Alzheimer's Disease Genetics Research Articles

Recruiting African American males in Alzheimer's disease education and genetics research

AbstractBackgroundAddressing the disparity Late Onset Alzheimer’s disease (LOAD) prevalence among African Americans (AA) requires deliberate inclusion of this population in Alzheimer’s disease (AD) studies. Recruiting AA for research studies remains a significant challenge for AD genetic studies. Recruiting and retaining AA males (AAMs) is an even greater challenge, even when study personnel is AA, many traditional recruitment barriers are removed, and community outreach in AA communities is available and culturally appropriate. In this project, we highlight engagement of African American males in outreach and recruitment in three AD studies, and point to the need for expanded and targeted engagement opportunities for this population. While AA males indicate a willingness to participate equal to women, their actual participation is significantly less and may diminish potential generalization of studies in African Americans.MethodWe used culturally relevant approaches to educate and build trust within AA communities and made significant contributions to AA participation in AD genomic studies. For this study, we tracked AAM participation in community engagement activities and enrollment in AD genomic research studies over time.ResultsOver the past 5 years, 22% of the participants surveyed at an annual AA AD conference were AAM. Participation of AAM’s in large genomic studies such as the Research in African American Alzheimer’s Disease Initiative (24%), African American Alzheimer’s Disease study (24%), the largest Genome Wide Association Study, with 5896 total participants (30%), consistently fell below their non‐Hispanic White counterparts. The average participation of NHW males was 41% over the same period.ConclusionWe have used culturally relevant strategies to engage AAMs in education and in genomic research studies. Their participation falls far below their representation in the general population and below their NHW counterparts. Implementing evidence‐based strategies that specifically address trust and gender‐specific needs of AAMs will be important in increasing their participation in genomic studies in AD, and thus generalizability of study results.

Recruitment strategies for the genetics of Alzheimer disease in the Puerto Rican population

AbstractBackgroundWith over 5.1 million individuals, the Puerto Rican population makes up over 1.5% of the US population and is the 2nd largest Hispanic/Latino population in the continental US. There are an estimated of 60,000 cases of AD on the island. The Puerto Rico Alzheimer's and Related Dementias Initiatives (PRADI) cohort will both leverage and complement existing AD Resources, the Alzheimer Disease Sequencing Project (ADSP) with the inclusion of a diverse and underrepresented population. At present, the cohort consists of a total of 935 total participants including individuals from 115 multiplex AD families. There are 418 cases of dementia, 217 mild cognitive impairment, and 300 unrelated and family‐based controls.MethodWe examined the most successful strategy to recruit cases and controls as well as multiplex families for both case/control and family‐based genetic studies. We began by engaging a wide range of stakeholders across the island. The core activities of our team include relationship building, partnership development and maintenance, and coalition building. For the community outreach, we utilize mass media like newspapers, radio interviews, and focal group presentations and engaged the following stakeholder groups: Alzheimer disease day care centers, elderly housing in San Juan, senior day care centers, non‐profit organizations, private neurology offices, and other community‐based organizations such as the Alzheimer’s Association.ResultThe percent of patients recruited through each stakeholder group were 45.76% (428/935) from community outreach, 34.33% (321/935) from private neurologist practices, 18.93% (177/935) from senior day care centers and 0.96% (9/935) from Alzheimer disease day care centers. The mean age and standard deviation of cases and controls were 78.22 years (±9.37) and 70.84 years (±7.92) respectively. Examining the data with respect to multiplex family structure, we found that 53.77% of the families (including the largest families) came from private physician referral.ConclusionPartnering with diverse stakeholders and building coalitions proved to be effective as an outreach method for recruitment. Private physicians remain an excellent source for the identification of multiplex AD families for family‐based genetics study. Outreach community‐based approaches are highly successful mechanisms to educate and engage participants in genetic research.

