Meta-analyses of 8 polymorphisms associated with the risk of the Alzheimer's disease

Alpha 2-Macroglobulin Polymorphisms and Susceptibility to Alzheimer's Disease: A Comprehensive Meta-Analysis Based on 62 Studies

Background

The relationship between alpha 2-macroglobulin (A2M) gene and Alzheimer's disease (AD) has been widely studied across populations; however, the results are inconsistent.

Objective

This study aimed to evaluate the association of A2M gene with AD by the application of meta-analysis.

Methods

Relevant studies were identified by comprehensive searches. The quality of each study was assessed using the Newcastle-Ottawa Scale. Allele and genotype frequencies were extracted from each of the included studies. Odds ratio (OR) with corresponding 95% confidence intervals (CI) was calculated using a random-effects or fixed-effects model. The Cochran Q statistic and I2 metric was used to evaluate heterogeneity, and Egger's test and Funnel plot were used to assess publication bias.

Results

A total of 62 studies were identified and included in the current meta-analysis. The G allele of rs226380 reduced AD risk (OR: 0.64, 95% CI: 0.47-0.87, pFDR = 0.012), but carrier with the TT genotype was more likely to develop AD in Asian populations (OR: 1.56, 95% CI: 1.12-2.19, pFDR = 0.0135). The V allele of the A2M-I/V (rs669) increased susceptibility to AD in female population (OR, 95% CI: 2.15, 1.38-3.35, pFDR = 0.0024); however, the II genotype could be a protective factor in these populations (OR, 95% CI: 0.43, 0.26-0.73, pFDR = 0.003). Sensitivity analyses confirmed the reliability of the original results.

Conclusions

Existing evidence indicate that A2M single nucleotide polymorphisms (SNPs) may be associated with AD risk in sub-populations. Future studies with larger sample sizes will be necessary to confirm the results.

The role of opioid receptors in modulating Alzheimer's Disease

Alzheimer's disease (AD) is a complex neurological disorder characterized by accumulation of amyloid plaques and neurofibrillary tangles. Long term investigation of AD pathogenesis suggests that β-site amyloid precursor protein [APP] cleaving enzyme 1 (BACE1) and γ-secretase enzymes promote the amyloidogenic pathway and produce toxic Aβ peptides that are predisposed to aggregate in the brain. Hence, the targeted inhibition of BACE1/γ-secretase expression and function is a promising approach for AD therapy. Several reports have suggested that the opioid family of G-protein coupled receptors modulate the etiology of AD progression. It has also been found that changes in the signaling pathways of opioid receptors increased the expression of BACE1 and γ-secretase, and is strongly correlated with abnormal production of Aβ and pathogenesis of AD. Thus, the opioid receptor family is a promising candidate for targeted drug development to treat AD. In this review, we outline the involvement and mechanisms of opioid receptor signaling modulation in Alzheimer's Disease progression.

Mutations in SORL1 and MTHFDL1 possibly contribute to the development of Alzheimer's disease in a multigenerational Colombian Family

Alzheimer's disease (AD) is the most common cause of dementia in the elderly, affecting over 50 million people worldwide in 2020 and this number will triple to 152 million by 2050. Much of the increase will be in developing countries like Colombia. In familial forms, highly penetrant mutations have been identified in three genes, APP, PSEN1, and PSEN2, supporting a role for amyloid-β peptide. In sporadic forms, more than 30 risk genes involved in the lipid metabolism, the immune system, and synaptic functioning mechanisms. We used whole-exome sequencing (WES) to evaluate a family of 97 members, spanning three generations, with a familiar AD, and without mutations in APP, PSEN1, or PSEN2. We sequenced two affected and one unaffected member with the aim of identifying genetic variants that could explain the presence of the disease in the family and the candidate variants were validated in eleven members. We also built a structural model to try to determine the effect on protein function. WES analysis identified two rare variants in SORL1 and MTHFD1L genes segregating in the family with other potential risk variants in APOE, ABCA7, and CHAT, suggesting an oligogenic inheritance. Additionally, the structural 3D models of SORL1 and MTHFD1L variants shows that these variants produce polarity changes that favor hydrophobic interactions, resulting in local structural changes that could affect the protein function and may contribute to the development of the disease in this family.

The role of ATP-binding cassette subfamily A in the etiology of Alzheimer's disease

Background

Alzheimer’s disease (AD) is the leading cause of dementia, clinically characterized by memory deficits and progressive cognitive decline. Despite decades of research effective therapies are lacking, and a large part of the genetic heritability remains unidentified. ABCA7 and ABCA1, members of the ATP-binding cassette subfamily A (ABCA), were identified as AD risk genes in genome-wide association studies. Nevertheless, genetic and/or functional studies propose a link between AD and two other members of the ABCA subclass, i.e., ABCA2 and ABCA5.

