Genetic association of PICALM polymorphisms with Alzheimer's disease in Han Chinese

The relationship of early- and late-onset Alzheimer’s disease genes with COVID-19

Individuals with Alzheimer’s disease and other neurodegenerative diseases have been exposed to excess risk by the COVID-19 pandemic. COVID-19’s main manifestations include high body temperature, dry cough, and exhaustion. Nevertheless, some affected individuals may have an atypical presentation at diagnosis but suffer neurological signs and symptoms as the first disease manifestation. These findings collectively show the neurotropic nature of SARS-CoV-2 virus and its ability to involve the central nervous system. In addition, Alzheimer’s disease and COVID-19 has a number of common risk factors and comorbid conditions including age, sex, hypertension, diabetes, and the expression of APOE ε4. Until now, a plethora of studies have examined the COVID-19 disease but only a few studies has yet examined the relationship of COVID-19 and Alzheimer’s disease as risk factors of each other. This review emphasizes the recently published evidence on the role of the genes of early- or late-onset Alzheimer’s disease in the susceptibility of individuals currently suffering or recovered from COVID-19 to Alzheimer’s disease or in the susceptibility of individuals at risk of or with Alzheimer’s disease to COVID-19 or increased COVID-19 severity and mortality. Furthermore, the present review also draws attention to other uninvestigated early- and late-onset Alzheimer’s disease genes to elucidate the relationship between this multifactorial disease and COVID-19.

Untangling huge literature to disinter genetic underpinnings of Alzheimer's Disease: A systematic review and meta-analysis

Drug discovery for Alzheimer's Disease (AD) is channeled towards unravelling key disease specific drug targets/genes to predict promising therapeutic candidates. Though enormous literature on AD genetics is available, there exists dearth in data pertinent to drug targets and crucial pathological pathways intertwined in disease progression. Further, the research findings revealing genetic associations failed to demonstrate consistency across different studies. This scenario prompted us to initiate a systematic review and meta-analysis with an aim of unearthing significant genetic hallmarks of AD. Initially, a Boolean search strategy was developed to retrieve case-control studies from PubMed, Cochrane, ProQuest, Europe PMC, grey literature and HuGE navigator. Subsequently, certain inclusion and exclusion criteria were framed to shortlist the relevant studies. These studies were later critically appraised using New Castle Ottawa Scale and Q-Genie followed by data extraction. Later, meta-analysis was performed only for those Single Nucleotide Polymorphisms (SNPs) which were evaluated in at least two different ethnicities from two different reports. Among, 204,351 studies retrieved, 820 met our eligibility criteria and 117 were processed for systematic review after critical appraisal. Ultimately, meta-analysis was performed for 23 SNPs associated with 15 genes which revealed significant associations of rs3865444 (CD33), rs7561528 (BIN1) and rs1801133 (MTHFR) with AD risk.

Imaging Genetics Study Based on a Temporal Group Sparse Regression and Additive Model for Biomarker Detection of Alzheimer's Disease

Imaging genetics is an effective tool used to detect potential biomarkers of Alzheimer's disease (AD) in imaging and genetic data. Most existing imaging genetics methods analyze the association between brain imaging quantitative traits (QTs) and genetic data [e.g., single nucleotide polymorphism (SNP)] by using a linear model, ignoring correlations between a set of QTs and SNP groups, and disregarding the varied associations between longitudinal imaging QTs and SNPs. To solve these problems, we propose a novel temporal group sparsity regression and additive model (T-GSRAM) to identify associations between longitudinal imaging QTs and SNPs for detection of potential AD biomarkers. We first construct a nonparametric regression model to analyze the nonlinear association between QTs and SNPs, which can accurately model the complex influence of SNPs on QTs. We then use longitudinal QTs to identify the trajectory of imaging genetic patterns over time. Moreover, the SNP information of group and individual levels are incorporated into the proposed method to boost the power of biomarker detection. Finally, we propose an efficient algorithm to solve the whole T-GSRAM model. We evaluated our method using simulation data and real data obtained from AD neuroimaging initiative. Experimental results show that our proposed method outperforms several state-of-the-art methods in terms of the receiver operating characteristic curves and area under the curve. Moreover, the detection of AD-related genes and QTs has been confirmed in previous studies, thereby further verifying the effectiveness of our approach and helping understand the genetic basis over time during disease progression.

Association of PICALM Gene Polymorphisms with Alzheimer's Disease: Evidence from an Updated Meta-Analysis

BACKGROUND

Previous studies have examined the roles of three polymorphisms (rs3851179, rs541458, and rs592297) of the PICALM gene in susceptibility to Alzheimer's disease (AD) with inconclusive findings.