Mechanism for the protective effect of APOE ε2 against Alzheimer disease is linked to tau and the classical complement pathway

AbstractBackgroundRecent reports suggest that the rare APOE Christchurch mutation and APOE2 allele protect against Alzheimer’s disease (AD) pathology by reducing the burden of tau pathology. However, the mechanism(s) underlying the APOE2 protective effect linking to tau is largely unknown.MethodWe conducted a genome‐wide association study (GWAS) for AD among 2,120 APOE2 carriers from the Alzheimer Disease Genetics Consortium (ADGC), and prioritized by gene network analysis and methylation profiling of CpG sites in the locus using the Religious Orders Study and Memory and Aging Project (ROSMAP) data. We also performed differential gene expression analysis among APOE2/3 subjects in prefrontal cortex tissue from 44 AD and 75 control brains of the Framingham Heart Study (FHS), Boston University Alzheimer’s Disease Center (BUADC), and ROSMAP. We validated the relationships between protein levels of the top‐ranked genes and levels of tau and amyloid beta proteins in prefrontal cortex area of 193 FHS/BUADC brains.ResultOf the significant genetic associations with AD (P < 10−6), PPP2CB was the key node in APOE2‐related gene networks and contained the most significant CpG site (P = 5.2 × 10−4) located 2,814 bp upstream of the top‐ranked GWAS variant. The complement genes C4A and C4B were the top‐ranked differentially expressed genes (P < 2 × 10−4) with reduced expression in APOE2/3 controls compared in APOE2/3 cases or other carriers. Furthermore, the level of PPP2CB protein was significantly associated with increased levels of C4B protein (P = 8.2 × 10−7), and the C4A level was associated with increased pTau231/tTau ratio (P = 0.006). Protein levels of C4A, C4B, and PPP2CB were not associated with amyloid beta 42 (Aβ42) or pTau181/tTau ratio. We were unable to confirm previous reports on the role of C1q, since the C1q level was not associated with any of these phenotypes.ConclusionThis is the first to report the molecular link between a tau phosphatase and the classical complement pathway, especially C4, as a mechanism for the ε2 protective effect against AD. Our findings may lead to the development of novel therapeutic targets for AD by mimicking the neuroprotective effect of APOE2.

How understudied populations leverage our understanding of Alzheimer’s disease genetics

AbstractBackgroundThe majority of genome‐wide association studies have been conducted using samples with a European genetic background. As a field, we acknowledge this limitation and the need to increase the diversity of populations studied. A major challenge when designing and conducting such studies is to assimilate large samples sizes to have enough statistical power to detect variants associated with disease, particularly when trying to identify variants with low and rare minor allele frequencies. In this study, we aimed to illustrate the benefits, to genetic characterization of Alzheimer’s disease (AD), in researching currently understudied populations. This is important for both fair representation of world populations and the translatability of findings.MethodWe have conducted a thorough literature search to understand the contributions of studies, on different populations, to AD genetics.ResultTo accomplish this, we have systematically quantified the number of studies identifying mutations in known disease‐causing genes, in all countries across the world, and discussed the contributions of research in understudied populations to the identification of novel genetic factors in this disease. Related to this, we compared the varied effects of genome‐wide significant SNPs across populations by focusing on loci that show different association profiles between populations (a key example being APOE).ConclusionThis work functions to both highlight how understudied populations have furthered our understanding of AD genetics, and to help us gage our progress on understanding the genetic architecture of this disease in all populations.

NIA genetics of Alzheimer’s disease data storage site (NIAGADS): Update 2020

AbstractBackgroundNIAGADS is a national genetics data repository that facilitates access of genotypic data to qualified investigators for the study of the genetics of late‐onset Alzheimer’s disease (AD) and other neurological diseases. Collaborations with large consortia and centers such as the Alzheimer’s Disease Genetics Consortium (ADGC), Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Consortium, the Alzheimer’s Disease Genome Sequencing Project (ADSP), and the Genome Center for Alzheimer’s Disease (GCAD) allow NIAGADS to lead the effort in managing large AD datasets that can be easily accessed by the research community and utilized to their fullest extent.MethodNIAGADS is supported by National Institute on Aging (NIA) under a cooperative agreement (U24 AG041689). All data derived from NIA funded AD genetics studies are expected to be deposited in NIAGADS or another NIA approved site. NIAGADS manages a Data Sharing Service (DSS) that facilitates the deposition and sharing of genomic data and association results with approved users in the neurodegenerative research community. In addition, researchers are able to freely use the NIAGADS Genomics Database to search annotation resources that link published AD studies to AD‐relevant sequence features and genome‐wide annotations.ResultAs of January 2020, NIAGADS houses 67 datasets (23 added in 2019) with >59,000 samples and nearly 34 billion genotypes. Qualified investigators can retrieve ADSP sequencing data with ease and flexibility through the NIAGADS DSS. The ADSP and other contributing studies have completed whole exome sequencing (WES) of 20,630 subjects and whole‐genome sequencing (WGS) of 4,750 subjects. Raw WES and WGS files, quality controlled VCF files, and phenotype data files are available via qualified access. The next planned dataset release will occur in late 2020 and will contain an additional 13,136 genomes jointly genotype called with the first release of 4,750 genomes, totaling about 17,886 genomes.ConclusionNIAGADS is a rich resource for AD researchers, with the goal of facilitating advances in Alzheimer’s genetics research. By housing datasets from multiple projects and institutions, NIAGADS enables AD researchers to be more efficient in meeting their research goals. Datasets, guidelines, and new features are available on our website at https://www.niagads.org.

