CLU rs9331888 Polymorphism Contributes to Alzheimer's Disease Susceptibility in Caucasian But Not East Asian Populations

Knowledge domains and emerging trends of Genome-wide association studies in Alzheimer's disease: A bibliometric analysis and visualization study from 2002 to 2022

OBJECTIVES

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive decline in cognitive and behavioral function. Studies have shown that genetic factors are one of the main causes of AD risk. genome-wide association study (GWAS), as a novel and effective tool for studying the genetic risk of diseases, has attracted attention from researchers in recent years and a large number of studies have been conducted. This study aims to summarize the literature on GWAS in AD by bibliometric methods, analyze the current status, research hotspots and future trends in this field.

METHODS

We retrieved articles on GWAS in AD published between 2002 and 2022 from Web of Science. CiteSpace and VOSviewer software were applied to analyze the articles for the number of articles published, countries/regions and institutions of publication, authors and cited authors, highly cited literature, and research hotspots.

RESULTS

We retrieved a total of 2,751 articles. The United States had the highest number of publications in this field, and Columbia University was the institution with the most published articles. The identification of AD-related susceptibility genes and their effects on AD is one of the current research hotspots. Numerous risk genes have been identified, among which APOE, CLU, CD2AP, CD33, EPHA1, PICALM, CR1, ABCA7 and TREM2 are the current genes of interest. In addition, risk prediction for AD and research on other related diseases are also popular research directions in this field.

CONCLUSION

This study conducted a comprehensive analysis of GWAS in AD and identified the current research hotspots and research trends. In addition, we also pointed out the shortcomings of current research and suggested future research directions. This study can provide researchers with information about the knowledge structure and emerging trends in the field of GWAS in AD and provide guidance for future research.

Association Between Insulin-like Growth Factor-1 rs35767 Polymorphism and Type 2 Diabetes Mellitus Susceptibility: A Meta-Analysis

Background: Insulin-like growth factor-1 (IGF-1) has been demonstrated to increase fatty acid β oxidation during fasting, and play an important role in regulating lipid metabolism and type 2 diabetes mellitus (T2DM). The rs35767 (T > C) polymorphism, a functional SNP was found in IGF-1 promoter, which may directly affect IGF-1 expression. However, the inconsistent findings showed on the IGF-1 rs35767 polymorphism and T2DM risk.

Methods: We performed a comprehensive meta-analysis to estimate the association between the IGF-1 rs35767 and T2DM risk among four genetic models (the allele, additive, recessive and dominant models).

Results: A total 49,587 T2DM cases and 97,906 NDM controls were included in the allele model, a total 2256 T2DM cases and 2228 NDM controls were included in the other three genetic models (the additive; recessive and dominant models). In overall analysis, the IGF-1 rs35767 was shown to be significantly associated with increased T2DM risk for the allele model (T vs. C: OR = 1.251, 95% CI: 1.082–1.447, p = 0.002), additive model (homozygote comparisons: TT vs. CC: OR = 2.433, 95% CI: 1.095–5.405, p = 0.029; heterozygote comparisons: TC vs. CC: OR = 1.623, 95% CI: 1.055–2.495, p = 0.027) and dominant model (TT + CT vs. CC: OR = 1.934, 95% CI: 1.148–3.257, p = 0.013) with random effects model. After omitting Gouda’s study could reduce the heterogeneity, especially in the recessive model (TT vs. CC + CT: I² = 38.7%, p = 0.163), the fixed effects model for recessive effect of the T allele (TT vs. CC + CT) produce results that were of borderline statistical significance (OR = 1.206, 95% CI: 1.004–1.448, p = 0.045). And increasing the risk of T2DM in Uyghur population of subgroup for the allele model.

Conclusion: The initial analyses that included all studies showed statistically significant associations between the rs35767 SNP and type 2 diabetes, but after removing the Gouda et al. study produced results that were mostly not statistically significant. Therefore, there is not enough evidence from the results of the meta-analysis to indicate that the rs35767 SNP has a statistically significant association with type 2 diabetes.

The 10-Repeat 3'-UTR VNTR Polymorphism in the SLC6A3 Gene May Confer Protection Against Parkinson's Disease: A Meta-analysis

