Lack of replication of association findings in complex disease: an analysis of 15 polymorphisms in prior candidate genes for sporadic 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.

Presubiculum principal cells are preserved from degeneration in knock-in APP/TAU mouse models of Alzheimer's disease

The presubiculum (PRS) is an integral component of the perforant pathway that has recently been recognised as a relatively unscathed region in clinical Alzheimer's disease (AD), despite neighbouring components of the perforant pathway, CA1 and the entorhinal cortex, responsible for formation of episodic memory and storage, showing severe hallmarks of AD including, amyloid-beta (Aβ) plaques, tau tangles and marked gliosis. However, the question remains whether this anatomical resilience translates into functional resilience of the PRS neurons. Using neuroanatomy combined with whole-cell electrophysiological recordings, we investigated whether the unique spatial profile of the PRS was replicable in two knock-in mouse models of AD, APPNL-F/NL-F, and APPNL-F/MAPTHTAU and whether the intrinsic properties and morphological integrity of the PRS principal neurons was maintained compared to the lateral entorhinal cortex (LEC) and hippocampal CA1 principal cells. Our data revealed an age-dependent Aβ and tau pathology with neuroinflammation in the LEC and CA1, but a presence of fleece-like Aβ deposits with an absence of tau tangles and cellular markers of gliosis in the PRS of the mouse models at 11-16 and 18-22 months. These observations were consistent in human post-mortem AD tissue. This spatial profile also correlated with functional resilience of strong burst firing PRS pyramidal cells that showed unaltered sub- and suprathreshold intrinsic biophysical membrane properties and gross morphology in the AD models that were similar to the properties of pyramidal cells recorded in age-matched wild-type mice (11-14 months). This was in contrast to the LEC and CA1 principal cells which showed altered subthreshold intrinsic properties such as a higher input resistance, longer membrane time constants and hyperexcitability in response to suprathreshold stimulation that correlated with atrophied dendrites in both AD models. In conclusion, our data show for the first time that the unique anatomical profile of the PRS constitutes a diffuse AD pathology that is correlated with the preservation of principal pyramidal cell intrinsic biophysical and morphological properties despite alteration of LEC and CA1 pyramidal cells in two distinct genetic models of AD. Understanding the underlying mechanisms of this resilience could be beneficial in preventing the spread of disease pathology before cognitive deficits are precipitated in AD.

Angiotensin-converting enzyme polymorphisms AND Alzheimer's disease susceptibility: An updated meta-analysis

Background

Many studies among different ethnic populations suggested that angiotensin converting enzyme (ACE) gene polymorphisms were associated with susceptibility to Alzheimer’s disease (AD). However, the results remained inconclusive. In the present meta-analysis, we aimed to clarify the effect of ACE polymorphisms on AD risk using all available relevant data.

Methods

Systemic literature searches were performed using PubMed, Embase, Alzgene and China National Knowledge Infrastructure (CNKI). Relevant data were abstracted according to predefined criteria.

Results

Totally, 82 independent cohorts from 65 studies were included, focusing on five candidate polymorphisms. For rs1799752 polymorphism, in overall analyses, the insertion (I) allele conferred increased risk to AD compared to the deletion (D) allele (I vs. D: OR = 1.091, 95% CI = 1.007–1.181, p = 0.032); while the I carriers showed increased AD susceptibility compared with the D homozygotes (II + ID vs. DD: OR = 1.131, 95% CI = 1.008–1.270, p = 0.036). However, none of the positive results passed FDR adjustment. In subgroup analysis restricted to late-onset individuals, the associations between rs1799752 polymorphism and AD risk were identified using allelic comparison (OR = 1.154, 95% CI = 1.028–1.295, p = 0.015, FDR = 0.020), homozygotes comparison, dominant model and recessive model (II vs. ID + DD: OR = 1.272, 95% CI = 1.120–1.444, p < 0.001, FDR < 0.001). Nevertheless, no significant association could be revealed after excluding studies not in accordance with Hardy-Weinberg equilibrium (HWE). In North Europeans, but not in East Asians, the I allele demonstrated increased AD susceptibility compared to the D allele (OR = 1.096, 95% CI = 1.021–1.178, p = 0.012, FDR = 0.039). After excluding HWE-deviated cohorts, significant associations were also revealed under homozygotes comparison, additive model (ID vs. DD: OR = 1.266, 95% CI = 1.045–1.534, p = 0.016, FDR = 0.024) and dominant model (II + ID vs. DD: OR = 1.197, 95% CI = 1.062–1.350, p = 0.003, FDR = 0.018) in North Europeans. With regard to rs1800764 polymorphism, significant associations were identified particularly in subgroup of European descent under allelic comparison (T vs. C: OR = 1.063, 95% CI = 1.008–1.120, p = 0.023, FDR = 0.046), additive model and dominant model (TT + TC vs. CC: OR = 1.116, 95% CI = 1.018–1.222, p = 0.019, FDR = 0.046). But after excluding studies not satisfying HWE, all these associations disappeared. No significant associations were detected for rs4343, rs4291 and rs4309 polymorphisms in any genetic model.