Main body

Changes in expression or dysfunction of these transporters were found to increase amyloid β levels. This might be related to the common role of ABCA transporters in cellular cholesterol homeostasis, for which a prominent role in AD development has been suggested. In this review, we provide a comprehensive overview and discussion on the contribution of the ABCA subfamily to the etiopathogenesis of AD.

Conclusions

A better understanding of the function and identification of disease-associated genetic variants in ABCA transporters can contribute to the development of novel therapeutic strategies for AD.

Association Between Common Variants of APOE, ABCA7, A2M, BACE1, and Cerebrospinal Fluid Biomarkers in Alzheimer's Disease: Data from the PUMCH Dementia Cohort

Background:

The previous studies have identified several genes in relation to Alzheimer’s disease (AD), such as ABCA7, CR1, etc. A few studies have explored the association between the common variants, mainly in the non-coding regions of these genes, and cerebrospinal fluid (CSF) biomarkers. Fewer studies target the variants in the coding regions.

Objective:

To illustrate the association between the common variants within or adjacent to the coding regions of AD susceptible genes and CSF biomarkers in AD patients.

Methods:

75 sporadic probable AD patients were extracted from the dementia cohort of Peking Union Medical College Hospital. They all had history inquiry, physical examination, blood test, cognitive assessment, brain MRI, CSF testing of Aβ₄₂, ¹⁸¹p-tau, and t-tau, and next-generation DNA sequencing. Sixty-nine common single nucleotide polymorphisms (SNPs) (minor allele frequency > 0.01) within or near the coding region of 13 AD susceptible genes were included in the analysis.

Results:

The rs7412-CC (APOE) genotype showed lower CSF Aβ₄₂ level and higher p-tau/Aβ₄₂ ratio than the rs7412-CT genotype. The rs3752246-C (ABCA7) allele correlated with lower CSF Aβ₄₂ level. The alternate alleles of six ABCA7 SNPs were related to lower CSF p-tau, including rs3745842, rs3764648, rs3764652, rs4147930, rs4147934 and rs881768. The rs11609582-TT (A2M) genotype showed higher CSF p-tau than the rs11609582-TA genotype. The p-tau/Aβ₄₂ ratio was higher in the rs490460-TT (BACE1) genotype relative to the rs490460-GT genotype.

Conclusion:

Some common variants within or near the coding regions of APOE, ABCA7, A2M, and BACE1 are associated with CSF Aβ₄₂, p-tau. or p-tau/Aβ₄₂.

Amyloid Beta Dynamics in Biological Fluids—Therapeutic Impact

Despite the significant impact of Alzheimer’s disease (AD) at individual and socioeconomic levels and the numerous research studies carried out on this topic over the last decades, the treatments available in daily clinical practice remain less than satisfactory. Among the accepted etiopathogenic hypotheses, the amyloidogenic pathway theory, although intensively studied and even sometimes controversial, is still providing relevant theoretical elements for understanding the etiology of AD and for the further development of possible therapeutic tools. In this sense, this review aims to offer new insights related to beta amyloid (Aβ), an essential biomarker in AD. First the structure and function of Aβ in normal and pathological conditions are presented in detail, followed by a discussion on the dynamics of Aβ at the level of different biological compartments. There is focus on Aβ elimination modalities at central nervous system (CNS) level, and clearance via the blood–brain barrier seems to play a crucial/dominant role. Finally, different theoretical and already-applied therapeutic approaches for CNS Aβ elimination are presented, including the recent “peripheral sink therapeutic strategy” and “cerebrospinal fluid sinks therapeutic strategy”. These data outline the need for a multidisciplinary approach designed to deliver a solution to stimulate Aβ clearance in more direct ways, including from the cerebrospinal fluid level.

Association between the lipoprotein lipase rs1534649 gene polymorphism in intron one with Body Mass Index and High Density Lipoprotein-Cholesterol