Association of Uncommon, Noncoding Variants in the APOE Region With Risk of Alzheimer Disease in Adults of European Ancestry

The ε2 and ε4 alleles of the apolipoprotein E (APOE) gene are associated with Alzheimer disease (AD) risk. Although nearby genetic variants have also been shown to be associated with AD, including rs2075650 in the TOMM40 gene and rs4420638 near the APOC1 gene, it is unknown whether these associations are independent of the ε2 and ε4 alleles. To assess whether variants near APOE are associated with AD independently of the ε2/ε3/ε4 genotype. In this genetic association study of the Alzheimer's Disease Genetics Consortium imputed genotype at data, 14 415 variants near APOE (±500 kilobase) for 18 795 individuals with European ancestry were tested for association with AD using 4 logistic mixed models adjusting for sex, cohort, population structure, and relatedness. Model 1 had no APOE adjustment, and model 2 adjusted for the count of ε2 and ε4 alleles. Model 3 was restricted to ε3 homozygotes, and model 4 was restricted to ε4 homozygotes. Data were downloaded from May 31, 2018, to June 3, 2018, and analyzed from November 1, 2018, to June 24, 2020. Alzheimer disease affectation status was defined by clinicians using standard National Institute of Neurological and Communicative Disorders and Stroke and Alzheimer Disease and Related Disorders Association criteria. Association was evaluated using Score tests; results with P < .05 divided by the number of independent tests per model were considered statistically significant. Among the 18 795 individuals in the study, 9704 were affected by AD and 9066 were control individuals; the median age at onset/evaluation was 76 (interquartile range, 70-82) years; and 11 167 were female (59.4%). Associations with AD were found for rs2075650 (odds ratio [OR], 2.59; 95% CI, 2.45-2.75; P = 3.19 × 10-228) and rs4420638 (OR, 2.77; 95% CI, 2.62-2.94; P = 2.99 × 10-254) without APOE adjustment. Although rs2075650 was nominally associated with AD among the ε4 homozygotes (OR, 1.33; 95% CI, 1.00-1.77; P = .047), the association between rs4420638 and AD was eliminated by APOE adjustment (model 2 OR, 1.06 [95% CI, 0.96-1.18; P = .24]; model 3 OR, 1.13 [95% CI, 0.95-1.34; P = .18]; model 4 OR, 0.90 [95% CI, 0.56-1.45; P = .66]). There was a significant association between rs192879175 and AD among ε3 homozygotes (OR, 0.50; 95% CI, 0.37-0.68; P = 8.30 × 10-6). The results of this genetic association study suggest that ε2/ε3/ε4 alleles are not the only variants in the APOE region that are associated with AD risk. Additional work with independent data is needed to replicate these results.

Novel Alzheimer Disease Risk Loci and Pathways in African American Individuals Using the African Genome Resources Panel

