Association of short tandem repeats with neuropathological features in late‐onset of Alzheimer’s disease brains

Abstract

AbstractBackgroundLate‐Onset Alzheimer’s Disease (LOAD) is characterized by genetic heterogeneity and there is no single model explaining the genetic mode of inheritance. Short tandem repeats (STRs), which are hyper‐mutable sequences in the human genome could explain some of the missing heritability in LOAD. STRs are involved in several neuro‐degenerative disorders. We systematically evaluated the impact of 31 disease‐associated STRs on neuropathological LOAD features.MethodFrom whole‐genome sequencing (WGS) data in for 1,134 unrelated individuals of European ancestry from Religious Orders Study (ROS) and Rush Memory and Aging project (MAP) cohorts, we identified known pathogenic STRs in 31 loci using ExpansionHunter. WGS was generated from DNA extracted from blood and brain tissues. We tested the association of STRs with a) neuropathological LOAD status, b) beta‐amyloid levels, c) neurofibrillary tangle (NFT) burden, d) global measure of pathology based on the scaled scores of 5 brain regions and e) estimated slope of global cognition using longitudinal measurements. Regression models adjusting for age, sex and first three principal components. Subsequently, we examined if STRs influenced gene expression in dorsolateral prefrontal cortex (DLPFC), posterior cingulate cortex (PCC) and the anterior cingulate (AC) and tested if the association of STRs with neuropathological traits were mediated by altered gene expression.ResultTGC repeat in ATXN1 was associated with cognitive decline (b = ‐0.007, p = 0.014) and risk of clinical AD (b = 0.126, p = 0.03). Variation in CAG repeats in ATN1 was associated with cognition (b = 0.004, p = 0.022) and risk of pathological AD (b = ‐0.069, p = 0.035). Longer Repeats at ATXN1 increased gene expression in DLPFC (b = 0.012, p = 0.049) and PCC (b = 0.019, p = 0.006) and repeats in ATN1 altered DLPFC (b = 0.01, p = 0.016) and PCC (b = 0.01, p = 0.026) expression. Mediation analysis determined that the effect of the CAG repeats in ATN1 on tau was mediated by gene expression in PCC (p = 0.004).ConclusionWe demonstrate that disease causing STRs influence the underlying gene expression in brain and are associated with neuropathological and cognitive endophenotypes of AD. This suggests that STRs could explain some of the missing heritability in LOAD.