Lipoprotein lipase (LPL) is an enzyme involved in lipid metabolism and distribution of fatty acids hence its role in the initiation and development of dyslipidemia and adiposity. Single nucleotide polymorphisms (SNPs) across the LPL gene have been associated with dyslipidemia, however, the association with obesity has been limited towards specific populations. This study examined the association between LPL gene polymorphisms with plasma lipid levels and body mass index (BMI) in the Kuwaiti population. We examined a total of 486 adults (303 and 183 females and males respectively) with plasma lipid levels and BMI. DNA samples were genotyped for two LPL gene polymorphisms (rs1534649 and rs28645722) using TaqMan allelic discrimination. The relationship between the genotypes with both plasma lipid levels and BMI were assessed using linear regression using “SNPassoc” package from R statistical software. Using an additive genetic model, linear regression analysis showed the T-allele of rs1534649 to be associated with increased BMI in a dose-dependent trend β = 2.13 (95% CI 1.33–2.94); p = 1.7 × 10⁻⁷. In addition, a borderline significance was observed between the T-allele and low levels of high density lipoprotein-cholesterol β = −0.04 (95% CI −0.08, −0.006); p = 0.02. There were no associations between rs28645722 and plasma lipid levels (p > 0.05). However, a trend was observed between the A-allele and increased BMI β = 1.75 (95% CI 0.14–3.35); p = 0.03. Our study shows intron one polymorphism rs1534649 to increase the risk of obesity and dyslipidemia. Our findings warrant further investigation of the mechanism of LPL on the development of obesity along with the role of intron one and its impact on LPL gene activity.

Relationships of Cerebrospinal Fluid Alzheimer's Disease Biomarkers and COMT, DBH, and MAOB Single Nucleotide Polymorphisms

The noradrenergic and dopaminergic systems are affected in Alzheimer’s disease (AD). Polymorphisms in genes encoding enzymes and proteins that are components of these systems can affect products of transcription and translation and lead to altered enzymatic activity and alterations in overall dopamine and noradrenaline levels. Catechol-O-methyltransferase (COMT) and monoamine oxidase B (MAOB) are the enzymes that regulate degradation of dopamine, while dopamine β-hydroxylase (DBH) is involved in synthesis of noradrenaline. COMT Val158Met (rs4680), DBH rs1611115 (also called –1021C/T or –970C/T), and MAOB rs1799836 (also called A644G) polymorphisms have been previously associated with AD. We assessed whether these polymorphisms are associated with cerebrospinal fluid (CSF) AD biomarkers including total tau (t-tau), phosphorylated tau proteins (p-tau₁₈₁, p-tau₁₉₉, and p-tau₂₃₁), amyloid-β₄₂ (Aβ₄₂), and visinin-like protein 1 (VILIP-1) to test possible relationships of specific genotypes and pathological levels of CSF AD biomarkers. The study included 233 subjects: 115 AD, 53 mild cognitive impairment, 54 subjects with other primary causes of dementia, and 11 healthy controls. Significant decrease in Aβ₄₂ levels was found in patients with GG compared to AG COMT Val158Met genotype, while t-tau and p-tau₁₈₁ levels were increased in patients with AA compared to AG COMT Val158Met genotype. Aβ₄₂ levels were also decreased in carriers of A allele in MAO-B rs1799836 polymorphism, while p-tau₁₈₁ levels were increased in carriers of T allele in DBH rs1611115 polymorphism. These results indicate that COMT Val158Met, DBH rs1611115, and MAOB rs1799836 polymorphisms deserve further investigation as genetic markers of AD.

Eckel R. Genetic Variants of Lipoprotein Lipase and Regulatory Factors Associated with Alzheimer's Disease Risk

Lipoprotein lipase (LPL) is a key enzyme in lipid and lipoprotein metabolism. The canonical role of LPL involves the hydrolysis of triglyceride-rich lipoproteins for the provision of FFAs to metabolic tissues. However, LPL may also contribute to lipoprotein uptake by acting as a molecular bridge between lipoproteins and cell surface receptors. Recent studies have shown that LPL is abundantly expressed in the brain and predominantly expressed in the macrophages and microglia of the human and murine brain. Moreover, recent findings suggest that LPL plays a direct role in microglial function, metabolism, and phagocytosis of extracellular factors such as amyloid- beta (Aβ). Although the precise function of LPL in the brain remains to be determined, several studies have implicated LPL variants in Alzheimer's disease (AD) risk. For example, while mutations shown to have a deleterious effect on LPL function and expression (e.g., N291S, HindIII, and PvuII) have been associated with increased AD risk, a mutation associated with increased bridging function (S447X) may be protective against AD. Recent studies have also shown that genetic variants in endogenous LPL activators (ApoC-II) and inhibitors (ApoC-III) can increase and decrease AD risk, respectively, consistent with the notion that LPL may play a protective role in AD pathogenesis. Here, we review recent advances in our understanding of LPL structure and function, which largely point to a protective role of functional LPL in AD neuropathogenesis.