Compared with non-Hispanic White individuals, African American individuals from the same community are approximately twice as likely to develop Alzheimer disease. Despite this disparity, the largest Alzheimer disease genome-wide association studies to date have been conducted in non-Hispanic White individuals. In the largest association analyses of Alzheimer disease in African American individuals, ABCA7, TREM2, and an intergenic locus at 5q35 were previously implicated. To identify additional risk loci in African American individuals by increasing the sample size and using the African Genome Resource panel. This genome-wide association meta-analysis used case-control and family-based data sets from the Alzheimer Disease Genetics Consortium. There were multiple recruitment sites throughout the United States that included individuals with Alzheimer disease and controls of African American ancestry. Analysis began October 2018 and ended September 2019. Diagnosis of Alzheimer disease. A total of 2784 individuals with Alzheimer disease (1944 female [69.8%]) and 5222 controls (3743 female [71.7%]) were analyzed (mean [SD] age at last evaluation, 74.2 [13.6] years). Associations with 4 novel common loci centered near the intracellular glycoprotein trafficking gene EDEM1 (3p26; P = 8.9 × 10-7), near the immune response gene ALCAM (3q13; P = 9.3 × 10-7), within GPC6 (13q31; P = 4.1 × 10-7), a gene critical for recruitment of glutamatergic receptors to the neuronal membrane, and within VRK3 (19q13.33; P = 3.5 × 10-7), a gene involved in glutamate neurotoxicity, were identified. In addition, several loci associated with rare variants, including a genome-wide significant intergenic locus near IGF1R at 15q26 (P = 1.7 × 10-9) and 6 additional loci with suggestive significance (P ≤ 5 × 10-7) such as API5 at 11p12 (P = 8.8 × 10-8) and RBFOX1 at 16p13 (P = 5.4 × 10-7) were identified. Gene expression data from brain tissue demonstrate association of ALCAM, ARAP1, GPC6, and RBFOX1 with brain β-amyloid load. Of 25 known loci associated with Alzheimer disease in non-Hispanic White individuals, only APOE, ABCA7, TREM2, BIN1, CD2AP, FERMT2, and WWOX were implicated at a nominal significance level or stronger in African American individuals. Pathway analyses strongly support the notion that immunity, lipid processing, and intracellular trafficking pathways underlying Alzheimer disease in African American individuals overlap with those observed in non-Hispanic White individuals. A new pathway emerging from these analyses is the kidney system, suggesting a novel mechanism for Alzheimer disease that needs further exploration. While the major pathways involved in Alzheimer disease etiology in African American individuals are similar to those in non-Hispanic White individuals, the disease-associated loci within these pathways differ.

107 - New trends in aging and dementia in Latin America and the Caribbean Region

Alzheimer’s disease (AD) and dementia has emerged as a significant societal issue and a global priority. The prevalence of dementia is rising more rapidly in low and middle income countries (LMIC) than in high income countries. Yet, knowledge of dementia risk factors is dominated by research from high income countries (HIC), which cannot be readily translated to LMIC. Latin American countries (LAC) have unique challenges related to dementia, including rapid aging population, high admixture degree and risk factors profile, which influence the prevalence and presentation of dementia. Several epidemiological studies during the past decade have shown a rapid increase of dementia in LAC, but the impact of genetic, protective and risk factors remain poorly understood. This research session will feature a series of short and engaging talks about new trends of dementia in the region and will answer key questions regarding dementia determinants and consequences in Hispanic populations. Participants will be first introduced to the aging process in LAC, prevalence and incidence of dementia within the region. The second presentation will report on genetics of Alzheimer disease in Hispanic populations. The third presenter will discuss the complexities of dementia multimorbidity and the impact of neuropsychiatric symptoms. The fourth presenter will discuss about Nationals and Regional Strategies to address dementia and reflects on recommendations and future directions for the region. All presentations will be based on findings from multiple research projects across the region. Furthermore, presenters will extended comparison to Non-Hispanics whites and Hispanics populations living in US, which allows cross countries/society comparisons. Overall, new information about dementia will be shared with the audience. Attendees will be able to identify the unique genetic and social determinants that drive AD in LAC. Recommendations will be given for preventive strategies tailored to LMIC. The findings to be shared will be essential for building evidence-based interventions that achieve the goals of the National Plan to Address Alzheimer’s Disease.

Alzheimer Gene BIN1 may Simultaneously Influence Dementia Risk and Androgen Deprivation Therapy Dosage in Prostate Cancer.