Conclusions

Our results suggested the significant but modest associations between rs1799752 polymorphism and risk to AD in North Europeans. While rs4343, rs4291 and rs4309 polymorphisms are unlikely to be major factors in AD development in our research.

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.

IL-1β, IL-6, IL-10, and TNFα Single Nucleotide Polymorphisms in Human Influence the Susceptibility to Alzheimer's Disease Pathology

BACKGROUND

Neuroinflammation plays an important role in Alzheimer's disease (AD). During this process, activated microglia release pro-inflammatory cytokines such as interleukin (IL)-1α, IL-1β, IL-6, and tumor necrosis factor α (TNFα) that participate in neuron damage, but also anti-inflammatory cytokines (such as IL-10), which maintain homeostasis of immune response. Previous studies showed the association of IL-1α -889C/T (rs1800587), IL-1β-1473G/C (rs1143623), IL-6 -174C/G (rs1800795), IL-10 -1082G/A (rs1800896), and TNFα -308A/G (rs1800629) polymorphisms with AD.

OBJECTIVE

We aimed to investigate whether people with certain IL-1α, IL-1β, IL-6, IL-10, and TNFα genotypes in these polymorphisms are more prone to develop AD-related pathology, reflected by pathological levels of cerebrospinal fluid (CSF) AD biomarkers including amyloid-β1-42, total tau (t-tau), tau phosphorylated at Thr 181 (p-tau181), Ser 199 (p-tau199), and Thr 231 (p-tau231), and visinin-like protein 1 (VILIP-1).

METHODS

The study included 115 AD patients, 53 patients with mild cognitive impairment, and 11 healthy controls. The polymorphisms were determined using real-time polymerase chain reaction. Levels of CSF biomarkers were determined by enzyme-linked immunosorbent assay.

RESULTS

A significant increase in p-tau CSF levels was found in patients with the AA IL-10 -1082G/A and GG TNFα -308A/G genotypes, and in carriers of a G allele in IL-1β -1473C/G and IL-6 -174C/G polymorphisms. t-tau levels were increased in carriers of a G allele in IL-1β -1473C/G polymorphism. An increase in VILIP-1 levels was observed in patients with CG and GG IL-1β -1473C/G, GC IL-6 -174C/G, and GG TNFα -308A/G genotype.

CONCLUSION

These results suggest that persons carrying certain genotypes in IL10 (-1082G/A), IL1β (1473C/G), IL6 (-174C/G), and TNFIα (-308A/G) could be more vulnerable to development of neuroinflammation, and consequently of AD.

Pharmacogenetic analyses of variations of measures of cardiovascular risk in Alzheimer's dementia

Background & objectives:

Neurodegeneration affects blood pressure variations, while renal function and cerebral perfusion are impaired by vascular risk factors. This study was aimed to estimate variations of measures of cardiovascular risk in Alzheimer's dementia by pharmacogenetic analyses of the effects of angiotensin-converting enzyme (ACE) inhibitors and statins.

Methods:

Consecutive patients were prospectively followed to study variations of creatinine clearance and blood pressure for one year, estimated by correlating the effects of ACE inhibitors with the ACE Alu I/D polymorphism and genotypes or haplotypes of rs1800764 or rs4291, and the effects of statins with LDLR (low-density lipoprotein receptor) genotypes or haplotypes of rs11669576 (exon 8) or rs5930 (exon 10), or genotypes of rs2695121 (liver X receptor β gene). Variations of the coronary heart disease (CHD) risk according to these cardiovascular measures were also explored.

Results:

All polymorphisms of the 193 patients were in Hardy-Weinberg equilibrium. Genetic determinants of cardiovascular effects affected the individual variability of the response to ACE inhibitors and statins. ACE inhibitors, but not statins, reduced blood pressure for all patients. ACE inhibitors protected carriers of alleles that supposedly decrease serum ACE levels (rs1800764-T, rs4291-A, Alu II) regarding creatinine clearance variations (P<0.005), but carriers of Alu DD (P<0.02), rs1800764-C (P<0.05), or rs4291-AT (P<0.04) showed better blood pressure lowering effects. The presence of rs2695121-T (P=0.007) or rs5930-A (P=0.039) was associated with systolic blood pressure lowering, whereas rs5930-AA was protective against decrease in creatinine clearance (P=0.019). Statins lowered creatinine clearance for carriers of rs2695121-CT (P=0.026).

Interpretation & conclusions:

Pharmacological response of blood pressure and creatinine clearance to ACE inhibitors and statins may be genetically mediated.