OBJECTIVE

We performed a meta-analysis to explore whether these three polymorphisms in the PICALM gene were associated with susceptibility to AD.

METHODS

Bibliographical searches were conducted in the PubMed, Embase, Web of Science, and China National Knowledge Infrastructure (CNKI) databases. Summary Odds Ratios (ORs) with 95% Confidence Intervals (CIs) were used to assess the strength of association in a random effects model. Potential sources of heterogeneity were identified by subgroup and meta-regression analyses.

RESULTS

Twenty studies (9,017 cases and 15,448 controls) on rs3851179, 12 studies (8,077 cases and 12,022 controls) on rs541458, and 4 studies (2,106 cases and 2,234 controls) on rs592297 were considered eligible for meta-analyses. For both rs3851179 and rs541458, the overall ORs were significant under all genetic models with mild heterogeneity. Compared with G carriers, A carriers of rs3851179 were associated with a decreased risk of AD (OR = 0.88; 95% CI 0.84, 0.91, P for Z-test <0.001, I2 = 0.0%). Compared with T carriers, C carriers of rs541458 were inversely associated with AD risk (OR = 0.86; 95% CI 0.81, 0.92, P for Z-test <0.001, I2 = 39.5%). No association was observed for rs592297. Subgroup and meta-regression analyses indicated that the protective effect of the rs541458 C allele was observed only among Caucasians, not among Asians (P for interaction: 0.021~<0.001).

CONCLUSION

rs3851179 and rs541458 appear to be associated with decreased AD risk. The null associations for rs592297 with AD risk need further confirmation with a larger number of participants.

Correlation of PICALM polymorphism rs3851179 with Alzheimer's disease among Caucasian and Chinese populations: a meta-analysis and systematic review

The rs3851179 which located at upstream of PICALM was reported to be associated with Alzheimer's disease (AD); however, the relationship is still undefined. To gain a more precise understanding of the association, we conducted a meta-analysis: a comprehensive survey of 16 case-control studies that evaluated the role of rs3851179 gene variants in AD patients. The overall analysis revealed a significant association between the polymorphism and AD in the allelic, homozygote, heterozygote, dominant, and recessive models (p < 0.05). When stratified by ethnicity, a significant association was observed between AD development in Caucasian populations and the five-genetic models; Asian populations, however, featured a significant association in only the allelic, homozygote, and recessive models. We did not observe any influence of APOE ε4 carrier status on the incidence of AD and rs3851179 (p > 0.05). Our meta-analysis thus suggested that the PICALM rs3851179 polymorphism was associated with AD; the APOE ε4 status did not influence the relationship. Nevertheless, considering the limitations of our meta-analysis, further large-scale studies should be conducted to gain a more comprehensive understanding.

Association of lectin-like oxidized low density lipoprotein receptor 1 (OLR1) polymorphisms with late-onset Alzheimer disease in Han Chinese

Background

Lectin-like oxidized low density lipoprotein receptor 1 (OLR1) locates within the area of chromosome 12p, which has been identified as the AD-susceptible region, and plays a role in lipid metabolism. Therefore, it has been suggested to be a good candidate gene for Alzheimer's disease (AD). Several SNPs within OLR1 have been reported to have association with AD among Caucasians.

Methods

We selected and genotyped three SNPs (rs1050283, rs1050286, rs17808009) in OLR1 to investigate its possible relationship with the onset of late-onset Alzheimer disease(LOAD) in 984 LOAD cases and 1,354 healthy controls among northern Han Chinese.

Results

No significant association was found between the OLR1 (rs1050283, rs1050286, rs17808009) polymorphisms and LOAD, even after adjustment for gender and age and stratification for apolipoprotein E (APOE) status.

Conclusions

Our study showed that the SNPs (rs1050283, rs1050286, rs17808009) located in the 3'UTR of OLR1 may not involve in the mechanism of LOAD in Han Chinese population.