The dopamine transporter (DAT) is encoded by the SLC6A3 gene and plays an important role in the regulation of the neurotransmitter dopamine. The SLC6A3 gene contains several repetition alleles (3-11 repeats) of a 40-base pair variable number of tandem repeats (VNTR) in the 3'-untranslated region (3'-UTR), which may affect DAT expression levels. The 10-repeat (10R) allele could play a protective role against PD. However, inconsistent findings have been reported. Methods: A comprehensive meta-analysis was performed to accurately estimate the association between the 10R allele of the 3'-UTR VNTR in SLC6A3 and PD among four different genetic models. Results: This meta-analysis included a total of 3,142 patients and 3,496 controls. We observed a significant difference between patients and controls for the allele model (10R vs. all others: OR = 0.860, 95% CI: 0.771-0.958, P = 0.006), pseudodominant model (10R/10R + 10R/9R vs. all others: OR = 0.781, 95% CI: 0.641-0.952, P = 0.014) and pseudorecessive model (10R/10R vs. all others: OR = 0.858, 95% CI: 0.760-0.969, P = 0.013) using a fixed effects model. No significant differences were observed under the pseudocodominant model (10R/9R vs. all others: OR = 1.079, 95% CI: 0.945-1.233, P = 0.262). By subgroup analysis, the 10R, 10R/10R and 10R/9R genotypes were found to be significantly different from PD in Asian populations. Conclusion: Our findings suggest that the SLC6A3 10R may be a protective factor in susceptibility to PD.

Defective Lysosomal Lipid Catabolism as a Common Pathogenic Mechanism for Dementia

Dementia poses an ever-growing burden to health care and social services as life expectancies have grown across the world and populations age. The most common forms of dementia are Alzheimer's disease (AD), vascular dementia, frontotemporal dementia (FTD), and Lewy body dementia, which includes Parkinson's disease (PD) dementia and dementia with Lewy bodies (DLB). Genomic studies over the past 3 decades have identified variants in genes regulating lipid transporters and endosomal processes as major risk determinants for AD, with the most significant being inheritance of the ε4 allele of the APOE gene, encoding apolipoprotein E. A recent surge in research on lipid handling and metabolism in glia and neurons has established defective lipid clearance from endolysosomes as a central driver of AD pathogenesis. The most prevalent genetic risk factors for DLB are the APOE ε4 allele, and heterozygous loss of function mutations in the GBA gene, encoding the lysosomal catabolic enzyme glucocerebrosidase; whilst heterozygous mutations in the GRN gene, required for lysosomal catabolism of sphingolipids, are responsible for a significant proportion of FTD cases. Homozygous mutations in the GBA or GRN genes produce the lysosomal storage diseases Gaucher disease and neuronal ceroid lipofuscinosis. Research from mouse and cell culture models, and neuropathological evidence from lysosomal storage diseases, has established that impaired cholesterol or sphingolipid catabolism is sufficient to produce the pathological hallmarks of dementia, indicating that defective lipid catabolism is a common mechanism in the etiology of dementia.

Clusterin as a Potential Biomarker of Obesity-Related Alzheimer's Disease Risk

Over 35% of the adult US population is obese. In turn, excess adiposity increases the risk of multiple complications including type 2 diabetes (T2D), insulin resistance, and cardiovascular disease; yet, obesity also independently heightens risk of Alzheimer's Disease (AD), even after adjusting for other important confounding risk factors including blood pressure, sociodemographics, cholesterol levels, smoking status, and Apolipoprotein E (ApoE) genotype. Among patients over the age of 65 with dementia, 37% have coexisting diabetes, and an estimated 7.3% of cases of AD are directly attributable to midlife obesity. Clusterin, also known as apolipoprotein J (ApoJ), is a multifunctional glycoprotein that acts as a molecular chaperone, assisting folding of secreted proteins. Clusterin has been implicated in several physiological and pathological states, including AD, metabolic disease, and cardiovascular disease. Despite long-standing interest in elucidating clusterin's relationship with amyloid beta (Aβ) aggregation/clearance and toxicity, significant knowledge gaps still exist. Altered clusterin expression and protein levels have been linked with cognitive and memory function, disrupted central nervous system lipid flux, as well as pathogenic brain structure; and its role in cardiometabolic disease suggests that it may be a link between insulin resistance, dyslipidemia, and AD. Here, we briefly highlight clusterin's relevance to AD by presenting existing evidence linking clusterin to AD and cardiometabolic disease, and discussing its potential utility as a biomarker for AD in the presence of obesity-related metabolic disease.

Associations between CLU polymorphisms and memory performance: The role of serum lipids in Alzheimer's disease

