We show that long-read sequencing with a single Oxford Nanopore Technologies PromethION flow cell per individual achieves 30× human genome coverage and enables accurate assessment of tandem repeats including the 10,000-bp Alzheimer's disease-associated ABCA7 VNTR.
Massive parallel sequencing recently allowed the identification of three genes carrying a higher burden of rare, protein-truncating and missense predicted damaging variants in Alzheimer disease (AD) cases as compared to controls: TREM2, SORL1, and ABCA7.
All patients carrying a loss-of-function mutation in ABCA7 exhibited a classical Alzheimer disease phenotype, though with a striking wide onset age range, suggesting the influence of unknown modifying factors.
There were four significant associations between genotypes and phenotypes of AD patients: CR1 SNP rs11803956 correlated with Mini-Mental State Examination (MMSE) score (β=1.718, Pcorrected=0.002); ABCA7 SNP rs3752232 correlated with Rey Complex Figure Test (RCFT) copy score (β=-6.861, Pcorrected=0.013); APOE SNP rs2075650 correlated with the percentile of RCFT copy score (β=14.005, Pcorrected=0.021) and the percentile of total score in phonemic fluency (β=11.052, Pcorrected=0.035).
Several genes associated with AD risk-most notably, the ε4 allele of the apolipoprotein E (APOE) gene and several mutations in the ATP-binding cassette transporter A7 (ABCA7) gene-are linked to altered lipid metabolism, especially in AAs.
Thus, our study suggested that ABCA7 genotypes contribute to the AD risk through involvement in amyloid-β deposition on in vivo imaging, but not in tau pathology, brain atrophy, or decreased glucose metabolism.
Besides the previously reported APOE and CR1 loci, we found that the ABCA7 (rs3764650; P = .02) and CD2AP (rs9349407; P = .03) AD susceptibility loci are associated with neuritic plaque burden.
The effect of loss-of-function mutations on ABCA7 expression was investigated with quantitative real-time PCR in post-mortem brains of patients (n=3) and control individuals (n=4); nonsense mediated mRNA decay was investigated in lymphoblast cell lines from three predicted loss-of-function mutation carriers from the cohort of 772 patients with Alzheimer's disease.
Similarly, the more prevalent late-onset forms of AD are associated with both coding and non-coding variants in genes such as SORL1, PICALM and ABCA7 that affect the production and clearance of Aβ.
To probe for a function of ABCA7 in vivo, we crossed Abca7(-/-) mice with J20 mice, an amyloidogenic transgenic AD mouse model [B6.Cg-Tg(PDGFB-APPSwInd)20Lms/J] expressing a mutant form of human APP bearing both the Swedish (K670N/M671L) and Indiana (V717F) familial AD mutations.
Thus, in African Americans the interactive effects of ABCA7rs3764650 and aerobic fitness likely compound overall ABCA7-related AD risk, and may contribute to health disparities whereby African Americans are at a higher risk for dementia, with double the prevalence of AD.
There are other cis-variants that significantly influence brain expression of CLU and ABCA7 (p = 4.01 × 10(-5)-9.09 × 10(-9)), some of which also associate with AD risk (p = 2.64 × 10(-2)-6.25 × 10(-5)).
The pooled effect of ABCA7rs3764605 allele G was significantly associated with an increased the risk of AD (OR=1.20, 95% CI: 1.14-1.26, P value <0.001).
In total, we identified 78 potentially damaging rare variants (frequency <1%), including ABCA7p.L400V in a family with Alzheimer's disease and LRRK2 p.R1514Q in 6 of 98 patients with Parkinson's disease (6.1%).
An association with the known AD gene ABCA7 was replicated in several ancestries (discovery P=.0049, European P=.041, African American P=.043, and Asian P=.027), suggesting that exonic variants within this gene modify AD susceptibility.
We found that loss-of-function variants in ABCA7 confer risk of Alzheimer's disease in Icelanders (odds ratio (OR) = 2.12, P = 2.2 × 10(-13)) and discovered that the association replicated in study groups from Europe and the United States (combined OR = 2.03, P = 6.8 × 10(-15)).
We investigated the association of Alzheimer's disease (AD)-related rare variants APP A673T and ABCA7rs200538373-C with the levels of β-amyloid (Aβ) and parameters of metabolic and cardiovascular health in a population-based cohort of healthy middle-aged and elderly men.