State of Play in Alzheimer's Disease Genetics

Alzheimer's disease (AD), the main form of dementia in the elderly, is the most common progressive neurodegenerative disease characterized by rapidly progressive cognitive dysfunction and behavior impairment. AD exhibits a considerable heritability and great advances have been made in approaches to searching the genetic etiology of AD. In AD genetic studies, methods have developed from classic linkage-based and candidate-gene-based association studies to genome-wide association studies (GWAS) and next generation sequencing (NGS). The identification of new susceptibility genes has provided deeper insights to understand the mechanisms underlying AD. In addition to searching novel genes associated with AD in large samples, the NGS technologies can also be used to shed light on the 'black matter' discovery even in smaller samples. The shift in AD genetics between traditional studies and individual sequencing will allow biomaterials of each patient as the central unit of genetic studies. This review will cover genetic findings in AD and consequences of AD genetic findings. Firstly, we will discuss the discovery of mutations in APP, PSEN1, PSEN2, APOE, and ADAM10. Then we will summarize and evaluate the information obtained from GWAS of AD. Finally, we will outline the efforts to identify rare variants associated with AD using NGS.

INPP5D rs35349669 polymorphism with late-onset Alzheimer's disease: A replication study and meta-analysis

Inositol polyphosphate-5-phosphatase (INPP5D) was reported to be associated with Alzheimer's disease (AD) through modulating the inflammatory process and immune response. A recent genome-wide association study discovered a new locus single nucleotide polymorphism (SNP, rs35349669) of INPP5D which was significantly associated with susceptibility to late-onset Alzheimer's disease (LOAD) in Caucasians. In this study, we investigated the relations between the INPP5D polymorphism rs35349669 and LOAD in Han Chinese population comprising 984 LOAD cases and 1352 healthy controls being matched for age and gender. Our results showed no obvious differences in the genotypic or allelic distributions of rs35349669 polymorphism between LOAD cases and healthy controls (genotype: p = 0.167; allele: p = 0.094). Additionally, when these data were stratified by APOEε4 status, there are still no evident differences in the genotypic or allelic distributions in APOEε4 carriers (p > 0.05). Furthermore, meta-analysis of 81964 individuals confirmed that rs35349669 was significantly associated with the risk for LOAD (OR=1.08, 95%CI=1.06-1.11), but the results remained negative in Chinese subgroup (OR=0.77, 95%CI=0.53-1.13). Overall, the current evidence did not indicate that INPP5D rs35349669 polymorphism play a role in the genetic predisposition to LOAD in Chinese population.

MEF2C rs190982 polymorphism with late-onset Alzheimer's disease in Han Chinese: A replication study and meta-analyses

The myocyte enhancer factor (MEF2) family of transcription factors plays a vital role in memory and learning due to its functions in regulating synapse number and reducing dendritic spines. Myocyte enhancer factor 2 C (MEF2C) is regarded as modulator of amyloid-protein precursor (APP) proteolytic processing, in which amyloid-β (Aβ) is produced. A common single nucleotide polymorphism (SNP, rs190982) in MEF2C gene was identified to be related to late-onset Alzheimer's disease (LOAD) in Caucasians in a large meta-analysis of genome-wide association studies (GWAS). Here, we recruited unrelated 984 LOAD patients and 1348 healthy controls matched for gender and age to ascertain whether the rs190982 polymorphism is related to LOAD in Han Chinese. No difference in the genotype and allele distributions of the MEF2C rs190982 polymorphism was found between LOAD cases and healthy controls (genotype: P = 0.861; allele: P = 0.862), even after stratification for APOE ε4 allele as well as statistical adjustment for age, gender and APOE ε4 status. Furthermore, the meta-analysis in 4089 Chinese individuals did not detect the association of rs190982 within MEF2C with the risk for LOAD (OR = 1.03, 95%CI = 0.90-1.18). Overall, the current evidence did not support the relation between rs190982 polymorphism within MEF2C and the LOAD risk in Northern Han Chinese.

NME8 rs2718058 polymorphism with Alzheimer's disease risk: a replication and meta-analysis

Recently, a large meta-analysis of five genome wide association studies (GWAS) has identified that a novel single nucleotide polymorphism (SNP) rs2718058, adjacent to gene NME8 on chromosome 7p14.1, was associated with late-onset Alzheimer's disease (LOAD) in Caucasians. However, the effect of rs2718058 on other populations remains unclear. In order to explore the relationship between rs2718058 and LOAD risk in a North Han Chinese population, we recruited 984 LOAD cases and 1354 healthy controls that matched for sex and age in this study. The results showed no significant differences in the genotypic or allelic distributions of rs2718058 polymorphism between LOAD cases and healthy controls, even though after stratification for APOE ε4 status and statistical adjustment for age, gender and APOE ε4 status (p > 0.05). However, a meta-analysis conducted in a sample of 82513 individuals confirmed a significant association between SNP rs2718058 and LOAD risk (OR = 1.08, 95%CI = 1.05-1.11) in the whole population. But there was still no positive results in Chinese subgroup (OR = 1.05, 95%CI = 0.93-1.17). In conclusion, the rs2718058 near gene NME8 on chromosome 7p14.1 might not play a major role in the genetic predisposition to LOAD in the North Han Chinese.

