Influence of coding variability in APP-Aβ metabolism genes in sporadic Alzheimer's disease

C Sassi, PG Ridge, MA Nalls, R Gibbs, J Ding… - PLoS …, 2016 - journals.plos.org
C Sassi, PG Ridge, MA Nalls, R Gibbs, J Ding, MK Lupton, C Troakes, K Lunnon, S Al-Sarraj…
PLoS One, 2016journals.plos.org
The cerebral deposition of Aβ42, a neurotoxic proteolytic derivate of amyloid precursor
protein (APP), is a central event in Alzheimer's disease (AD)(Amyloid hypothesis). Given the
key role of APP-Aβ metabolism in AD pathogenesis, we selected 29 genes involved in APP
processing, Aβ degradation and clearance. We then used exome and genome sequencing
to investigate the single independent (single-variant association test) and cumulative (gene-
based association test) effect of coding variants in these genes as potential susceptibility …
The cerebral deposition of Aβ42, a neurotoxic proteolytic derivate of amyloid precursor protein (APP), is a central event in Alzheimer’s disease (AD)(Amyloid hypothesis). Given the key role of APP-Aβ metabolism in AD pathogenesis, we selected 29 genes involved in APP processing, Aβ degradation and clearance. We then used exome and genome sequencing to investigate the single independent (single-variant association test) and cumulative (gene-based association test) effect of coding variants in these genes as potential susceptibility factors for AD, in a cohort composed of 332 sporadic and mainly late-onset AD cases and 676 elderly controls from North America and the UK. Our study shows that common coding variability in these genes does not play a major role for the disease development. In the single-variant association analysis, the main hits, none of which statistically significant after multiple testing correction (1.9e-4<p-value<0.05), were found to be rare coding variants (0.009%<MAF<1.4%) with moderate to strong effect size (1.84<OR<Inf) that map to genes mainly involved in Aβ extracellular degradation (TTR, ACE), clearance (LRP1) and APP trafficking and recycling (SORL1). These results were partially replicated in the gene-based analysis (c-alpha and SKAT tests), that reports ECE1, LYZ and TTR as nominally associated to AD (1.7e-3 <p-value <0.05). In concert with previous studies, we suggest that 1) common coding variability in APP-Aβ genes is not a critical factor for AD development and 2) Aβ degradation and clearance, rather than Aβ production, may play a key role in the etiology of sporadic AD.
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