CLU encoding clusterin, has been reported to associate with Alzherimer's disease (AD) by genome-wide association studies (GWAS) based on Caucasian populations. Our previous case-control study has independently confirmed the disease association of CLU in Chinese population. Since little is known about the underlying mechanism of CLU in AD, we have conducted this study to investigate whether the genetic impact of CLU polymorphisms on cognitive functioning is via serum lipid's dysfunction. Three GWAS previously published CLU polymorphisms including rs2279590, rs11136000 and rs9331888, were genotyped in 689 subjects. Serum levels of triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) were measured and tested as mediators. Delayed Word Recall Test (DWRT) was used to evaluate subjects' memory performance. Multiple mediation analysis, a nonparametric procedure to create confidence interval, was performed according to Preacher and Hayes's Bootstrapping method. Our findings suggested significant correlation between CLU polymorphism and DWRT scores for rs11136000 (p = 0.045) after adjustment for age, gender, body mass index, and APOEε4 status, with borderline significant correlation for rs2279590 (p = 0.058). Both T allele of rs11136000 and A allele of rs2279590 were negatively correlated with serum TG levels (p = 0.003; p = 0.001, separately). Moreover, A allele of rs2279590 was positively correlated with serum HDL-C levels (p = 0.015). Consistent with our hypotheses, the genetic impact of CLU polymorphisms on memory performance were partially mediated through TG (rs11136000 95% CI [-0.099,-0.003] and rs2279590 95% CI [-0.104, -0.004]), but not through HDL-C and LDL-C. Our findings indicate CLU polymorphisms may modify AD susceptibility through lipid metabolic pathway.

Association of Polygenic Risk Score with Age at Onset and Cerebrospinal Fluid Biomarkers of Alzheimer's Disease in a Chinese Cohort

To evaluate whether the polygenic profile modifies the development of sporadic Alzheimer's disease (sAD) and pathological biomarkers in cerebrospinal fluid (CSF), 462 sAD patients and 463 age-matched cognitively normal (CN) controls were genotyped for 35 single-nucleotide polymorphisms (SNPs) that are significantly associated with sAD. Then, the alleles found to be associated with sAD were used to build polygenic risk score (PRS) models to represent the genetic risk. Receiver operating characteristic (ROC) analyses and the Cox proportional hazards model were used to evaluate the predictive value of PRS for the sAD risk and age at onset. We measured the CSF levels of Aβ42, Aβ42/Aβ40, total tau (T-tau), and phosphorylated tau (P-tau) in a subgroup (60 sAD and 200 CN participants), and analyzed their relationships with the PRSs. We found that 14 SNPs, including SNPs in the APOE, BIN1, CD33, EPHA1, SORL1, and TOMM40 genes, were associated with sAD risk in our cohort. The PRS models built with these SNPs showed potential for discriminating sAD patients from CN controls, and were able to predict the incidence rate of sAD and age at onset. Furthermore, the PRSs were correlated with the CSF levels of Aβ42, Aβ42/Aβ40, T-tau, and P-tau. Our study suggests that PRS models hold promise for assessing the genetic risk and development of AD. As genetic risk profiles vary among populations, large-scale genome-wide sequencing studies are urgently needed to identify the genetic risk loci of sAD in Chinese populations to build accurate PRS models for clinical practice.

Genetic and Expression Analysis of COPI Genes and Alzheimer's Disease Susceptibility

Alzheimer's disease (AD) is the most common neurodegenerative disease in the elderly and the leading cause of dementia in humans. Evidence shows that cellular trafficking and recycling machineries are associated with AD risk. A recent study found that the coat protein complex I (COPI)-dependent trafficking in vivo could significantly reduce amyloid plaques in the cortex and hippocampus of neurological in the AD mouse models and identified 12 single-nucleotide polymorphisms in COPI genes to be significantly associated with increased AD risk using 6,795 samples. Here, we used a large-scale GWAS dataset to investigate the potential association between the COPI genes and AD susceptibility by both SNP and gene-based tests. The results showed that only rs9898218 was associated with AD risk with P = 0.017. We further conducted an expression quantitative trait loci (eQTLs) analysis and found that rs9898218 G allele was associated with increased COPZ2 expression in cerebellar cortex with P = 0.0184. Importantly, the eQTLs analysis in whole blood further indicated that 11 of these 12 genetic variants could significantly regulate the expression of COPI genes. Hence, these findings may contribute to understand the association between COPI genes and AD susceptibility.

ApoE4: an emerging therapeutic target for Alzheimer's disease

BACKGROUND

The growing body of evidence indicating the heterogeneity of Alzheimer's disease (AD), coupled with disappointing clinical studies directed at a fit-for-all therapy, suggest that the development of a single magic cure suitable for all cases may not be possible. This calls for a shift in paradigm where targeted treatment is developed for specific AD subpopulations that share distinct genetic or pathological properties. Apolipoprotein E4 (apoE4), the most prevalent genetic risk factor of AD, is expressed in more than half of AD patients and is thus an important possible AD therapeutic target.

REVIEW

This review focuses initially on the pathological effects of apoE4 in AD, as well as on the corresponding cellular and animal models and the suggested cellular and molecular mechanisms which mediate them. The second part of the review focuses on recent apoE4-targeted (from the APOE gene to the apoE protein and its interactors) therapeutic approaches that have been developed in animal models and are ready to be translated to human. Further, the issue of whether the pathological effects of apoE4 are due to loss of protective function or due to gain of toxic function is discussed herein. It is possible that both mechanisms coexist, with certain constituents of the apoE4 molecule and/or its downstream signaling mediating a toxic effect, while others are associated with a loss of protective function.

