis, hence efficient prevention should be initiated very early. This requires identifying individuals in the general population who are at high risk of developing dementia and exploring the molecular pathways underlying the structural brain alterations that precede the occurrence of dementia, an essential step for identifying novel relevant drug targets. To tackle these important questions we propose to explore the genetic and epigenetic determinants of quantitative MRI-markers of brain aging that are powerful predictors of dementia/AD risk, and to examine the clinical significance of the markers in a population-based setting. Leveraging the extensive information collected within the largest European population-based cohort studies with neuroimaging data, we will first search for genetic variants associated with established and novel MRI-markers of brain aging, focusing particularly on rare variants, using both an agnostic and candidate locus approach (loci identified through genome-wide association studies [GWAS] as associated AD or with MRI-markers of brain aging). In contrast with GWAS signals, rare variants may lead to the discovery of causal variants, and have hardly been explored in association with structural MRI-markers. Second, we will take an original lifetime perspective, through examination of samples in various age categories spanning from young adulthood to older age, many of which with repeated MRI and blood sampling. Indeed, there is increasing evidence that early-life factors play an important role in the occurrence of late-onset neurodegenerative diseases. We propose an innovative exploration of lifetime changes in methylation associated with structural brain alterations using a novel bisulfite sequencing technology, to help identify functional and disease relevant variants. We will also study the modifying effect of vascular risk factors and socio-economic status on genetic/epigenetic determinants of brain aging. Third, we will explore the clinical significance of genetic and epigenetic markers we identify by examining their association with cognitive performance, cognitive decline and risk of dementia/AD, capitalizing on the elaborate cognitive testing and prospective dementia surveillance available in all studies.