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.

Association of HLA-DRB1 polymorphism with Alzheimer's disease: a replication and meta-analysis

Genome-wide association studies (GWAS) have identified one single-nucleotide polymorphism (SNP) rs9271192 within HLA-DRB1 as a risk factor for Alzheimer's disease (AD) in Caucasians. The effect of rs9271192 on AD needed to be verified in other ethnic cohorts. In order to evaluate the association between HLA-DRB1 rs9271192 polymorphism and late-onset AD (LOAD) in the Northern Han Chinese population, we recruited 982 LOAD patients and 1344 sex- and age-matched healthy controls. The results showed that HLA-DRB1 rs9271192 was associated with LOAD (genotype P = 0.015, allele P = 0.04). The results of logistic regression revealed the C allele homozygosity strongly increased the risk of LOAD under a recessive model in the total sample (P = 0.004, OR =2.069, 95% CI = 1.262–3.434). When these data were stratified by apolipoprotein E (APOE) ε4 status, the observed association was confined to APOE ε4 non-carriers (additive model: P=0.048, OR =1.191, 95% CI =1.001–1.417; recessive model: P < 0.001, OR = 2.601, 95% CI =1.519–4.566). Furthermore, meta-analysis after sensitive analysis confirmed that rs9271192 within HLA-DRB1 increased the risk of LOAD (OR = 1.12, 95% CI = 1.08–1.15). To summarize, the C allele in HLA-DRB1 rs9271192 may be an independent risk factor for LOAD.

rs3851179 Polymorphism at 5' to the PICALM Gene is Associated with Alzheimer and Parkinson Diseases in Brazilian Population

Alzheimer's (AD) and Parkinson's diseases (PD) share clinical and pathological features, suggesting that they could have common pathogenic mechanisms, as well as overlapping genetic modifiers. Here, we performed a case-control study in a Brazilian population to clarify whether the risk of AD and PD might be influenced by shared polymorphisms at PICALM (rs3851179), CR1 (rs6656401) and CLU (rs11136000) genes, which were previously identified as AD risk factors by genome-wide association studies. For this purpose, 174 late-onset AD patients, 166 PD patients and 176 matched controls were genotyped using TaqMan^® assays. The results revealed that there were significant differences in genotype and allele frequencies for the SNP PICALM rs3851179 between AD/PD cases and controls, but none for CR1 rs6656401 and CLU rs11136000 intronic polymorphisms. After stratification by APOE ε4 status, the protective effect of the PICALM rs3851179 A allele in AD cases remains evident only in APOE ε4 (-) carriers, suggesting that the APOE ε4 risky allele weakens its protective effect in the APOE ε4 (+) subgroup. More genetic studies using large-sized and well-defined matched samples of AD and PD patients from mixed populations as well as functional correlation analysis are urgently needed to clarify the role of rs3851179 in the AD/PD risk. An understanding of the contribution of rs3851179 to the development of AD and PD could provide new targets for the development of novel therapies.

The impact of PICALM genetic variations on reserve capacity of posterior cingulate in AD continuum

Phosphatidylinositolbinding clathrin assembly protein (PICALM) gene is one novel genetic player associated with late-onset Alzheimer’s disease (LOAD), based on recent genome wide association studies (GWAS). However, how it affects AD occurrence is still unknown. Brain reserve hypothesis highlights the tolerant capacities of brain as a passive means to fight against neurodegenerations. Here, we took the baseline volume and/or thickness of LOAD-associated brain regions as proxies of brain reserve capacities and investigated whether PICALM genetic variations can influence the baseline reserve capacities and the longitudinal atrophy rate of these specific regions using data from Alzheimer’s Disease Neuroimaging Initiative (ADNI) dataset. In mixed population, we found that brain region significantly affected by PICALM genetic variations was majorly restricted to posterior cingulate. In sub-population analysis, we found that one PICALM variation (C allele of rs642949) was associated with larger baseline thickness of posterior cingulate in health. We found seven variations in health and two variations (rs543293 and rs592297) in individuals with mild cognitive impairment were associated with slower atrophy rate of posterior cingulate. Our study provided preliminary evidences supporting that PICALM variations render protections by facilitating reserve capacities of posterior cingulate in non-demented elderly.

