Epistasis analysis links immune cascades and cerebral amyloidosis.

TitleEpistasis analysis links immune cascades and cerebral amyloidosis.
Publication TypeJournal Article
Year of Publication2015
AuthorsBenedet AL, Labbe A, Lemay P, Zimmer ER, Pascoal TA, Leuzy A, Mathotaarachchi S, Mohades S, Shin M, Dionne-Laporte A, Beaudry T, Picard C, Gauthier S, Poirier J, Rouleau G, Rosa-Neto P
Corporate AuthorsAlzheimer’s Disease Neuroimaging Initiative
JournalJ Neuroinflammation
Date Published2015 Dec 01
KeywordsAged, Aged, 80 and over, Alzheimer Disease, Amyloidosis, Cognitive Dysfunction, Epistasis, Genetic, Female, Humans, Male, Middle Aged

BACKGROUND: Several lines of evidence suggest the involvement of neuroinflammatory changes in Alzheimer's disease (AD) pathophysiology such as amyloidosis and neurodegeneration. In fact, genome-wide association studies (GWAS) have shown a link between genes involved in neuroinflammation and AD. In order to further investigate whether interactions between candidate genetic variances coding for neuroinflammatory molecules are associated with brain amyloid β (Aβ) fibrillary accumulation, we conducted an epistasis analysis on a pool of genes associated with molecular mediators of inflammation.METHODS: [(18)F]Florbetapir positron emission tomography (PET) imaging was employed to assess brain Aβ levels in 417 participants from ADNI-GO/2 and posteriorly 174 from ADNI-1. IL-1β, IL4, IL6, IL6r, IL10, IL12, IL18, C5, and C9 genes were chosen based on previous studies conducted in AD patients. Using the [(18)F]florbetapir standardized uptake value ratio (SUVR) as a quantitative measure of fibrillary Aβ, epistasis analyses were performed between two sets of markers of immune-related genes using gender, diagnosis, and apolipoprotein E (APOE) as covariates. Voxel-based analyses were also conducted. The results were corrected for multiple comparison tests. Cerebrospinal fluid (CSF) Aβ1-42/phosphorylated tau (p-tau) ratio concentrations were used to confirm such associations.RESULTS: Epistasis analysis unveiled two significant single nucleotide polymorphism (SNP)-SNP interactions (false discovery rate (FDR) threshold 0.1), both interactions between C9 gene (rs261752) and IL6r gene (rs4240872, rs7514452). In a combined sample, the interactions were confirmed (p ≤ 10-5) and associated with amyloid accumulation within cognitively normal and AD spectrum groups. Voxel-based analysis corroborated initial findings. CSF biomarker (Aβ1-42/p-tau) confirmed the genetic interaction. Additionally, rs4240872 and rs7514452 SNPs were shown to be associated with CSF and plasma concentrations of IL6r protein.CONCLUSIONS: Certain allele combinations involving IL6r and C9 genes are associated with Aβ burden in the brain. Hypothesis-driven search for epistasis is a valuable strategy for investigating imaging endophenotypes in complex neurodegenerative diseases.

Alternate JournalJ Neuroinflammation
PubMed ID26626881
PubMed Central IDPMC4666175
Grant ListU01 AG024904 / AG / NIA NIH HHS / United States
MOP-11-51-31 / / Canadian Institutes of Health Research / Canada