Pharmacogenomics of Cognitive Dysfunction and Neuropsychiatric Disorders in Dementia

Symptomatic interventions for patients with dementia involve anti-dementia drugs to improve cognition, psychotropic drugs for the treatment of behavioral disorders (BDs), and different categories of drugs for concomitant disorders. Demented patients may take >6–10 drugs/day with the consequent risk for drug–drug interactions and adverse drug reactions (ADRs >80%) which accelerate cognitive decline. The pharmacoepigenetic machinery is integrated by pathogenic, mechanistic, metabolic, transporter, and pleiotropic genes redundantly and promiscuously regulated by epigenetic mechanisms. CYP2D6, CYP2C9, CYP2C19, and CYP3A4/5 geno-phenotypes are involved in the metabolism of over 90% of drugs currently used in patients with dementia, and only 20% of the population is an extensive metabolizer for this tetragenic cluster. ADRs associated with anti-dementia drugs, antipsychotics, antidepressants, anxiolytics, hypnotics, sedatives, and antiepileptic drugs can be minimized by means of pharmacogenetic screening prior to treatment. These drugs are substrates, inhibitors, or inducers of 58, 37, and 42 enzyme/protein gene products, respectively, and are transported by 40 different protein transporters. APOE is the reference gene in most pharmacogenetic studies. APOE-3 carriers are the best responders and APOE-4 carriers are the worst responders; likewise, CYP2D6-normal metabolizers are the best responders and CYP2D6-poor metabolizers are the worst responders. The incorporation of pharmacogenomic strategies for a personalized treatment in dementia is an effective option to optimize limited therapeutic resources and to reduce unwanted side-effects.

Alpha-2-Macroglobulin, a Hypochlorite-Regulated Chaperone and Immune System Modulator

Alpha-macroglobulins are ancient proteins that include monomeric, dimeric, and tetrameric family members. In humans, and many other mammals, the predominant alpha-macroglobulin is alpha-2-macroglobulin (α₂M), a tetrameric protein that is constitutively abundant in biological fluids (e.g., blood plasma, cerebral spinal fluid, synovial fluid, ocular fluid, and interstitial fluid). α₂M is best known for its remarkable ability to inhibit a broad spectrum of proteases, but the full gamut of its activities affects diverse biological processes. For example, α₂M can stabilise and facilitate the clearance of the Alzheimer's disease-associated amyloid beta (Aβ) peptide. Additionally, α₂M can influence the signalling of cytokines and growth factors including neurotrophins. The results of several studies support the idea that the functions of α₂M are uniquely regulated by hypochlorite, an oxidant that is generated during inflammation, which induces the native α₂M tetramer to dissociate into dimers. This review will discuss the evidence for hypochlorite-induced regulation of α₂M and the possible implications of this in neuroinflammation and neurodegeneration.

Human pregnancy zone protein stabilizes misfolded proteins including preeclampsia- and Alzheimer's-associated amyloid beta peptide

Pregnancy is a unique physiological state involving biological stresses that promote protein damage (misfolding) within the maternal body. Currently, little is known regarding how the maternal body copes with elevated protein misfolding in pregnancy. This is important, because the accumulation of misfolded proteins underlies many human disorders, including preeclampsia, a serious complication of pregnancy. In this study, we show that pregnancy zone protein (PZP) efficiently inhibits the aggregation of misfolded proteins, including the amyloid beta peptide, which forms plaques in preeclampsia and in Alzheimer’s disease. We propose that up-regulation of PZP is a major maternal adaptation that helps to maintain protein homeostasis during pregnancy. Moreover, pregnancy-independent up-regulation of PZP indicates that its chaperone function could be broadly important in humans.

Protein misfolding underlies the pathology of a large number of human disorders, many of which are age-related. An exception to this is preeclampsia, a leading cause of pregnancy-associated morbidity and mortality in which misfolded proteins accumulate in body fluids and the placenta. We demonstrate that pregnancy zone protein (PZP), which is dramatically elevated in maternal plasma during pregnancy, efficiently inhibits in vitro the aggregation of misfolded proteins, including the amyloid beta peptide (Aβ) that is implicated in preeclampsia as well as with Alzheimer’s disease. The mechanism by which this inhibition occurs involves the formation of stable complexes between PZP and monomeric Aβ or small soluble Aβ oligomers formed early in the aggregation pathway. The chaperone activity of PZP is more efficient than that of the closely related protein alpha-2-macroglobulin (α₂M), although the chaperone activity of α₂M is enhanced by inducing its dissociation into PZP-like dimers. By immunohistochemistry analysis, PZP is found primarily in extravillous trophoblasts in the placenta. In severe preeclampsia, PZP-positive extravillous trophoblasts are adjacent to extracellular plaques containing Aβ, but PZP is not abundant within extracellular plaques. Our data support the conclusion that the up-regulation of PZP during pregnancy represents a major maternal adaptation that helps to maintain extracellular proteostasis during gestation in humans. We propose that overwhelming or disrupting the chaperone function of PZP could underlie the accumulation of misfolded proteins in vivo. Attempts to characterize extracellular proteostasis in pregnancy will potentially have broad-reaching significance for understanding disease-related protein misfolding.