Meta-analysis of the Association between Alzheimer Disease and Variants in GAB2, PICALM, and SORL1

The genetic variants play a crucial role in the pathogenesis of Alzheimer's disease (AD), while the relationships of specific single nucleotide polymorphisms (SNPs) with AD are still controversial. We performed the meta-analysis to obtain a more precise estimation of whether growth factor receptor-bound protein-associated binding protein 2 (GAB2), phosphatidylinositol binding clathrin assembly protein (PICALM), and sortilin-related receptor (SORL1) variants are associated with AD. Databases including PubMed, Embase, and Cochrane Library were searched to find relevant studies. Cochran's Q-statistic and I ² were used to assess the heterogeneity among the included studies. Odds ratios (OR) and 95 % confidence intervals (95 % CIs) were conducted to evaluate the association between the SNP and the susceptibility to AD. Publication bias was estimated by funnel plots. All of the statistical analyses were implemented using R Version 3.2.1 software. A total of 35 case-control studies involving 15 SNPs were included. There was no significant association between SNPs of GAB2 rs2373115 (G > T) and PICALM rs541458 (C > T) and AD. The allele T of rs3851179 in PICALM was associated with a 13 % increase in the risk of AD. Seven SNPs on SORL1 were significantly associated with AD. Four SNPs, including rs1010159*T, rs641120*A, rs668387*T, and rs689021*A, were associated with a decreased risk of AD, while the other three SNPs, including rs12285364*T, rs2070045*G, and rs2282649*T, were all associated with an increased risk of AD. The results of the present study suggested that multiple gene variants were associated with AD. The SNP of rs3851179 (PICALM), rs12285364 (SORL1), rs2070045 (SORL1), and rs2282649 (SORL1) was associated with an increased risk of AD, whereas SORL1 rs1010159, rs641120, rs668387, and rs689021 were associated with a decreased risk of AD.

p53 prevents neurodegeneration by regulating synaptic genes

DNA damage has been implicated in neurodegenerative disorders, including Alzheimer's disease and other tauopathies, but the consequences of genotoxic stress to postmitotic neurons are poorly understood. Here we demonstrate that p53, a key mediator of the DNA damage response, plays a neuroprotective role in a Drosophila model of tauopathy. Further, through a whole-genome ChIP-chip analysis, we identify genes controlled by p53 in postmitotic neurons. We genetically validate a specific pathway, synaptic function, in p53-mediated neuroprotection. We then demonstrate that the control of synaptic genes by p53 is conserved in mammals. Collectively, our results implicate synaptic function as a central target in p53-dependent protection from neurodegeneration.

The Role of PICALM in Alzheimer's Disease

Alzheimer's disease (AD) is a highly heritable disease (with heritability up to 76%) with a complex genetic profile of susceptibility, among which large genome-wide association studies (GWASs) pointed to the phosphatidylinositol-binding clathrin assembly protein (PICALM) gene as a susceptibility locus for late-onset Alzheimer's disease (LOAD) incidence. Here, we summarize the known functions of PICALM and discuss its genetic polymorphisms and their potential physiological effects associated with LOAD. Compelling data indicated that PICALM affects AD risk primarily by modulating production, transportation, and clearance of β-amyloid (Aβ) peptide, but other Aβ-independent pathways are discussed, including tauopathy, synaptic dysfunction, disorganized lipid metabolism, immune disorder, and disrupted iron homeostasis. Finally, given the potential involvement of PICALM in facilitating AD occurrence in multiple ways, it might be possible that targeting PICALM might provide promising and novel avenues for AD therapy.

An intronic PICALM polymorphism, rs588076, is associated with allelic expression of a PICALM isoform

BACKGROUND

Although genome wide studies have associated single nucleotide polymorphisms (SNP)s near PICALM with Alzheimer's disease (AD), the mechanism underlying this association is unclear. PICALM is involved in clathrin-mediated endocytosis and modulates Aß clearance in vitro. Comparing allelic expression provides the means to detect cis-acting regulatory polymorphisms. Thus, we evaluated whether PICALM showed allele expression imbalance (AEI) and whether this imbalance was associated with the AD-associated polymorphism, rs3851179.

RESULTS

We measured PICALM allelic expression in 42 human brain samples by using next-generation sequencing. Overall, PICALM demonstrated equal allelic expression with no detectable influence by rs3851179. A single sample demonstrated robust global PICALM allelic expression imbalance (AEI), i.e., each of the measured isoforms showed AEI. Moreover, the PICALM isoform lacking exons 18 and 19 (D18-19 PICALM) showed significant AEI in a subset of individuals. Sequencing these individuals and subsequent genotyping revealed that rs588076, located in PICALM intron 17, was robustly associated with this imbalance in D18-19 PICALM allelic expression (p = 9.54 x 10-5). This polymorphism has been associated previously with systolic blood pressure response to calcium channel blocking agents. To evaluate whether this polymorphism was associated with AD, we genotyped 3269 individuals and found that rs588076 was modestly associated with AD. However, when both the primary AD SNP rs3851179 was added to the logistic regression model, only rs3851179 was significantly associated with AD.