CONCLUSION

ApoE4 is a promising AD therapeutic target that remains understudied. Recent studies are now paving the way for effective apoE4-directed AD treatment approaches.

Gene-environment interactions in Alzheimer's disease: A potential path to precision medicine

Alzheimer's disease (AD) is the leading cause of dementia in the United States and afflicts >5.7 million Americans in 2018. Therapeutic options remain extremely limited to those that are symptom targeting, while no drugs have been approved for the modification or reversal of the disease itself. Risk factors for AD including aging, the female sex, as well as carrying an APOE4 genotype. These risk factors have been extensively examined in the literature, while less attention has been paid to modifiable risk factors, including lifestyle, and environmental risk factors such as exposures to air pollution and pesticides. This review highlights the most recent data on risk factors in AD and identifies gene by environment interactions that have been investigated. It also provides a suggested framework for a personalized therapeutic approach to AD, by combining genetic, environmental and lifestyle risk factors. Understanding modifiable risk factors and their interaction with non-modifiable factors (age, susceptibility alleles, and sex) is paramount for designing personalized therapeutic interventions.

Clusterin in Alzheimer's Disease: Mechanisms, Genetics, and Lessons From Other Pathologies

Clusterin (CLU) or APOJ is a multifunctional glycoprotein that has been implicated in several physiological and pathological states, including Alzheimer's disease (AD). With a prominent extracellular chaperone function, additional roles have been discussed for clusterin, including lipid transport and immune modulation, and it is involved in pathways common to several diseases such as cell death and survival, oxidative stress, and proteotoxic stress. Although clusterin is normally a secreted protein, it has also been found intracellularly under certain stress conditions. Multiple hypotheses have been proposed regarding the origin of intracellular clusterin, including specific biogenic processes leading to alternative transcripts and protein isoforms, but these lines of research are incomplete and contradictory. Current consensus is that intracellular clusterin is most likely to have exited the secretory pathway at some point or to have re-entered the cell after secretion. Clusterin's relationship with amyloid beta (Aβ) has been of great interest to the AD field, including clusterin's apparent role in altering Aβ aggregation and/or clearance. Additionally, clusterin has been more recently identified as a mediator of Aβ toxicity, as evidenced by the neuroprotective effect of CLU knockdown and knockout in rodent and human iPSC-derived neurons. CLU is also the third most significant genetic risk factor for late onset AD and several variants have been identified in CLU. Although the exact contribution of these variants to altered AD risk is unclear, some have been linked to altered CLU expression at both mRNA and protein levels, altered cognitive and memory function, and altered brain structure. The apparent complexity of clusterin's biogenesis, the lack of clarity over the origin of the intracellular clusterin species, and the number of pathophysiological functions attributed to clusterin have all contributed to the challenge of understanding the role of clusterin in AD pathophysiology. Here, we highlight clusterin's relevance to AD by discussing the evidence linking clusterin to AD, as well as drawing parallels on how the role of clusterin in other diseases and pathways may help us understand its biological function(s) in association with AD.

Relationship between Alzheimer's disease-associated SNPs within the CLU gene, local DNA methylation and episodic verbal memory in healthy and schizophrenia subjects

Genetic variation may impact on local DNA methylation patterns. Therefore, information about allele-specific DNA methylation (ASM) within disease-related loci has been proposed to be useful for the interpretation of GWAS results. To explore mechanisms that may underlie associations between Alzheimer's disease (AD) and schizophrenia risk CLU gene and verbal memory, one of the most affected cognitive domains in both conditions, we studied DNA methylation in a region between AD-associated SNPs rs9331888 and rs9331896 in 72 healthy individuals and 73 schizophrenia patients. Using single-molecule real-time bisulfite sequencing we assessed the haplotype-dependent ASM in this region. We then investigated whether its methylation could influence episodic verbal memory measured with the Rey Auditory Verbal Learning Test in these two cohorts. The region showed a complex methylation pattern, which was similar in healthy and schizophrenia individuals and unrelated to haplotypes. The pattern predicted memory scores in controls. The results suggest that epigenetic modifications within the CLU locus may play a role in memory variation, independent of ASM.