The C677T Polymorphism of the Methylenetetrahydrofolate Reductase Gene and Susceptibility to Late-onset Alzheimer's Disease

Folate metabolism makes a crucial contribution towards late-onset Alzheimer's disease (LOAD). Moreover, methylenetetrahydrofolate reductase (MTHFR) constitutes the primary enzyme of the folate pathway. We hypothesize that there is an association of C677T polymorphism in the MTHFR gene with the susceptibility to LOAD. Previous published research has investigated the link between the MTHFR C677T polymorphisms and LOAD susceptibility; nevertheless, the findings have continued to be not only controversial, but also indecisive. Accordingly, we carried out the present meta-analysis for the assessment of the potential link that exists between the MTHFR C677T polymorphism and the susceptibility to LOAD. Furthermore, we carried out a literature search of the PubMed, EMBASE, Cochrane Library, and WanFang database up to August 10, 2018. The odds ratios (ORs) with the respective 95% confidence interval (95%CI) were put to use for the evaluation of the robustness of the link of the MTHFR C677T polymorphism with the vulnerability to LOAD. All statistical analyses were carried out using STATA 15.0. An aggregate of 14 case-control research works was retrieved, involving 2,467 LOAD patients as well as 2,877 controls. We found that a substantial link exists between C677T polymorphism and LOAD risk in a codominant framework (TC vs. CC: OR=1.22, 95%CI=1.00-1.49, P=0.049). In addition to the stratified analysis based on ethnicity, which suggested that C677T polymorphism was likely linked only to an augmented threat of LOAD in Asians, it did not exist among Caucasians. Furthermore, in the subgroup analysis carried out using APOE ɛ4 status, a substantial increase in the susceptibility to LOAD was detected in APOE ɛ4 carriers as well as non-APOE ɛ4 carriers. In sum, the current meta-analysis revealed that MTHFR C677T polymorphism was associated with susceptibility to LOAD. Further extensive case-control studies are required.

Association between LRP1 C766T polymorphism and Alzheimer's disease susceptibility: a meta-analysis

Low density lipoprotein receptor-related protein 1 (LRP1) C766T polymorphism (rs1799986) has been extensively investigated for Alzheimer’s disease (AD) susceptibility. However, results in different studies have been contradictory. Therefore, we conducted a meta-analysis containing 6455 AD cases and 6304 controls from 26 independent case–control studies to determine whether there was an association between the LRP1 C766T polymorphism and AD susceptibility. The combined analysis showed that there was no significant association between LRP1 C766T polymorphism and AD susceptibility (TT + CT versus CC: OR = 0.920, 95% CI = 0.817–1.037, P = 0.172). In subgroup analysis, significant decreased AD susceptibility was found among Asian population in allele model (T versus C: OR = 0.786, 95% CI = 0.635–0.974, P = 0.028) and dominant model (TT + CT versus CC: OR = 0.800, 95% CI = 0.647–0.990, P = 0.040). Moreover, T allele of LRP1 C766T was statistically associated with late onset of AD (LOAD) (T versus C: OR = 0.858, 95% CI = 0.748–0.985, P = 0.029; TT + CT versus CC: OR = 0.871, 95% CI = 0.763–0.994, P = 0.040). In conclusion, our meta-analysis suggested that LRP1 C766T polymorphism was associated with lower risk of AD in Asian, and could reduce LOAD risk especially. Considering some limitations of our meta-analysis, further large-scale studies should be done to reach a more comprehensive understanding.

PSEN1 gene polymorphisms in Caucasian Alzheimer's disease: A meta-analysis

BACKGROUND

A meta-analysis was performed to assess PSEN1 gene polymorphisms (rs1800839 and rs17125721) in Alzheimer's disease (AD) risk.

METHODS

A systematic electronic search was performed across databases to retrieve studies published before 31 January 2017. The association between the selected PSEN1 polymorphisms and AD was based on five genetic models using DerSimonian and Laird's method or Mantel-Haenszel's method.

RESULTS

A total of 14 case-controlled studies were included. Results showed that rs1800839 polymorphism was significantly associated with AD in allelic OR=0.85 (95% CI [0.72-1.00]) and dominant OR=0.82 (95% CI [0.69-0.98]) genetic models, respectively. However, an insignificant association was found for rs17125721 polymorphism in all genetic models.

CONCLUSIONS

Meta-analysis of PSEN1 gene suggests that the rs1800839 polymorphism has potential influence on AD among Caucasians.

Homocysteine and Alzheimer's Disease: Evidence for a Causal Link from Mendelian Randomization

BACKGROUND/OBJECTIVE

The relationship between plasma homocysteine (Hcy) levels and Alzheimer's disease (AD) has been studied for many years, but remains controversial. While a recent meta-analysis of epidemiological studies, which included observational studies, indicated that homocysteine may be a risk factor for AD, there remains a need to further demonstrate this link due to the large degree of heterogeneity between studies. Epidemiological studies have certain limitations, as their results can be affected by confounding factors and reverse causation. In this study, we evaluated the relationship between plasma homocysteine and AD by using a Mendelian randomization method to avoid problems of confounding bias and reverse causality.