CONCLUSIONS

PICALM expression shows no evidence of AEI associated with rs3851179. Robust global AEI was detected in one sample, suggesting the existence of a rare SNP that strongly modulates PICALM expression. AEI was detected for the D18-19 PICALM isoform, and rs588076 was associated with this AEI pattern. Conditional on rs3851179, rs588076 was not associated with AD risk, suggesting that D18-19 PICALM is not critical in AD. In summary, this analysis of PICALM allelic expression provides novel insights into the genetics of PICALM expression and AD risk.

Association of IL-12A and IL-12B polymorphisms with Alzheimer's disease susceptibility in a Han Chinese population

As a pro-inflammatory cytokine belonging to the interleukin (IL)-1 family, IL-12 is recently found to be involved in the pathogenesis of Alzheimer's disease (AD). Here, we investigated the relations of three potentially functional single nucleotide polymorphisms (SNPs) in IL-12A (rs2243115 and rs568408) and IL-12B (rs3212227) with late-onset AD (LOAD) risk in a Northern Han Chinese cohort containing 1133 patients and 1158 healthy controls. Our findings indicated that these SNPs in IL-12A and IL-12B can individually and jointly contribute to LOAD risk in Han Chinese, implying that the genes encoding IL-12 subunits represent novel genetic risk factors for LOAD susceptibility.

ABCA7 in Alzheimer's Disease

ATP-binding cassette A7 (ABCA7) gene has recently been identified as a strong genetic locus associated with late-onset Alzheimer's disease (LOAD) through genome-wide association studies (GWASs). ABCA7 is a member of the ATP-binding cassette (ABC) transporter gene superfamily, which codes for 49 ABC proteins, divided into 7 subfamilies (coded A-G). As a multispan transmembrane protein, ABCA7 is most abundantly expressed in the microglial cells in the brain. The levels of ABCA7 have been detected to be increased in the Alzheimer's disease (AD) brain, which positively correlated with amyloid plaque burden and disease severity. Emerging data suggests that ABCA7 could be associated with AD via various pathways, possibly including amyloid-β (Aβ) accumulation, lipid metabolism, and phagocytosis. In this review, we summarize the known functions of ABCA7 and discuss the single-nucleotide polymorphisms (SNPs) related to LOAD, as well as their potential physiological effects. Finally, given the contributions of ABCA7 to AD pathogenesis, targeting ABCA7 might provide novel opportunities for AD therapy.

Early onset Alzheimer's disease and oxidative stress

Alzheimer's disease (AD) is the most common cause of dementia in elderly adults. It is estimated that 10% of the world's population aged more than 60-65 years could currently be affected by AD, and that in the next 20 years, there could be more than 30 million people affected by this pathology. One of the great challenges in this regard is that AD is not just a scientific problem; it is associated with major psychosocial and ethical dilemmas and has a negative impact on national economies. The neurodegenerative process that occurs in AD involves a specific nervous cell dysfunction, which leads to neuronal death. Mutations in APP, PS1, and PS2 genes are causes for early onset AD. Several animal models have demonstrated that alterations in these proteins are able to induce oxidative damage, which in turn favors the development of AD. This paper provides a review of many, although not all, of the mutations present in patients with familial Alzheimer's disease and the association between some of these mutations with both oxidative damage and the development of the pathology.

Genetic variation in PICALM and Alzheimer's disease risk in Han Chinese

The current study was conducted to investigate the association of phosphatidylinositol-binding clathrin assembly protein gene (PICALM) with late-onset Alzheimer's disease (LOAD) risk in Han Chinese. We first sequenced PICALM for variants in a small sample (n = 100), and the selected variants were then genotyped in a larger cohort (n = 2292). Sequencing analysis identified 16 variants within PICALM including 5 new variants with extreme low frequency in the northern Han Chinese population. However, in the subsequent genotyping, none showed a significant association with LOAD risk after Bonferroni correction. These findings implicate that PICALM might not play a major role in the genetic predisposition to LOAD in Han Chinese.