Alzheimer's Disease rs11767557 Variant Regulates EPHA1 Gene Expression Specifically in Human Whole Blood

Large-scale genome-wide association studies have reported EPHA1 rs11767557 variant to be associated with Alzheimer's disease (AD) risk in the European population. However, it is still unclear how this variant functionally contributes to the underlying disease pathogenesis. The rs11767557 variant is located approximately 3 kb upstream of EPHA1 gene. We think that rs11767557 may modify the expression of nearby genes such as EPHA1 and further cause AD risk. Until now, the potential association between rs11767557 and the expression of nearby genes has not been reported in previous studies. Here, we evaluate the potential expression association between rs11767557 and EPHA1 using multiple large-scale eQTLs datasets in human brain tissues and the whole blood. The results show that rs11767557 variant could significantly regulate EPHA1 gene expression specifically in human whole blood. These findings may further provide important supplementary information about the regulating mechanisms of rs11767557 variant in AD risk.

Influence of ADAM10 Polymorphisms on Plasma Level of Soluble Receptor for Advanced Glycation End Products and The Association With Alzheimer's Disease Risk

To determine the role of A disintegrin and metalloproteinase 10 (ADAM10) in genetic susceptibility to Alzheimer's disease (AD) in a representative Chinese sample, we genotyped 362 AD patients and 370 healthy controls for the rs514049A/C and rs653765C/T polymorphisms in the ADAM10 promoter using the SNaPshot technique. We also examined the potential impact of these polymorphisms on the plasma level of soluble receptor for advanced glycation end products (sRAGE), a decoy receptor whose reduction has been associated with a higher risk of AD. Additionally, a meta-analysis was performed using the present study and the largest GWAS from the International Genomics of Alzheimer's Project (IGAP). No significant differences were found in the distributions of genotypes or alleles between AD patients and control subjects. However, age-at-onset stratification analysis revealed that there were significant differences in the genotypes (P = 0.015) and alleles (P = 0.006) of the rs653765 SNP. Furthermore, patients with the rs653765 CC genotype showed a lower ADAM10 level and a faster cognitive deterioration than those in patients with the CT/TT genotype in late-onset AD (LOAD), and the rs653765 CC polymorphism was able to regulate the production of the ADAM10 substrate sRAGE. In contrast, the rs514049 polymorphism was not statistically associated with AD. In the meta-analysis, we observed that both rs514049 (A allele vs. C allele, P = 0.002) and rs653765 (C allele vs. T allele, P = 0.004) were associated with AD risk. The present study indicated that the rs653765 polymorphism might be associated with the risk and development of LOAD; in particular, the risk genotype, CC, may decrease the expression of ADAM10, influencing the plasma levels of sRAGE, and thus may be correlated with the clinical progression of AD.

Alzheimer's Disease and Rheumatoid Arthritis: A Mendelian Randomization Study

Alzheimer’s disease (AD) is the most common neurodegenerative disease. In recent years, multiple pathway analyses of AD genome-wide association studies (GWAS) have been conducted, and provided strong support for immune pathways in AD. Rheumatoid arthritis (RA) is a chronic autoimmune disease. It is reported that antirheumatic drugs had protective effect on dementia in RA patients. However, observational studies have reported a controversial inverse relationship between AD and RA. In addition, Mendelian randomization studies have also been performed to evaluate the association of RA with AD. However, these studies reported inconsistent association of RA with AD. Until now, it is still unclear that AD is a causally associated with RA. Here, we performed a Mendelian randomization study to investigate the causal association of AD with RA. We analyzed the large-scale AD GWAS dataset (74,046 individuals) and RA GWAS dataset (58,284 individuals) from the European descent. However, we did not identify any significant association of AD with RA using inverse-variance weighted meta-analysis (IVW), weighted median regression and MR-Egger regression.

Shared Biological Pathways Between Alzheimer's Disease and Ischemic Stroke

Alzheimer's disease (AD) and ischemic stroke (IS) are an immense socioeconomic burden worldwide. There is a possibility that shared genetic factors lead to their links at epidemiological and pathophysiological levels. Although recent genome-wide association studies (GWAS) have provided profound insights into the genetics of AD and IS, no shared genetic variants have been identified to date. This prompted us to initiate this study, which sought to identify shared pathways linking AD and IS. We took advantage of large-scale GWAS summary data of AD (17,008 AD cases and 37,154 controls) and IS (10,307 cases and 19,326 controls) to conduct pathway analyses using genetic pathways from multiple well-studied databases, including GO, KEGG, PANTHER, Reactome, and Wikipathways. Collectively, we discovered that AD and IS shared 179 GO categories (56 biological processes, 95 cellular components, and 28 molecular functions); and the following pathways: six KEGG pathways; two PANTHER pathways; four Reactome pathways; and one in Wikipathways pathway. The more fine-grained GO terms were mainly summarized into different functional categories: transcriptional and post-transcriptional regulation, synapse, endocytic membrane traffic through the endosomal system, signaling transduction, immune process, multi-organism process, protein catabolic metabolism, and cell adhesion. The shared pathways were roughly classified into three categories: immune system; cancer (NSCLC and glioma); and signal transduction pathways involving the cadherin signaling pathway, Wnt signaling pathway, G-protein signaling and downstream signaling mediated by phosphoinositides (PIPs). The majority of these common pathways linked to both AD and IS were supported by convincing evidence from the literature. In conclusion, our findings contribute to a better understanding of common biological mechanisms underlying AD and IS and serve as a guide to direct future research.