METHODS

We searched the PubMed and EMBASE databases for reports regarding the MTHFR C677T polymorphism (rs1801133) from the time of their inception to September 2015. These reports were combined with related observational studies, and used to evaluate the effect of MTHFR C677T (rs1801133) on the risk for AD. A recent meta-analysis of genome-wide association studies had previously suggested a relationship between homocysteine and MTHFR C677T (rs 1801133).

RESULTS

Our met-analysis included 34 studies with 9397 subjects, and demonstrated a significant relationship between plasma total homocysteine levels and the risk for AD (OR = 3.37; 95% CI = 1.90-5.95; p = 2.9×10-5).

CONCLUSION

Our meta-analysis demonstrated a causal link between plasma total homocysteine and the risk for AD, and provides a new insight into the etiology and prevention of AD.

Potential Links between Impaired One-Carbon Metabolism Due to Polymorphisms, Inadequate B-Vitamin Status, and the Development of Alzheimer's Disease

Alzheimer's disease (AD) is the major cause of dementia and no preventive or effective treatment has been established to date. The etiology of AD is poorly understood, but genetic and environmental factors seem to play a role in its onset and progression. In particular, factors affecting the one-carbon metabolism (OCM) are thought to be important and elevated homocysteine (Hcy) levels, indicating impaired OCM, have been associated with AD. We aimed at evaluating the role of polymorphisms of key OCM enzymes in the etiology of AD, particularly when intakes of relevant B-vitamins are inadequate. Our review indicates that a range of compensatory mechanisms exist to maintain a metabolic balance. However, these become overwhelmed if the activity of more than one enzyme is reduced due to genetic factors or insufficient folate, riboflavin, vitamin B6 and/or vitamin B12 levels. Consequences include increased Hcy levels and reduced capacity to synthetize, methylate and repair DNA, and/or modulated neurotransmission. This seems to favor the development of hallmarks of AD particularly when combined with increased oxidative stress e.g., in apolipoprotein E (ApoE) ε4 carriers. However, as these effects can be compensated at least partially by adequate intakes of B-vitamins, achieving optimal B-vitamin status for the general population should be a public health priority.

Association Between Interleukin-1A, Interleukin-1B, and Bridging integrator 1 Polymorphisms and Alzheimer's Disease: a standard and Cumulative Meta-analysis

Alzheimer's disease (AD) has been one of the most prevalent health problems among senior population. Interleukin-1A (IL-1A) and IL-1B are two isoforms of IL-1. Recent studies suggested that certain polymorphisms on these two genes are associated with AD. Bridging integrator 1 (BIN1) is considered as common genetic risk factors for AD, whereas different studies have provided various conclusions regarding its role in AD. This study was designed to justify the association between multiple gene polymorphisms and AD through an evidence synthesis approach. We conducted a literature search to identify relevant articles published from 2000 to 2015 from PubMed, Embase, and Cochrane Library, in accordance with inclusion criteria. Pooled odds ratios (ORs) were calculated for the allele model. The effect estimates were summarized by both standard and cumulative meta-analysis. Finally, 54 articles with 88 independent studies were enrolled in this meta-analysis. Mutants in rs1800587 of IL-1A, rs1143634 of IL-1B, rs12989701, and rs744373 of BIN1 were significantly associated with AD onset. The difference effect of same single nucleotide polymorphisms (SNPs) on various ethnicities was also observed in our results. The present meta-analysis suggested that IL-1A, IL-1B, and BIN1 were candidate genes for AD pathogenesis. Polymorphisms of IL-1A, IL-1B, and BIN1 are associated with AD onset.

Genetic polymorphisms of interleukin genes and the risk of Alzheimer's disease: An update meta-analysis

Objectives

Recently, several meta-analyses have reported an association between interleukin (IL) gene polymorphisms and the risk of Alzheimer's disease (AD). Several further papers discussing the relationship with the risk of AD have recently been published. The aim of this meta-analysis was to re-evaluate and update the associations between IL gene polymorphisms and the risk of AD.

Methods

The search sources were PubMed, Science Direct, Scopus, and Google Scholar up to July 2015, and the following search terms were used: “interleukin 1 or interleukin 6 or interleukin 10” and “variant or polymorphism or SNP” in combination with “Alzheimer's disease”. A meta-analysis using the pooled odds ratios and 95% confidence intervals was carried out to assess the associations between four polymorphisms of IL genes (− 889C > T in IL-1α, − 511C > T in IL-1β, − 174G > C in IL-6 and − 1082G > A in IL-10) and the risk of AD under the heterozygous, homozygous, dominant, and recessive models with fixed- or random-effects models.

Results

A total of 21,864 cases and 40,321 controls from 93 individual studies were included in this meta-analysis. Our results indicated that the − 889C > T polymorphism was strongly associated with the increased risk of AD. However, three polymorphisms were not associated with the risk of AD.

Conclusions

Similar to previous meta-analyses, our updated meta-analysis suggested that the − 889C > T polymorphism may be a factor in AD. However, the results of our meta-analysis of the − 174G > C polymorphism differed from those of previous meta-analyses. Consequently, we suggest that the − 174G > C polymorphism may not be a risk factor for AD.