Androgen deprivation therapy (ADT) is extensively used in prostate cancer. Yet the risk of impaired cognition or Alzheimer disease (AD) in men with prostate cancer receiving ADT is uncertain. Some studies of prostate cancer and ADT suggest that the risk of AD is not increased. But other studies have found an increased risk of AD and cognitive impairment. As the uncertainty about ADT and dementia might relate to the genetics of prostate cancer and AD, the authors used the Cancer Genome Atlas (TCGA) to examine the relationship in men with prostate cancer between genes implicated in AD and genes implicated in prostate cancer. The authors examined the genomics of 492 prostate cancer cases in the Genomic Data Commons (GDC) TCGA Prostate Cancer (PRAD) data set. To access and analyze the data, 2 web-based interfaces were used: (1) the UCSC Xena browser, a web-based visual integration and exploration tool for TCGA data, including clinical and phenotypic annotations; and (2) cBioportal, a web-based interface that enables integrative analysis of complex cancer genomics and clinical profiles. Co-occurrence analysis indicates that alterations in the prostate cancer gene Speckle-type POZ protein (SPOP) significantly co-occur with alterations in the AD gene BIN1 (P<0.001). The presence of somatic mutations (deleterious and missense/in frame) in SPOP deranges BIN1 gene expression. SPOP/BIN1 RNA gene expression in 492 prostate cancer specimens is significantly correlated (P<0.001). Increased expression of SPOP in 492 prostate cancers is associated with reduced survival (P=0.00275). Men receiving pharmacologic therapy had a tumor with a significantly higher Gleason score (P=0.023). Gleason score and BIN1 RNA gene expression, unit log2 (fragments per kilobase of transcript per million mapped reads upper quartile [FPKM-UQ]+1), in 499 prostate cancer specimens were significantly inversely correlated (P<0.001). BIN1 forms part of a network that interacts with the MYC oncogene, activated at the earliest phases of prostate cancer and in its position on chr8q24 linked to disease aggressiveness. Dynamic regulation of the BIN1-Tau interaction is involved in AD. BIN1 loss in AD allows phosphorylated tau to be mis-sorted to synapses, which likely alters the integrity of the postsynapse, alongside reducing the functionally important release of physiological forms of tau. Alzheimer symptoms are usually preceded by a preclinical phase that may be 16 years long. The authors suggest that the ADT dosage reflects the severity of a process that is already underway. The severity is determined by the genetics of the tumor itself, at least in part by BIN1. ADT is not causing new cases of AD. The oncologist treats higher-grade prostate cancer with more ADT, which serves as a surrogate marker for disease severity. Our analysis of TCGA data does not support the idea that ADT causes AD or dementia.

MAPT haplotype-stratified GWAS reveals differential association for AD risk variants.

Introduction MAPT H1 haplotype is implicated as a risk factor for neurodegenerative diseases including Alzheimer's disease (AD).MethodsUsing Alzheimer's Disease Genetics Consortium (ADGC) genome‐wide association study (GWAS) data (n = 18,841), we conducted a MAPT H1/H2 haplotype–stratified association to discover MAPT haplotype–specific AD risk loci.ResultsWe identified 11 loci—5 in H2‐non‐carriers and 6 in H2‐carriers—although none of the MAPT haplotype–specific associations achieved genome‐wide significance. The most significant H2 non‐carrier–specific association was with a NECTIN2 intronic (P = 1.33E‐07) variant, and that for H2 carriers was near NKX6‐1 (P = 1.99E‐06). The GABRG2 locus had the strongest epistasis with MAPT H1/H2 variant rs8070723 (P = 3.91E‐06). Eight of the 12 genes at these loci had transcriptome‐wide significant differential expression in AD versus control temporal cortex (q < 0.05). Six genes were members of the brain transcriptional co‐expression network implicated in “synaptic transmission” (P = 9.85E‐59), which is also enriched for neuronal genes (P = 1.0E‐164), including MAPT.DiscussionThis stratified GWAS identified loci that may confer AD risk in a MAPT haplotype–specific manner. This approach may preferentially enrich for neuronal genes implicated in synaptic transmission.

CHARACTERIZING THE PROPAGATION PATTERN OF NEURODEGENERATION IN ALZHEIMER'S DISEASE BY LONGITUDINAL NETWORK ANALYSIS.

Converging evidence shows that Alzheimer's disease (AD) is a neurodegenerative disease that represents a disconnection syndrome, whereby a large-scale brain network is progressively disrupted by one or more neuropathological processes. However, the mechanism by which pathological entities spread across a brain network is largely unknown. Since pathological burden may propagate trans-neuronally, we propose to characterize the propagation pattern of neuropathological events spreading across relevant brain networks that are regulated by the organization of the network. Specifically, we present a novel mixed-effect model to quantify the relationship between longitudinal network alterations and neuropathological events observed at specific brain regions, whereby the topological distance to hub nodes, high-risk AD genetics, and environmental factors (such as education) are considered as predictor variables. Similar to many cross-section studies, we find that AD-related neuropathology preferentially affects hub nodes. Furthermore, our statistical model provides strong evidence that abnormal neuropathological burden diffuses from hub nodes to non-hub nodes in a prion-like manner, whereby the propagation pattern follows the intrinsic organization of the large-scale brain network.