Circulating vitamin E levels and Alzheimer's disease: a Mendelian randomization study

Alzheimer's disease (AD) is the leading cause of dementia in older adults. It is more than 50 years since vitamin E was recognized as critical for optimal neurological health. Clinical studies have yielded inconsistent findings on the effect of vitamin E on AD risk. Thus, it remains unclear whether vitamin E levels are genetically associated with AD risk. We performed a Mendelian randomization study to investigate association of circulating vitamin E levels with AD using large-scale vitamin E genome-wide association study data set (N = 7781 individuals of European descent) and AD genome-wide association study data set (N = 54,162 individuals [including 17,008 AD cases and 37,154 controls of European descent]). Mendelian randomization-Egger intercept test showed no significant pleiotropy (β = -0.113; p = 0.296). Inverse-variance weighted (odds ratio = 0.96, 95% confidence interval: 0.47-1.94, p = 0.936) and weighted median analyses (odds ratio = 1.13, 95% confidence interval: 0.35-3.69, p = 0.836) showed no significant association between vitamin E and AD. Together with previous literature, this suggests that vitamin E supplementation may not forestall AD in the general population.

CDH1 rs9929218 variant at 16q22.1 contributes to colorectal cancer susceptibility

Colorectal cancer (CRC) is the third most common cancer. Large-scale genome-wide association studies (GWAS) have been performed and reported some novel CRC susceptibility variants in European ancestry including the CDH1 rs9929218. Following GWAS and candidate studies evaluated the association between the CDH1 rs9929218 polymorphism and CRC in European, Asian and American populations. However, these studies reported inconsistent associations. Evidence shows that rs9929218 may regulate different gene expressions in different human tissues. Here, we reevaluated this association using large-scale samples from 16 studies (n=131768) using a meta-analysis method. In heterogeneity test, we did not identify significant heterogeneity among these studies. Meta-analysis using fixed effect model showed significant association between rs9929218 and CRC (P=6.16E-21, odds ratio (OR) =0.92, 95% confidence interval (CI) 0.91-0.94). In order to validate the effect of rs9929218 variant on CDH1 expression, we further performed a functional analysis using two large-scale expression datasets. We identified significant regulation relation between rs9929218 variant and the expression of CDH1, ZFP90, RP11-354M1.2 and MCOLN2 by both cis-effect and trans-effect. In summary, our analysis highlights significant association between rs9929218 polymorphism and CRC susceptibility.

Association between CLU gene rs11136000 polymorphism and Alzheimer's disease: an updated meta-analysis

Large-scale genome-wide association studies (GWAS) identified that the single nucleotide polymorphism rs11136000 in Clusterin (CLU) gene was associated with risk of Alzheimer's disease (AD) in Caucasian ancestry. However, recent studies reported either a weak association or no association between rs11136000 polymorphism and AD in Asian populations. Therefore, we performed a meta-analysis to explore whether rs11136000 polymorphism is associated with susceptibility to AD in Asian populations. A total of 17 articles including 26 studies with 19,829 cases and 30,900 controls, which were identified by searching PubMed, MEDLINE, and AlzGene up to Nov 2016, were collected for this meta-analysis. The significant association between rs11136000 and AD in the pooled population was found under all the models. In subgroup analysis, we identified significant association in Asian population under the additive mode (OR = 0.90, 95% CI = 0.85-0.96) but not in the recessive model (OR = 0.80, 95% CI = 0.53-1.21) and the dominant model (OR = 0.94, 95% CI = 0.86-1.03). Our analysis further supports previous findings that the rs11136000 polymorphism C allele is associated with AD susceptibility. To our knowledge, this is the new largest meta-analysis to access to the association of CLU rs11136000 polymorphism with AD risk.