Lipoprotein lipase: new roles for an 'old' enzyme

PURPOSE OF REVIEW

Lipoprotein lipase (LpL) is well known for its lipolytic action in blood lipoprotein triglyceride catabolism. This article summarizes the recent mechanistic and molecular studies on elucidating the 'unconventional' roles of LpL in mediating biological events related to immune cell response and lipid transport in the pathogenesis of cardiovascular disease (CVD) and tissue degenerative disorders.

RECENT FINDINGS

Several approaches to inactivate the inhibitors that block LpL enzymatic activity have reestablished the importance of systemic LpL activity in reducing CVD risk. On the other hand, increasing evidence suggests that focal arterial expression of LpL relates to aortic macrophage levels and inflammatory processes. In the hematopoietic origin, LpL also plays a role in modulating hematopoietic stem cell proliferation and circulating blood cell levels and phenotypes. Finally, building upon the strong genetic evidence on the association with assorted brain disorders, a new era in exploring the mechanistic insights into the functions and activity of LpL in brain that impacts central nerve systems has begun.

SUMMARY

A better understanding of the molecular action of LpL will help to devise novel strategies for intervention of a number of diseases, including blood cell or metabolic disorders, as well to inhibit pathways related to CVD and tissue degenerative processes.

ATP-binding cassette transporter-2 (ABCA2) as a therapeutic target

The ATP binding cassette transporter ABCA2 is primarily an endolysosomal membrane protein that demonstrates pleiotropic functionalities, coalescing around the maintenance of homeostasis of sterols, sphingolipids and cholesterol. It is most highly expressed in brain tissue and ABCA2 knockout mice express neurological defects consistent with aberrant myelination. Increased expression of the transporter has been linked with resistance to cancer drugs, particularly those possessing a steroid backbone and gene expression (in concert with other genes involved in cholesterol metabolism) was found to be regulated by sterols. Moreover, in macrophages ABCA2 is influenced by sterols and has a role in regulating cholesterol sequestration, potentially important in cardiovascular disease. Accumulating data indicate the critical importance of ABCA2 in mediating movement of sphingolipids within cellular compartments and these have been implicated in various aspects of cholesterol trafficking. Perhaps because the functions of ABCA2 are linked with membrane building blocks, there are reports linking it with human pathologies, including, cholesterolemias and cardiovascular disease, Alzheimer's and cancer. The present review addresses whether there is now sufficient information to consider ABCA2 as a plausible therapeutic target.

Multiscale network modeling of oligodendrocytes reveals molecular components of myelin dysregulation in Alzheimer's disease

BACKGROUND

Oligodendrocytes (OLs) and myelin are critical for normal brain function and have been implicated in neurodegeneration. Several lines of evidence including neuroimaging and neuropathological data suggest that Alzheimer's disease (AD) may be associated with dysmyelination and a breakdown of OL-axon communication.

METHODS

In order to understand this phenomenon on a molecular level, we systematically interrogated OL-enriched gene networks constructed from large-scale genomic, transcriptomic and proteomic data obtained from human AD postmortem brain samples. We then validated these networks using gene expression datasets generated from mice with ablation of major gene expression nodes identified in our AD-dysregulated networks.

RESULTS

The robust OL gene coexpression networks that we identified were highly enriched for genes associated with AD risk variants, such as BIN1 and demonstrated strong dysregulation in AD. We further corroborated the structure of the corresponding gene causal networks using datasets generated from the brain of mice with ablation of key network drivers, such as UGT8, CNP and PLP1, which were identified from human AD brain data. Further, we found that mice with genetic ablations of Cnp mimicked aspects of myelin and mitochondrial gene expression dysregulation seen in brain samples from patients with AD, including decreased protein expression of BIN1 and GOT2.

CONCLUSIONS

This study provides a molecular blueprint of the dysregulation of gene expression networks of OL in AD and identifies key OL- and myelination-related genes and networks that are highly associated with AD.