The MUC6/AP2A2 Locus and Its Relevance toAlzheimer's Disease: A Review.

We recently reported evidence of Alzheimer’s disease (AD)-linked genetic variation within the mucin 6 (MUC6) gene on chromosome 11p, nearby the adaptor-related protein complex 2 subunit alpha 2 (AP2A2) gene. This locus has interesting features related to human genomics and clinical research. MUC6 gene variants have been reported to potentially influence viral—including herpesvirus—immunity and the gut microbiome. Within the MUC6 gene is a unique variable number of tandem repeat (VNTR) region. We discovered an association between MUC6 VNTR repeat expansion and AD pathologic severity, particularly tau proteinopathy. Here, we review the relevant literature. The AD-linked VNTR polymorphism may also influence AP2A2 gene expression. AP2A2 encodes a polypeptide component of the adaptor protein complex, AP-2, which is involved in clathrin-coated vesicle function and was previously implicated in AD pathogenesis. To provide background information, we describe some key knowledge gaps in AD genetics research. The “missing/hidden heritability problem” of AD is highlighted. Extensive portions of the human genome, including the MUC6 VNTR, have not been thoroughly evaluated due to limitations of existing high-throughput sequencing technology. We present and discuss additional data, along with cautionary considerations, relevant to the hypothesis that MUC6 repeat expansion influences AD pathogenesis.

Failure to detect synergy between variants in transferrin and hemochromatosis and Alzheimer's disease in large cohort

Alzheimer's disease (AD) is the most common cause of dementia and, despite decades of effort, there is no effective treatment. In the last decade, many association studies have identified genetic markers that are associated with AD status. Two of these studies suggest that an epistatic interaction between variants rs1049296 in the transferrin (TF) gene and rs1800562 in the homeostatic iron regulator (HFE) gene, commonly known as hemochromatosis, is in genetic association with AD. TF and HFE are involved in the transport and regulation of iron in the brain, and disrupting these processes exacerbates AD pathology through increased neurodegeneration and oxidative stress. However, by using a significantly larger data set from the Alzheimer's Disease Genetics Consortium, we fail to detect an association between TF rs1049296 or HFE rs1800562 with AD risk (TF rs1049296 p = 0.38 and HFE rs1800562 p = 0.40). In addition, logistic regression with an interaction term and a synergy factor analysis both failed to detect epistasis between TF rs1049296 and HFE rs1800562 (SF = 0.94; p = 0.48) in AD cases. Each of these analyses had sufficient statistical power (power > 0.99), suggesting that previously reported associations may be the result of more complex epistatic interactions, genetic heterogeneity, or false-positive associations because of limited sample sizes.

Genetics of Alzheimer's disease: where we are, and where we are going.

Alzheimer's disease (AD) has a very strong genetic component, whose characterization has become an essential part of efforts to understand the pathophysiological processes of the disease. Thanks to the systematic use of high-throughput approaches over the last 10 years, more than 40 genes/loci have been linked to the AD risk. Although some of these signals are likely to be false positives, this genetic knowledge has shed new light on the pathogenesis of AD and, in particular, the major role of microglia. However, our knowledge of the genetics of AD is far from complete, and larger and more diverse genetic studies are required. Lastly, post-GWAS analyses will be needed to make sense of this genetic information without focusing too much on what we think we know about the disease.

Genetic Analysis of Alzheimer's Disease: The Impact of Rare Variants and Their Significance

Next generation sequencing (NGS) technology has dramatically influenced the field of omics studies, such as genomics and transcriptomics. It is now possible to access a significant number of previously known and novel genomic variants through NGS. Although the effective manipulation and accurate interpretation of the inordinate amount of data may pose a considerable challenge, it enables us to identify specific genes responsible for causing or influencing the susceptibility to a plethora of diseases. Alzheimer's disease (AD) is the most common etiology of dementia in the elderly (approximately 60-70%). The current research trend of AD genetics focuses on the analysis of rare variants (allelic frequency <1%) instead of common variants (allelic frequency >1%) to identify AD-associated genes/variants. A number of genes (such as TREM2, ABCA7, SORL1) that carry rare pathogenic variants have reportedly conferred susceptibility to AD with stronger genetic risk effects (odds ratio >2.0). Here, we are going to introduce a small part of the latest many attractive findings about AD genetic researches.