EXOC3L2 rs597668 variant contributes to Alzheimer's disease susceptibility in Asian population

Recent genome-wide association studies have established the association between EXOC3L2 rs597668 variant and Alzheimer's disease (AD) in European population. However, recent studies reported inconsistent results in Asian population. Here, we performed a systematic review and meta-analysis to evaluate the impact of rs597668 on AD risk in Asian population using a total of 8686 samples including 2855 cases and 5831 controls. Meanwhile, we selected 17,008 AD cases and 37,154 controls in European population to evaluate the potential heterogeneity between East Asian and European populations. In East Asian population, we identified no potential heterogeneity with P=0.31 and I² = 15.8%. By meta-analysis, we identified positive association between rs597668 and AD risk with P=0.023, OR=0.93, 95% CI 0.87-0.99. We further found significant heterogeneity in pooled Asian and European populations with P<0.0001 and I² = 87.7%. The meta-analysis indicated negative association with P=0.66, OR=0.97, 95% CI 0.85-1.11. In summary, all these findings indicate that rs597668 C allele is a risk factor for AD in European population with OR=1.18 and P=2.49E-13. However the rs597668 C allele played a protective role in AD with OR=0.93 and P=0.023 in East Asian population.

Common genetic variant rs3802842 in 11q23 contributes to colorectal cancer risk in Chinese population

A genome-wide association study identified a common genetic variant rs3802842 at 11q23 to be associated with CRC risk with OR=1.1 and P = 5.80E-10 in European population. In Chinese population, several genetic association studies have investigated the association between rs3802842 variant and CRC risk. However these studies reported both positive and negative association results. It is still necessary to evaluate a specific variant in a specific population, which would be informative to reveal the disease mechanism. Until recently, there is no a systemic study to evaluate the potential association between rs3802842 and CRC risk in Chinese population by a meta-analysis method. Here, we aim to evaluate this association in Chinese population by a meta-analysis method using 12077 samples including 5816 CRC cases and 6261 controls. We identified the T allele of rs3802842 to be significantly related with an increase CRC risk (P=2.22E-05, OR=1.14, 95% CI 1.07-1.21) in Chinese population.

Correlation of rs9331888 polymorphism with Alzheimer's disease among Caucasian and Chinese populations: a meta-analysis and systematic review

Clusterin polymorphism (rs9331888) was reported to be associated with the susceptibility to alzheimer's disease (AD). Nevertheless, the results were inconclusive. To derive a more precise estimation of this association, this meta-analysis was conducted. We've conducted a comprehensive search of PubMed, Embase, CNKI and AlzGene database for case-control studies published throughout October, 2016 that evaluated the role of rs9331888 gene variants in AD patients. Odds ratios (ORs) and their 95% confidence intervals (CIs) were calculated to assess the strength of associations between the rs9331888/C > G polymorphism and AD disease. A total of 9 studies were enrolled in the Meta Analysis. The overall analysis revealed a significant association between the rs9331888/C > G polymorphism and AD disease in the recessive model (GG vs. GC + CC: OR = 1.11, 95% CI: 1.05-1.18; P < 0.01). Sub-group analysis revealed that the Caucasian populations which with recessive model (GG vs. GC + CC: OR = 1.12, 95% CI: 1.06-1.2; P < 0.01) were dramatically related to AD, while no significant association was found in the Chinese populations among the five genetic models. Our meta-analysis demonstrated that the rs9331888/C > G polymorphism in the clusterin gene might contribute to AD susceptibility especially in Caucasian populations. Whereas the relationship of the polymorphism to the disease in Chinese populations was still in controversial. Additional well-designed studies, with larger sample sizes, are required to further elucidate this association.

SMAD7 rs4939827 variant contributes to colorectal cancer risk in Chinese population

A genome-wide association study identified a common genetic variant rs4939827 at 18q21 in SMAD7 to be related with colorectal cancer (CRC) risk with OR=1.2 and P =7.80E-28. Until recently, several meta-analysis studies have been conducted, and reported significant association between rs4939827 and CRC risk. However none of these studies evaluated the potential association between rs4939827 and CRC risk in Chinese population. In this study, we evaluated this association by a meta-analysis using 12077 samples including 5816 CRC cases and 6261 controls. In the end, we identified the T allele of rs4939827 to be significantly related with an increase CRC risk (P=2.22E-05, OR=1.14, 95% CI 1.07-1.21) in Chinese population.

Altered levels of blood proteins in Alzheimer's disease longitudinal study: Results from Australian Imaging Biomarkers Lifestyle Study of Ageing cohort

INTRODUCTION

A blood-based biomarker panel to identify individuals with preclinical Alzheimer's disease (AD) would be an inexpensive and accessible first step for routine testing.

METHODS

We analyzed 14 biomarkers that have previously been linked to AD in the Australian Imaging Biomarkers lifestyle longitudinal study of aging cohort.

RESULTS

Levels of apolipoprotein J (apoJ) were higher in AD individuals compared with healthy controls at baseline and 18 months (P = .0003) and chemokine-309 (I-309) were increased in AD patients compared to mild cognitive impaired individuals over 36 months (P = .0008).

DISCUSSION

These data suggest that apoJ may have potential in the context of use (COU) of AD diagnostics, I-309 may be specifically useful in the COU of identifying individuals at greatest risk for progressing toward AD. This work takes an initial step toward identifying blood biomarkers with potential use in the diagnosis and prognosis of AD and should be validated across other prospective cohorts.