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889 C > T polymorphism of IL-1α was significantly associated with increased risk of Alzheimer's disease

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Three polymorphisms (− 511C > T in IL − 1β, − 174G > C in IL-6 and − 1082G > A in IL-10) were no associated with risk of Alzheimer's disease

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The results of our meta-analyses for three polymorphisms (− 889C > T, − 511C > T and − 1082G > A) were similar to those previous meta-analyses. However, the results of the − 174G > C polymorphism were different.

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.

Butyrylcholinesterase K variant and Alzheimer's disease risk: a meta-analysis

Background

Although many studies have estimated the association between the butyrylcholinesterase (BCHE) K variant and Alzheimer’s disease (AD) risk, the results are still controversial. We thus conducted this meta-analysis.

Material/Methods

We searched NCBI, Medline, Web of Science, and Embase databases to find all eligible studies. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the strength of the association.

Results

We found a significant association between BCHE K variant and AD risk (OR=1.20; 95% CI 1.03–1.39; P=0.02). In the stratified analysis by ethnicity, we observed a significant association between BCHE K variant and AD risk in Asians (OR=1.32; 95% CI 1.02–1.72; P=0.04). However, no significant association between BCHE K variant and AD risk in Caucasians was found (OR=1.14; 95% CI 0.95–1.37; P=0.16). When stratified by the age of AD onset, we found that late-onset AD (LOAD) was significantly associated with BCHE K variant (OR=1.44; 95% CI 1.05–1.97; P=0.02). No significant association between BCHE K variant and early-onset AD (EOAD) risk was observed (OR=1.16; 95% CI 0.89–1.51; P=0.27). Compared with non-APOE ɛ4 and non-BCHE K carriers, no significant association between BCHE K variant and AD risk was found (OR=1.11; 95% CI 0.91–1.35; P=0.30). However, APOE ɛ4 carriers showed increased AD risk in both non-BCHE K carriers (OR=2.81; 95% CI 1.75–4.51; P=0.0001) and BCHE K carriers (OR=3.31; 95% CI 1.82–6.02; P=0.0001).

Conclusions

The results of this meta-analysis indicate that BCHE K variant might be associated with AD risk.

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.

The MTHFR C677T polymorphism contributes to increased risk of Alzheimer's disease: evidence based on 40 case-control studies

The association between methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism and Alzheimer's Disease (AD) risk has been widely reported with inconsistent results. We performed an updated meta-analysis of all available studies to clarify this situation. We conducted a comprehensive literature search in PubMed Alzgene, Embase, and Chinese Biomedical Literature database (CBM) for the period up to June 2014. Finally, a total of 40 case-control studies with 4503 AD cases and 5767 controls were included. Overall, significant increased AD risk was found, when all studies were pooled into the meta-analysis. In subgroup analyses stratified by ethnicity, age of onset, and APOE ϵ4 status, significant increased AD risk was found in Asians, late-onset AD, and APOE ϵ4 carriers, but not in Caucasians, early-onset AD, and non-APOE ϵ4 carriers. The present meta-analysis suggested that the MTHFR is a candidate gene for AD susceptibility. The MTHFR C677T polymorphism may be a risk factor for AD in Asians, APOE ϵ4 carriers, and late-onset AD. Further, investigations taking the potential gene-gene and gene-environmental interactions into consideration for the MTHFR C677T polymorphism should be conducted.

Meta-analysis of the association between polymorphisms of estrogen receptor α genes rs9340799 and rs2234693 and Alzheimer's disease: evidence from 23 articles

OBJECTIVE

A meta-analysis was performed to better clarify the association between polymorphisms of estrogen receptor α genes rs9340799 and rs2234693 and risk of Alzheimer's disease (AD).

METHODS

Pooled odds ratios (ORs) with 95% confidence intervals (CIs) from fixed and random effect models were calculated. Heterogeneity among studies was evaluated using the I(2). Meta-regression was used to explore the potential sources of between-study heterogeneity.

RESULTS

A total of 23 studies about rs9340799 and 24 studies about rs2234693 were included in this meta-analysis. The combined evidence suggested that the x allele of rs9340799 had a significant protective effect on the risk of AD in codominant model (ORs = 0.893, 95%CIs = 0.822-0.970), especially for AD in Asia and sporadic AD (SAD). The p allele of rs2234693 was associated with decreased risk of AD in codominant model for patients with SAD. No publication bias was detected.

CONCLUSIONS

This meta-analysis suggested that x allele of rs9340799 might have a protective effect on the risk of AD in Asia and in patients with SAD. In addition, the p allele of rs2234693 might decrease the risk of patients with SAD.

Lack of association between cathepsin D C224T polymorphism and Alzheimer's disease risk: an update meta-analysis

BACKGROUND

Cathepsin D C224T polymorphism has been reported to associate with AD susceptibility. But the results were inconsistent. This study aimed to assess the relationship between C224T polymorphism and AD risk.