Genetic Association of CHAT rs3810950 and rs2177369 Polymorphisms with the Risk of Alzheimer's Disease: A Meta-Analysis

Choline acetyltransferase (CHAT) rs3810950 and rs2177369 polymorphisms have been implicated in susceptibility to Alzheimer's disease (AD). Due to the inconsistent results from previous studies, a meta-analysis was performed to estimate the association between these polymorphisms and AD risk more precisely. Pooled results of our meta-analysis indicated CHAT rs2177369 polymorphism was correlated with decreasing AD risk in one of five genetic models (dominant: OR = 0.77, 95% CI: 0.62–0.96), while rs3810950 mutant was associated with AD development in three models (allelic: OR = 1.18, 95% CI: 1.01–1.37, homozygous: OR = 1.63, 95% CI: 1.09–2.42, and recessive: OR = 1.65, 95% CI: 1.20–2.26). In subgroup analysis by ethnicity, the association between CHAT rs3810950 polymorphism and AD risk was just found in the recessive model (OR = 1.47, 95% CI: 1.05–2.07) among Caucasians, while four genetic models (allelic: OR = 1.23, 95% CI: 1.01–1.48; homozygous: OR = 2.24, 95% CI: 1.48–3.39; dominant: OR = 1.21, 95% CI: 1.06–1.40; and recessive: OR = 2.18, 95% CI: 1.45–3.29) assumed this association in Asians. In conclusion, our meta-analysis indicated CHAT rs2177369 polymorphism might play a protective role in AD, while rs3810950 variant was a risk factor for AD but its single heterozygous mutations might not influence susceptibility to AD.

Influence of Alpha-2-Macroglobulin 5 bp I/D and Ile1000Val polymorphisms on the susceptibility of Alzheimer's disease: a systematic review and meta-analysis of 52 studies

Accumulating studies have evaluated the association of Alpha-2-Macroglobulin gene (A2M) 5 bp insertion/deletion (5 bp I/D, rs3832852) and Ile1000Val (rs669) polymorphisms with Alzheimer's disease (AD) risk, but the results remain inconclusive. To investigate whether these two polymorphisms facilitate the susceptibility to AD, we conducted a comprehensive systematic review and meta-analysis. Databases of PubMed, Embase, Web of Science, Medline, CNKI, and Google Scholar were searched to get the genetic association studies. All statistical analyses were conducted with Review Manager 5.2 and STATA11.0. Fifty-two articles were included in the final meta-analysis. We performed meta-analysis of 39 studies involving 8,267 cases and 7,932 controls for the 5 bp I/D polymorphism and 27 studies involving 6,585 cases and 6,637 controls for the Ile/Val polymorphism. Overall results did not show significant association between these two polymorphisms and AD risk in dominant, recessive, and multiplicative genetic models. On the stratification analyses by ethnicity and APOE ε4 status with genotypes of polymorphism sites, similar negative associations were found. The meta-analysis suggests that there is no enough evidence for associations of A2M gene polymorphisms (5 bp I/D, Ile1000Val) with AD risk at present, even after stratification by ethnicity and APOE ε4 with genotypes of polymorphism sites. However, due to the heterogeneity in the meta-analysis, the results should be interpreted with caution.

Pharmacogenetic Study on the Impact of Rivastigmine Concerning Genetic Variants of A2M and IL-6 Genes on Iranian Alzheimer's Patients

Alzheimer's disease (AD) is a polygenic and multifactorial disease with a complex inheritance caused by the formation of amyloid plaques and neurofibrillary tangles in the brain. Increasing evidence indicates that many genes including interleukin-6 (IL-6) and alpha 2-macroglobulin (A2M) may contribute to the pathogenesis of AD. The A2M gene encodes α2-macroglobulin which specifically binds with the beta-amyloid peptides and prevents fibril formation. Protein of the IL-6 gene linked to beta-amyloid (βA) aggregation was detected in βA plaques in the brain of AD patients. The aim of the present study is to investigate the relationship of the IL-6 and A2M gene polymorphisms with AD and also the impact of rivastigmine on AD patients regarding their genotypes on IL-6 and A2M genes in 150 Iranian AD patients under rivastigmine therapy and 150 matched healthy controls. The results indicated that IL-6 G and C alleles had significant positive and negative association with AD, respectively, (P = 0.0001, relative risks (RR) = 1.39) and frequency of AD patients carrying IL-6 GG genotype was significantly in higher proportion in familial Alzheimer's disease (FAD) patients compared to controls (P = 0.02, RR = 2.25), and the IL-6 CC genotype was significantly protective against AD (P = 0.0003, RR = 0.65). Genotype analysis of A2M gene showed a significant positive correlation between A2M AA genotype and the AD patients (sporadic Alzheimer's disease (SAD) and FAD) (P = 0.001, RR = 1.56), proposing it as a possible risk factor for AD. Drug response from pharmacogenetic viewpoint after 3-year follow-up of AD patients and Clinical Dementia Rating (CDR) analysis demonstrated that AD patients carrying bigenic genotype IL-6 CC-A2M AG (ΔCDR = 4.5) and male patients with IL-6 CC genotype (ΔCDR = 3.83) provided the best response and the A2M GG genotype (ΔCDR = 7.97) and bigenic genotype IL-6 GG-A2M GG (ΔCDR = 8.5) conferred the worst response to the rivastigmine, suggesting likely involvement of genotype-specific response to rivastigmine therapy in AD patients. The results also propose that in view of the fact that C and G alleles created by nucleotide changes in the promoter region of IL-6 gene and this may affect the expression of the IL-6 gene and, hence, susceptible and protective role of GG and CC genotype in AD might be caused by higher and lower expression of IL-6 cytokine, respectively.