GAB2 rs2373115 variant contributes to Alzheimer's disease risk specifically in European population

A genome-wide association study identified GAB2 rs2373115 to be associated with Alzheimer's disease (AD) risk in European population. However, inconsistent results are reported in East Asian population. Here, we performed an updated analysis using 65,704 samples including 20,982 AD cases and 44,722 controls. First, we investigated the GAB2 rs2373115 variant in Asian population using 3974 AD cases and 7568 controls. To further evaluate the effect of rs2373115 in different populations, we selected 17,008 AD cases and 37,154 controls in European population. We used three genetic models, and found no significant heterogeneity in Asian population. A fixed effect model analysis showed no significant association between rs2373115 and AD in Asian population. There was no significant heterogeneity in the pooled East Asian and European populations. The fixed effect model analysis again showed no significant association between rs2373115 and AD in these pooled populations. Taken together, these findings suggest that GAB2 rs2373115 may contribute to AD susceptibility only in European population but not in East Asian population.

Integrated late onset Alzheimer's disease (LOAD) susceptibility genes: Cholesterol metabolism and trafficking perspectives

Late onset Alzheimer's disease (LOAD) is the most common type of dementia and is characterized by decreased amyloid-β (Aβ) clearance from the brain. Cholesterol regulates the production and clearance of Aβ. Genome-wide association study (GWAS) suggests that at least 20 genes are associated with LOAD. The genes APOE, CLU, SORL1, PICALM, and BIN1 have a relatively high LOAD susceptibility. Additional experimental and bioinformatic approaches to integrate data from genetics, epigenetics, and molecular networks may further increase our understanding of LOAD in relation to cholesterol metabolism and trafficking.

Neither self-reported ethnicity nor declared family origin are reliable indicators of genomic ancestry

Ancestry information can be useful in investigations of diseases with a genetic or infectious background. As the Brazilian population is highly admixed physical traits tend to be poor indicators of ancestry. The assessment of ancestry by ancestry informative markers (AIMs) can exclude the subjectivity of self-declared ethnicity and reported family origin. We aimed to evaluate the reliability of self-reported ethnicity or reported family origin as indicators of genomic ancestry in a female population from the Southeast of Brazil. Two cohorts were included: 404 women asked to self-report their ethnicity (Pop1) and 234 women asked to report their family's origin (Pop2). Identification of AIMs was performed using a panel of 61 markers and results were plotted against parental populations-Amerindian, Western European and Sub-Saharan African-using Structure v2.3.4. In Pop1 57.4 % of women self-reported as white, 34.6 % as brown and 8.0 % as black. Median global European, Amerindian and African contributions were 66.8, 12.6 and 16.6 %. In Pop2, 66.4 % of women declared European origin, 23.9 % African origin and 26.9 % Amerindian. Median global European, Amerindian and African contributions were 80.8, 7.3 and 7.6 %, respectively. Only 31.0 and 21.0 % of the global variation in African and European contributions, respectively, could be explained by self-reported ethnicity and reported family origin only accounted for 20.0 and 5.0 % of the variations observed in African and European ancestries, respectively. Amerindian ancestry did not influence self-reported ethnicity or declared family origin. Neither self-reported ethnicity nor declared family origin are reliable indicators of genomic ancestry in these Brazilian populations.

CR1 rs3818361 Polymorphism Contributes to Alzheimer's Disease Susceptibility in Chinese Population

Recent genome-wide association studies (GWAS) reported CR1 rs3818361 polymorphism to be an Alzheimer's disease (AD) susceptibility variant in European ancestry. Three independent studies investigated this association in Chinese population. However, these studies reported weak or no significant association. Here, we reinvestigated the association using all the samples from three independent studies in Chinese population (N = 4047, 1244 AD cases and 2803 controls). We also selected three independent studies in European ancestry population (N = 11787, 3939 AD cases and 7848 controls) to evaluate the effect of rs3818361 polymorphism on AD risk in different ethnic backgrounds. In Chinese population, we did not identified significant heterogeneity using additive, recessive, and dominant genetic models. Meta-analysis showed significant association between rs3818361 and AD with P = 6.00E-03 and P = 5.00E-03. We further identified no heterogeneity of rs3818361 polymorphism between Chinese and European populations. We found that rs3818361 polymorphism contributed to AD with similar genetic risk in Chinese and European populations. In summary, this is the first study to show significant association between rs3818361 polymorphism and AD in Chinese population by a meta-analysis method. Our findings indicate that the effect of CR1 rs3818361 polymorphism on AD risk in Chinese cohorts is consistent with the increased risk observed in European AD cohorts.