METHODS

The relevant studies were identified by searching PubMed, Embase, Web of Science, Google Scholar and Wan fang electronic databases updated on July 2013. The relationship between Cathepsin D C224T polymorphism and AD risk was evaluated by ORs and 95% CIs.

RESULTS

A total of 25 case-control studies including 5,602 cases and 11,049 controls were included in the meta-analysis. There was no association between C224T polymorphism and AD risk with all the studies were pooled in the meta-analysis (CT vs. CC: OR = 1.125, 95% CI = 0.974-1.299, P = 0.109; CT + TT vs. CC: OR = 1.136, 95% CI = 0.978-1.320, P = 0.094). Furthermore, when stratified by ethnicity, age of onset and APOEϵ4 status, significant association did not found in all subgroups.

CONCLUSION

The present meta-analysis suggested that the Cathepsin D C224T polymorphism was not associated with AD susceptibility.

Estrogen receptor α variants affect age at onset of Alzheimer's disease in a multiethnic female cohort

BACKGROUND/AIMS

Few studies of gene variants that affect estrogen activity investigate their association with age at onset of Alzheimer's disease (AD) in women of different ethnicities. We examined the influence of ESR1 polymorphisms on age at onset of AD in a multiethnic cohort of women.

METHODS

Among 1,436 women participating in the Washington Heights Inwood Columbia Aging Project, association with age at AD onset was assessed for 41 single-nucleotide polymorphisms (SNPs) on the ESR1 gene using Cox proportional hazard models, adjusting for presence of an APOE ε4 allele, years of education, and body mass index.

RESULTS

Six SNPs in self-identified White women were protectively associated with delayed age of AD onset in this self-identified group, including the two restriction fragment length polymorphisms PvuII (rs2234693) and XbaI (rs9340799) (HR range = 0.420-0.483). Two separate SNPs were found to affect age of AD onset in self-identified Black women.

CONCLUSIONS

ESR1 polymorphisms affect age of onset of AD in women, and risk alleles vary by ethnicity. These effects are possibly due to different linkage disequilibrium patterns or differences in comorbid environmental or cultural risk factors mediating the SNP effect on risk for AD.

The MTHFR 677T allele may influence the severity and biochemical risk factors of Alzheimer's disease in an Egyptian population

OBJECTIVE

We evaluated whether the methylenetetrahydrofolate reductase (MTHFR) 677C>T marker influences the risk and severity of Alzheimer's disease (AD) and whether AD is associated with homocysteine, vitamin B12, and cholesterol levels in Egypt.

METHODS

Forty-three Alzheimer's cases and 32 non-AD controls were genotyped for the 677C>T polymorphism. Clinical characteristics and levels of homocysteine, vitamin B12, and cholesterol were assessed.

RESULTS

No significant differences in the frequencies of the MTHFR alleles or genotypes between AD cases and controls (P = 0.14) were identified. The 677T mutant allele was significantly overrepresented in AD cases compared to controls (OR = 2.22; P = 0.03). The 677T/T frequency was three times higher in AD patients than in controls, which could increase plasma homocysteine levels. Severe cases of AD were the most frequent in patients with the T/T genotype (11.6%). The effect of the MTHFR polymorphism on the risk of AD may be independent of homocysteine, vitamin B12, or even cholesterol levels.

CONCLUSIONS

The MTHFR 677C>T polymorphism--especially the presence of one copy of the T allele--appears to confer a potential risk for the development of AD. The T/T genotype may contribute to hypercysteinemia as a sensitive marker.

Oestrogen receptor polymorphisms are an associated risk factor for mild cognitive impairment and Alzheimer disease in women APOE {varepsilon}4 carriers: a case-control study

OBJECTIVES

Examine the role of single nucleotide polymorphisms (SNPs) in the oestrogen receptor (ER) genes: rs9340799, rs2234693, rs2228480 (in the ESR1 gene) and rs4986938 (in the ESR2 gene) as a risk factor for amnesic mild cognitive impairment (MCIa) and Alzheimer's disease (AD) and its possible association with the apolipoprotein E (APOE) gene.

DESIGN

We have investigated the independent and combined association of different alleles of the oestrogen receptor genes and APOE*ε4 allele with cognitive impairment using a case-control design.

SETTING

Participants were prospectively recruited from the neurology departments of several Basque Country hospitals.

PARTICIPANTS

This study comprised 816 Caucasian participants who were aged 50 years and older: 204 MCIa, 350 sporadic patients with AD and 262 healthy controls.

PRIMARY AND SECONDARY OUTCOME MEASURES

Clinical criteria and neuropsychological tests were used to establish the diagnostic groups (MCIa, AD and healthy controls). A dichotomous variable was used for each allele and genotype and the association with MCIa and AD was established using Logistic Regression Models.