IDENTIFICATION OF GENES MODIFYING AGE-AT-ONSET OF ALZHEIMER’S DISEASE IN THE ALZHEIMER’S DISEASE GENETICS CONSORTIUM (ADGC) COHORTS

The Alzheimer Disease Genetics Consortium (ADGC) has previously conducted a genome-wide association study for age-at-onset (AAO) of Alzheimer disease (AD) (Naj et al. 2014) that identified several associated variants in known risk genes as well as novel AAO variants. Here we re-examine AAO in the ADGC dataset with additional cohorts and improved genome-wide imputation. A total 6642 unrelated AD cases with AAO data from 20 ADGC cohorts were investigated. Imputation was performed for each dataset based on Haplotype Reference Consortium (HRC) reference panel at Michigan Imputation Server. Consistent quality control procedures were applied to each dataset separately. In each dataset, multivariable linear regression was used to test the association between genotypes at each variant (with minor allele count >5) and AAO, with covariate adjustment for sex and the first 3 PCs. Meta-analysis with the METAL program was performed across the 20 cohorts. Genome-wide statistical significance was defined at p< 5x10−8, and all variants with at least p< 10−5 were examined. The average AAO ranged from 72.2 to 86.1 years among AD cases in the 20 datasets. A total of 45 variants in 12 different regions were associated with AAO showing p<10−5 in the meta-analysis. Genome-wide significance associations were observed for 14 variants in the chromosome 19 APOE region. An additional 11 candidate loci were identified with associations of p<10−5 including SLC30A6 (p=1.83x10−6), a known risk gene with altered expression in AD brain plaques, and the SORCS1 gene (p=8.63x10−6) located in a chromosome 10q linkage region previously reported for AAO of AD (Li et al. 2002). Two of the candidate loci on chromosomes 5 and 19 overlap signals reported in Naj et al. (2014), while 10 were not previously identified. Using the densest and highest quality imputation to date, we replicated associations in the APOE region with AAO of AD and identified several candidate genes not previously found to affect AD risk. Our study shows that additional genetic contributors to AD can be identified through analysis of AAO.

Alzheimer Disease Pathogenesis: Insights From Molecular and Cellular Biology Studies of Oligomeric Aβ and Tau Species.

Alzheimer disease (AD) represents an oncoming epidemic that without an effective treatment promises to exact extraordinary human and financial burdens. Studies of pathogenesis are essential for defining targets for discovering disease-modifying treatments. Past studies of AD neuropathology provided valuable, albeit limited, insights. Nevertheless, building on these findings, recent studies have provided an increasingly rich harvest of genetic, molecular and cellular data that are creating unprecedented opportunities to both understand and treat AD. Among the most significant are those documenting the presence within the AD brain of toxic oligomeric species of Aβ and tau. Existing data support the view that such species can propagate and spread within neural circuits. To place these findings in context we first review the genetics and neuropathology of AD, including AD in Down syndrome (AD-DS). We detail studies that support the existence of toxic oligomeric species while noting the significant unanswered questions concerning their precise structures, the means by which they spread and undergo amplification and how they induce neuronal dysfunction and degeneration. We conclude by offering a speculative synthesis for how oligomers of Aβ and tau initiate and drive pathogenesis. While 100 years after Alzheimer’s first report there is much still to learn about pathogenesis and the discovery of disease-modifying treatments, the application of new concepts and sophisticated new tools are poised to deliver important advances for combatting AD.

CpG-related SNPs in the MS4A region have a dose-dependent effect on risk of late-onset Alzheimer disease.