OPRK1 promoter hypermethylation increases the risk of Alzheimer's disease

As a member of the opioid family, κ-opioid receptors play important role in cognitive and learning functions. The purpose of this study was to evaluate the association of OPRK1 promoter methylation with Alzheimer's disease (AD). OPRK1 DNA methylation levels of 48 cases and 58 well matched controls were measured using the bisulphite pyrosequencing technology. Our results showed that there was a significant correlation between three CpG sites on the OPRK1 promoter region (r>=0.715, p<0.001). Thus, the mean methylation value of the three CpG sites was used for the case-control comparison. And our results showed there was a significantly higher OPRK1 promoter methylation in AD cases than in controls (p=0.006, adjusted p=0.012). Subsequent luciferase reporter assay showed the CpGs containing fragment of OPRK1 promoter significantly increased the expression of reporter gene (Fold=2.248, p=0.0235). In summary, our results suggested that OPRK1 promoter hypermethylation might increase the risk of AD through its regulation on the gene expression of OPRK1.

Association of BDNF and BCHE with Alzheimer's disease: Meta-analysis based on 56 genetic case-control studies of 12,563 cases and 12,622 controls

Alzheimer's disease (AD) is a common neurodegenerative disorder that can destroy the memory of sufferers and lead to distress for the individual and society. Brain-derived neurotrophic factor (BDNF) and butyrylcholinesterase (BCHE) are two genes associated with β-amyloid plaques and neurofibrillary tangles that are two key factors in the pathophysiology of AD. The aim of the current meta-analysis was to evaluate the association between BDNF Val66Met (rs6265), BDNF C270T (rs2030324) and BCHE-K (rs1803274) polymorphisms and AD. A comprehensive meta-analysis was performed using the online database PubMed without a time limitation. A total of 56 articles evaluating 12,563 cases and 12,622 controls were selected for the current meta-analysis. The results showed a moderate association of the BDNF C270T polymorphism with the risk of AD in Asians under a dominant model (P=0.03; odds ratio, 1.88; 95% confidence interval, 1.08-3.27). No other significant association was found during the meta-analysis for the other two polymorphisms (P>0.05). The current meta-analysis suggests that BDNF C270T is a risk factor for AD in Asians. This meta-analysis has been, to the best of our knowledge, the most comprehensive meta-analysis of BDNF Val66Met, BDNF C270T and BCHE-K to date.

Elevation of peripheral BDNF promoter methylation links to the risk of Alzheimer's disease

Brain derived neurotrophic factor (BDNF) has been known to play an important role in various mental disorders or diseases such as Alzheimer's disease (AD). The aim of our study was to assess whether BDNF promoter methylation in peripheral blood was able to predict the risk of AD. A total of 44 AD patients and 62 age- and gender-matched controls were recruited in the current case-control study. Using the bisulphite pyrosequencing technology, we evaluated four CpG sites in the promoter of the BDNF. Our results showed that BDNF methylation was significantly higher in AD cases than in the controls (CpG1: p = 10.021; CpG2: p = 0.002; CpG3: p = 0.007; CpG4: p = 0.005; average methylation: p = 0.004). In addition, BDNF promoter methylation was shown to be significantly correlated with the levels of alkaline phosphatase (ALP), glucose, Lp(a), ApoE and ApoA in males (ALP: r = -0.308, p = 0.042; glucose: r = -0.383, p = 0.010; Lp(a): r = 0.333, p = 0.027; ApoE: r = -0.345, p = 0.032;), ApoA levels in females (r = 0.362, p = 0.033), and C Reactive Protein (CRP) levels in both genders (males: r = -0.373, p = 0.016; females: r = -0.399, p = 0.021). Our work suggested that peripheral BDNF promoter methylation might be a diagnostic marker of AD risk, although its underlying function remains to be elaborated in the future.