RESULTS

Neither alleles nor genotypes of SNPs rs9340799, rs2234693, rs2228480 and rs4986938 of oestrogen receptor genes (ESR1 and ESR2) are independently associated with the risk of MCIa or AD. However, the genetic profile created with the combination of the less represented alleles of these SNPs (expressed as XPAA) was associated with an increased risk for MCIa (OR=3.30, 95% CI 1.28 to 8.54, p=0.014) and AD (OR=5.16, 95% CI 2.19 to 12.14, p<0.001) in women APOE*ε4 allele carriers.

CONCLUSIONS

The less represented alleles of SNPs studied are associated with MCIa and AD in APOE*E4 carriers. In particular, the genetic profile created with the less represented alleles of ESR1 and ESR2 SNPs are associated with an increased risk for MCIa and AD in women APOEε4 allele carriers.

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

Aims

The aim of this study was to evaluate the combined contribution of 8 polymorphisms to the risk of Alzheimer's disease (AD).

Methods

Through a comprehensive literature search for genetic variants involved in the AD association study, we harvested a total of 6 genes (8 polymorphisms) for the current meta-analyses. These genes consisted of A2M (5bp I/D and V1000I), ABCA2 (rs908832), CHAT (1882G >A, 2384G >A), COMT (Val158Met), HTR6 (267C >T) and LPL (Ser447Ter).

Results

A total of 33 studies among 9,453 cases and 10,833 controls were retrieved for the meta-analyses of 8 genetic variants. It was showed that A2M V1000I (odd ratio (OR) = 1.26, 95% confidence interval (CI) = 1.07–1.49, P = 0.007), rs908832 allele of ABCA2 (OR = 1.55, 95% CI = 1.12–2.16, P = 0.009), 2384G >A of CHAT (OR = 1.22, 95% CI = 1.00–1.49, P = 0.05) and Ser447Ter of LPL in the Northern-American population (OR = 0.56, 95% CI = 0.35–0.91, P = 0.02) were significantly associated with the risk of AD. No association was found between the rest of the 5 polymorphisms and the risk of AD.

Conclusion

Our results showed that A2M V1000I polymorphism in German, Korean, Chinese, Spanish, Italian and Polish populations, rs90883 of ABCA2 gene in French, American, Swiss, Greek and Japanese populations, 2384G >A of CHAT gene in British and Korean populations and LPL Ser447Ter in the Northern-American population were associated with the risk of AD.

Association of methylenetetrahydrofolate reductase polymorphisms with susceptibility to Alzheimer's disease

BACKGROUND

Genetic risk factors play an important role in the pathogenesis of Alzheimer's disease (AD). In this case-control study, we examined the C677T and A1298C polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene and their correlation with this pathology.

OBJECTIVE

To verify the association between MTHFR C677T and A1298C polymorphisms and Alzheimer's disease.

METHOD

This work was conducted as a case-control study. Cases consisted of thirty-eight patients and 100 individuals without dementia constituted the control group. Genotyping of MTHFR polymorphisms was performed on patients and controls.

RESULT

Genetic analyses did not indicate a significant association between the MTHFR C677T mutation and AD (C/T: 63.15% versus 39%, p=0.087). However, the genotype prevalence of the missense variant MTHFR A1298C was significantly different between patients and controls (A/C: 55% versus 7%, p<10(-3)). Our data suggest an association between the MTHFR A1298C mutation and AD; however, the MTHFR C677T mutation did not contribute to susceptibility for AD.

CONCLUSION

The MTHFR A1298C polymorphism is a possible risk factor for Alzheimer's disease.

The MTHFR 677T allele may influence the severity and biochemical risk factors of Alzheimer's disease in an Egyptian population

OBJECTIVE

We evaluated whether the methylenetetrahydrofolate reductase (MTHFR) 677C>T marker influences the risk and severity of Alzheimer's disease (AD) and whether AD is associated with homocysteine, vitamin B12, and cholesterol levels in Egypt.

METHODS

Forty-three Alzheimer's cases and 32 non-AD controls were genotyped for the 677C>T polymorphism. Clinical characteristics and levels of homocysteine, vitamin B12, and cholesterol were assessed.

RESULTS

No significant differences in the frequencies of the MTHFR alleles or genotypes between AD cases and controls (P = 0.14) were identified. The 677T mutant allele was significantly overrepresented in AD cases compared to controls (OR = 2.22; P = 0.03). The 677T/T frequency was three times higher in AD patients than in controls, which could increase plasma homocysteine levels. Severe cases of AD were the most frequent in patients with the T/T genotype (11.6%). The effect of the MTHFR polymorphism on the risk of AD may be independent of homocysteine, vitamin B12, or even cholesterol levels.

CONCLUSIONS

The MTHFR 677C>T polymorphism--especially the presence of one copy of the T allele--appears to confer a potential risk for the development of AD. The T/T genotype may contribute to hypercysteinemia as a sensitive marker.

Common folate gene variant, MTHFR C677T, is associated with brain structure in two independent cohorts of people with mild cognitive impairment

A commonly carried C677T polymorphism in a folate-related gene, MTHFR, is associated with higher plasma homocysteine, a well-known mediator of neuronal damage and brain atrophy.