CpG‐related single nucleotide polymorphisms (CGS) have the potential to perturb DNA methylation; however, their effects on Alzheimer disease (AD) risk have not been evaluated systematically. We conducted a genome‐wide association study using a sliding‐window approach to measure the combined effects of CGSes on AD risk in a discovery sample of 24 European ancestry cohorts (12,181 cases, 12,601 controls) from the Alzheimer's Disease Genetics Consortium (ADGC) and replication sample of seven European ancestry cohorts (7,554 cases, 27,382 controls) from the International Genomics of Alzheimer's Project (IGAP). The potential functional relevance of significant associations was evaluated by analysis of methylation and expression levels in brain tissue of the Religious Orders Study and the Rush Memory and Aging Project (ROSMAP), and in whole blood of Framingham Heart Study participants (FHS). Genome‐wide significant (p < 5 × 10−8) associations were identified with 171 1.0 kb‐length windows spanning 932 kb in the APOE region (top p < 2.2 × 10−308), five windows at BIN1 (top p = 1.3 × 10−13), two windows at MS4A6A (top p = 2.7 × 10−10), two windows near MS4A4A (top p = 6.4 × 10−10), and one window at PICALM (p = 6.3 × 10‐9). The total number of CGS‐derived CpG dinucleotides in the window near MS4A4A was associated with AD risk (p = 2.67 × 10−10), brain DNA methylation (p = 2.15 × 10−10), and gene expression in brain (p = 0.03) and blood (p = 2.53 × 10−4). Pathway analysis of the genes responsive to changes in the methylation quantitative trait locus signal at MS4A4A (cg14750746) showed an enrichment of methyltransferase functions. We confirm the importance of CGS in AD and the potential for creating a functional CpG dosage‐derived genetic score to predict AD risk.

Curcumin restores innate immune Alzheimer's disease risk gene expression to ameliorate Alzheimer pathogenesis.

Alzheimer's disease (AD) genetics implies a causal role for innate immune genes, TREM2 and CD33, products that oppose each other in the downstream Syk tyrosine kinase pathway, activating microglial phagocytosis of amyloid (Aβ). We report effects of low (Curc-lo) and high (Curc-hi) doses of curcumin on neuroinflammation in APPsw transgenic mice. Results showed that Curc-lo decreased CD33 and increased TREM2 expression (predicted to decrease AD risk) and also increased TyroBP, which controls a neuroinflammatory gene network implicated in AD as well as phagocytosis markers CD68 and Arg1. Curc-lo coordinately restored tightly correlated relationships between these genes' expression levels, and decreased expression of genes characteristic of toxic pro-inflammatory M1 microglia (CD11b, iNOS, COX-2, IL1β). In contrast, very high dose curcumin did not show these effects, failed to clear amyloid plaques, and dysregulated gene expression relationships. Curc-lo stimulated microglial migration to and phagocytosis of amyloid plaques both in vivo and in ex vivo assays of sections of human AD brain and of mouse brain. Curcumin also reduced levels of miR-155, a micro-RNA reported to drive a neurodegenerative microglial phenotype. In conditions without amyloid (human microglial cells in vitro, aged wild-type mice), Curc-lo similarly decreased CD33 and increased TREM2. Like curcumin, anti-Aβ antibody (also reported to engage the Syk pathway, increase CD68, and decrease amyloid burden in human and mouse brain) increased TREM2 in APPsw mice and decreased amyloid in human AD sections ex vivo. We conclude that curcumin is an immunomodulatory treatment capable of emulating anti-Aβ vaccine in stimulating phagocytic clearance of amyloid by reducing CD33 and increasing TREM2 and TyroBP, while restoring neuroinflammatory networks implicated in neurodegenerative diseases.

Identification of genetic heterogeneity of Alzheimer's disease across age

The risk of APOE for Alzheimer's disease (AD) is modified by age. Beyond APOE, the polygenic architecture may also be heterogeneous across age. We aim to investigate age-related genetic heterogeneity of AD and identify genomic loci with differential effects across age. Stratified gene-based genome-wide association studies and polygenic variation analyses were performed in the younger (60–79 years, N = 14,895) and older (≥80 years, N = 6559) age-at-onset groups using Alzheimer's Disease Genetics Consortium data. We showed a moderate genetic correlation (rg = 0.64) between the two age groups, supporting genetic heterogeneity. Heritability explained by variants on chromosome 19 (harboring APOE) was significantly larger in younger than in older onset group (p < 0.05). APOE region, BIN1, OR2S2, MS4A4E, and PICALM were identified at the gene-based genome-wide significance (p < 2.73 × 10−6) with larger effects at younger age (except MS4A4E). For the novel gene OR2S2, we further performed leave-one-out analyses, which showed consistent effects across subsamples. Our results suggest using genetically more homogeneous individuals may help detect additional susceptible loci.