George-Hyslop P, Mayeux R, Haines JL, Pericak-Vance MA, Yoshida M, Nishida N, Tokunaga K, Yamamoto K, Tsuji S, Kanazawa I, Ihara Y, Schellenberg GD, Farrer LA, Kuwano R. SORL1 is genetically associated with late-onset Alzheimer's disease in Japanese, Koreans and Caucasians

To discover susceptibility genes of late-onset Alzheimer's disease (LOAD), we conducted a 3-stage genome-wide association study (GWAS) using three populations: Japanese from the Japanese Genetic Consortium for Alzheimer Disease (JGSCAD), Koreans, and Caucasians from the Alzheimer Disease Genetic Consortium (ADGC). In Stage 1, we evaluated data for 5,877,918 genotyped and imputed SNPs in Japanese cases (n = 1,008) and controls (n = 1,016). Genome-wide significance was observed with 12 SNPs in the APOE region. Seven SNPs from other distinct regions with p-values <2×10(-5) were genotyped in a second Japanese sample (885 cases, 985 controls), and evidence of association was confirmed for one SORL1 SNP (rs3781834, P = 7.33×10(-7) in the combined sample). Subsequent analysis combining results for several SORL1 SNPs in the Japanese, Korean (339 cases, 1,129 controls) and Caucasians (11,840 AD cases, 10,931 controls) revealed genome wide significance with rs11218343 (P = 1.77×10(-9)) and rs3781834 (P = 1.04×10(-8)). SNPs in previously established AD loci in Caucasians showed strong evidence of association in Japanese including rs3851179 near PICALM (P = 1.71×10(-5)) and rs744373 near BIN1 (P = 1.39×10(-4)). The associated allele for each of these SNPs was the same as in Caucasians. These data demonstrate for the first time genome-wide significance of LOAD with SORL1 and confirm the role of other known loci for LOAD in Japanese. Our study highlights the importance of examining associations in multiple ethnic populations.

Association of GWAS-linked loci with late-onset Alzheimer's disease in a northern Han Chinese population

OBJECTIVE

Five genomewide association studies (GWAS) in white populations have recently identified and confirmed 9 novel Alzheimer's disease (AD) susceptibility loci (CLU, CR1, PICALM, BIN1, ABCA7, MS4A gene cluster, CD2AP, CD33, and EPHA1). These studies have been conducted almost exclusively in white populations and it is unclear whether these observations generalize to populations with different ethnicities.

METHODS

We recruited 1224 unrelated northern Han Chinese subjects comprising 612 patients with a clinical diagnosis of late-onset AD (LOAD) according to the criteria of the National Institute of Neurological and Communicative Diseases and Stroke/Alzheimer's Disease and Related Disorders Association and 612 healthy age- and sex-matched control subjects. Because of our previous study investigating CLU, CR1, and PICALM in the Han population, we limited the current analysis to BIN1, ABCA7, MS4A gene cluster, CD2AP, CD33, and EPHA1.

RESULTS

In a multivariate analysis, associations of MS4A6A (rs610932; odds ratio = 0.632, Bonferroni corrected P = .019) and CD33 (rs3865444; odds ratio = 1.492, Bonferroni corrected P = .017) with LOAD were replicated successfully. When these data were stratified by apolipoprotein E (APOE) ε4 status, both rs610932 and rs610932 were evident only among subjects without the APOE ε4 allele. For BIN1, assuming a dominant model of inheritance, a positive association for rs7561528 in APOE ε4 carriers was observed. This association, however, did not remain significant after Bonferroni correction. As for ABCA7, CD2AP, and EPHA1 single nucleotide polymorphisms from recent GWAS, despite the similar directional effects, no significant differences in genotype and estimated allele frequency distribution between patients and control subjects were observed.

CONCLUSIONS

This study provides the first independent evidence that MS4A and CD33 loci are associated with the risk of LOAD in northern Han Chinese population. Genotypes at the two loci confer risk predominantly in APOE ε4-negative subjects.

Identification and confirmation of an exonic splicing enhancer variation in exon 5 of the Alzheimer disease associated PICALM gene

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by memory and cognitive impairment and is the leading cause of dementia in the elderly. A number of genome wide association studies and subsequent replication studies have been published recently on late onset AD (LOAD). These studies identified several new susceptibility genes including phosphatidylinositol-binding clathrin assembly protein (PICALM) on chromosome 11. The aim of our study was to examine the entire coding sequence of PICALM to determine if the association could be explained by any previously undetected sequence variation. Therefore, we sequenced 48 cases and 48 controls homozygous for the risk allele in the signal SNP rs3851179. We did not find any new variants; however, rs592297, a known coding synonymous SNP that is part of an exonic splice enhancer region in exon 5, is in strong linkage disequilibrium with rs3851179 and should be examined for functional significance in Alzheimer pathophysiology.