Association between LGALS2 3279C>T and coronary artery disease: A case-control study and a meta-analysis

Coronary artery disease (CAD) has become the main cause of mortality worldwide. Lectin galactoside-binding soluble-2 (LGALS2) is involved in the cytokine lymphotoxin-α (LTA) cascade that may influence the progress of CAD. The aim of the present study was to assess the association between the LGALS2 3279C>T (rs7291467) polymorphism and CAD. A total of 562 cases and 572 controls were recruited to examine the association. A systematic meta-analysis was performed to evaluate the contribution of LGALS2 3279C>T polymorphism to the risk of CAD among 12,093 cases and 11,020 controls. There was no significant association found in the present case-control study. However, the meta-analysis showed that LGALS2 3279C>T played a protective role in CAD [P=0.008, odds ratio (OR), 0.90; 95% confidence interval (95% CI), 0.82-0.97] and particularly in the Asian population (P=0.006; OR, 0.82; 95% CI, 0.71-0.94). The present case-control study did not find a significant association between LGALS2 3279C>T and CAD in the Eastern Han Chinese population. However, the meta-analysis indicated that LGALS2 3279C>T played a protective role in CAD, suggesting an ethnic difference in the association of the locus with CAD.

Meta-analyses of seven GIGYF2 polymorphisms with Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder that affects ~2% of the global population aged ≥65 years. Grb10-interacting GYF protein-2 (GIGYF2) can influence the development of PD through the regulation of insulin-like growth factor-1. The aim of the present meta-analysis study was to establish the contribution of GIGYF2 polymorphisms to PD. The study was conducted based on nine eligible studies consisting of 7,246 PD patients and 7,544 healthy controls. The results indicated that the GIGYF2 C.3630A>G polymorphism increased the risk of PD by 37% [P=0.008; odds ratio (OR), 1.37; 95% confidence interval (CI), 1.08-1.73] and that the GIGYF2 C.167G>A polymorphism was significantly associated with PD (P=0.003; OR, 3.67; 95% CI, 1.56-8.68). The meta-analyses of the other five GIGYF2 polymorphisms (C.1378C>A, C.1554G>A, C.2940A>G, C.1370C>A and C.3651G>A) did not reveal any significant associations. The present meta-analyses of the GIGYF2 genetic polymorphisms may provide a comprehensive overview of this PD candidate gene for future studies.

Association study of two steroid biosynthesis genes (COMT and CYP17) with Alzheimer's disease in the Italian population

The greater predisposition of women to Alzheimer's disease (AD), owing to the decrease in postmenopausal estrogen, may be influenced by polymorphic variation in genes regulating estrogen metabolism (e.g., COMT) and estrogen biosynthesis (e.g., CYP17). In order to better understand how the estrogen pathway genetic variation might affect AD onset, we conducted a case-control study of two single nucleotide polymorphisms (SNPs) of these two genes (COMT rs4680 and CYP17 rs743572) in a sample of AD patients of Italian origin. The COMT allele and genotype were found associated neither with AD onset nor with parameters of AD severity, such as cognitive impairment, age at onset, or disease duration. In contrast, CYP17 was found to affect the age at disease onset mainly in males and, as compared with noncarriers, people carrying the A2 (C) allele had a 2.2-fold increased risk for AD. These findings suggest that the CYP17 A2 allele influences AD susceptibility in a sex-specific way by acting not only on AD risk but also on the age at disease onset, an important parameter of AD severity.

Association of NQO1 and TNF polymorphisms with Parkinson's disease: A meta-analysis of 15 genetic association studies

Parkinson's disease (PD) is a neurodegenerative movement d'isorder that affects ~2% of the population aged ≥65 years. NAD(P)H-quinone oxidoreductase 1 (NQO1) and tumor necrosis factor-α (TNF-α) are two important factors in the generation of oxidative stress in PD. The aim of the present study was to assess the association of NQO1 and tumor necrosis factor (TNF) polymorphisms with PD. A meta-analysis was performed that included data from 15 studies comprising 2,858 patients and 2,907 healthy controls. The results showed that TNF-1031 (rs1799964) was significantly associated with PD in the recessive [P=0.0005; odds ratio (OR), 3.19; 95% confidence interval (CI), 1.66-6.13] and additive models (P=0.0006; OR, 3.15; 95% CI, 1.63-3.51). However, there was no significant association in NQO1 C609T (rs1800566) and TNF-308 (rs1800629) with PD. To the best of our knowledge, the present study is the first meta-analysis of NQO1 and TNF polymorphisms with PD demonstrating that TNF-1031 polymorphism may be a risk factor for PD under either the recessive or additive models. However, the meta-analyses did not support the involvement of NQO1 C609T and TNF-308 in the risk of PD.