Lack of association between PICALM rs3851179 polymorphism and Alzheimer's disease in Chinese population and APOEε4-negative subgroup

Recently, the association between PICALM rs3851179 polymorphism and Alzheimer's disease (AD) was investigated in the Chinese population by 3 independent studies. However, both allele and genotype tests failed to reveal any association. The association was identified only in the APOEε4-negative subgroup. We think that the failure to replicate the association may be because of the relatively small sample size. In this research, we reinvestigated the association using all the samples from these 3 studies (n = 2486, and 1202 cases and 1284 control subjects). We failed to replicate this association between the rs3851179 polymorphism and AD in all samples and the APOEε4-negative subgroup. Our results indicate that rs3851179 may not be an AD susceptibility locus in the Chinese population and the APOEε4-negative subgroup.

Association studies of 19 candidate SNPs with sporadic Alzheimer's disease in the North Chinese Han population

Genome-wide association studies (GWAS) identified multiple single-nucleotide polymorphisms (SNPs) that are associated with the pathogenesis of Alzheimer's disease (AD). As replication in independent studies remains the only way to validate proposed GWAS signals, we detect SNPs reported in the GWAS, in order to explore their association with sporadic AD (SAD) in the Chinese population. We analyzed genotype and allele distributions of 19 SNPs reported in GWAS in 191 SAD patients and 180 healthy controls. We found that higher frequencies of rs10868366 G and rs7019241 C carriers were observed in SAD patients compared with controls (rs10868366 G: P = 0.026, odds ratio (OR) = 1.4, 95% confidence intervals (CI) 1.0-1.9; rs7019241 C: P = 0.019, OR 1.4, 95% CI 1.6-1.9). Furthermore, rs10868366 G/T and rs7019241 C/T in GOLPH2 were in strong linkage disequilibrium and formed a relative protective factor rs10868366 T/rs7019241 T and a relative risk factor rs10868366 G/rs7019241 C. For SNP rs3826656 in near gene 5' region of CD33, the results revealed that in subjects with APOE ε4 alleles, the A allele was associated with a reduced risk of SAD compared with the G allele (OR 0.479; 95% CI 0.263-0.870, P = 0.015), and AA genotype was associated with a reduced risk of SAD compared with the genotype AG + GG (OR 0.395; 95% CI 0.158-0.659, P = 0.008). Our results support the view that rs10868366 and rs7019241 in GOLPH2 and rs3826656 in near gene 5' region of CD33 are significantly associated with SAD in the north Chinese Han population.

Replication of EPHA1 and CD33 associations with late-onset Alzheimer's disease: a multi-centre case-control study

BACKGROUND

A recently published genome-wide association study (GWAS) of late-onset Alzheimer's disease (LOAD) revealed genome-wide significant association of variants in or near MS4A4A, CD2AP, EPHA1 and CD33. Meta-analyses of this and a previously published GWAS revealed significant association at ABCA7 and MS4A, independent evidence for association of CD2AP, CD33 and EPHA1 and an opposing yet significant association of a variant near ARID5B. In this study, we genotyped five variants (in or near CD2AP, EPHA1, ARID5B, and CD33) in a large (2,634 LOAD, 4,201 controls), independent dataset comprising six case-control series from the USA and Europe. We performed meta-analyses of the association of these variants with LOAD and tested for association using logistic regression adjusted by age-at-diagnosis, gender, and APOE ε4 dosage.

RESULTS

We found no significant evidence of series heterogeneity. Associations with LOAD were successfully replicated for EPHA1 (rs11767557; OR = 0.87, p = 5 × 10-4) and CD33 (rs3865444; OR = 0.92, p = 0.049), with odds ratios comparable to those previously reported. Although the two ARID5B variants (rs2588969 and rs494288) showed significant association with LOAD in meta-analysis of our dataset (p = 0.046 and 0.008, respectively), the associations did not survive adjustment for covariates (p = 0.30 and 0.11, respectively). We had insufficient evidence in our data to support the association of the CD2AP variant (rs9349407, p = 0.56).

CONCLUSIONS

Our data overwhelmingly support the association of EPHA1 and CD33 variants with LOAD risk: addition of our data to the results previously reported (total n > 42,000) increased the strength of evidence for these variants, providing impressive p-values of 2.1 × 10-15 (EPHA1) and 1.8 × 10-13 (CD33).