As homocysteine promotes brain atrophy, we set out to discover whether people carrying the C677T MTHFR polymorphism which increases homocysteine, might also show systematic differences in brain structure.

Using tensor-based morphometry, we tested this association in 359 elderly Caucasian subjects with mild cognitive impairment (MCI) (mean age: 75 ± 7.1 years) scanned with brain MRI and genotyped as part of Alzheimer's Disease Neuroimaging Initiative. We carried out a replication study in an independent, non-overlapping sample of 51 elderly Caucasian subjects with MCI (mean age: 76 ± 5.5 years), scanned with brain MRI and genotyped for MTHFR, as part of the Cardiovascular Health Study. At each voxel in the brain, we tested to see where regional volume differences were associated with carrying one or more MTHFR ‘T’ alleles.

In ADNI subjects, carriers of the MTHFR risk allele had detectable brain volume deficits, in the white matter, of up to 2–8% per risk T allele locally at baseline and showed accelerated brain atrophy of 0.5–1.5% per T allele at 1 year follow-up, after adjusting for age and sex. We replicated these brain volume deficits of up to 5–12% per MTHFR T allele in the independent cohort of CHS subjects.

As expected, the associations weakened after controlling for homocysteine levels, which the risk gene affects. The MTHFR risk variant may thus promote brain atrophy by elevating homocysteine levels.

This study aims to investigate the spatially detailed effects of this MTHFR polymorphism on brain structure in 3D, pointing to a causal pathway that may promote homocysteine-mediated brain atrophy in elderly people with MCI.

Association between interleukin-1α C(-889)T polymorphism and Alzheimer's disease: a meta-analysis including 12,817 subjects

Epidemiological studies have evaluated the association between interleukin-1 (IL-1)α C(-889)T polymorphism and Alzheimer's disease (AD), but the results remain inconclusive. This meta-analysis was, therefore, designed to clarify these controversies. Systematic searches of electronic databases Embase, PubMed, and Web of Science as well as hand searching of the references of identified articles and the meeting abstracts were performed. Statistical analyses were performed using software Review Manager (Version 5.1.2) and Stata (Version 11.0). The pooled odds ratios (ORs) with 95 % confidence intervals (95 % CIs) were calculated. A total of 28 publications including 29 studies were involved. There was a significant association between IL-1α C(-889)T polymorphism and AD (for T allele vs. C allele: OR = 1.14, 95 % CI = 1.07-1.21; for T/T vs. C/C: OR = 1.39, 95 % CI = 1.18-1.63; for dominant model: OR = 1.13, 95 % CI = 1.04-1.22; and for recessive model: OR = 1.39, 95 % CI = 1.20-1.60). Significant association was found for Asians, Caucasians, and early-onset Alzheimer's disease (EOAD) but for late-onset Alzheimer's disease (LOAD). This meta-analysis indicates that there is a significant association between IL-1α C(-889)T polymorphism and AD as well as EOAD.

Progression from amnesic mild cognitive impairment to Alzheimer's disease: ESR1 and ESR2 polymorphisms and APOE gene

BACKGROUND

Many genes have been studied to determine how they might be involved in Alzheimer's disease (AD). Estrogens have a protective effect in the central nervous system. The mechanisms of action of estrogens are mediated by two estrogen receptors (ERs), ERα and ERβ. Thus, these genes could also play a role in the progression of amnesic mild cognitive impairment (MCIa) to AD. The aim of this study was to examine the role of ER single nucleotide polymorphisms (SNPs) as a risk factor for MCIa, as well as the interaction with apolipoprotein E (APOE) ε4 in the progression to AD.

METHODS

79 MCIa patients and 138 healthy controls were analyzed. SNPs were genotyped via restriction fragment length polymorphisms and real-time PCR, RT-PCR or RT-PCR (TaqMan) assays.

RESULTS

There is a lack of association between MCIa patients who converted to AD and ER SNPs. APOE ε4 allele is an independent risk factor of MCIa (OR=1.86; 95% CI=1.02-3.38, p=0.042) with a high prevalence in converted subjects. APOE ε4 is able to predict the progression from MCIa patients to AD (OR=2.55; 95% CI=1.20-5.42, p=0.015).

CONCLUSIONS

The presence of the APOE ε4 allele, and not the alleles of ER SNPs, is a risk factor for MCIa. Furthermore, APOE genotype seems to predict the conversion from MCIa to AD.

Presenilin-2 polymorphisms and risk of sporadic AD: evidence from a meta-analysis

Association studies of presenilin-2 (PSEN2) polymorphisms and sporadic Alzheimer's disease (AD) have yielded inconsistent results, possibly because single studies often lack sufficient statistical power. In this study, we performed a meta-analysis to evaluate the association of the two most extensively studied PSEN2 polymorphisms, rs8383 and 5'indel, with the risk of sporadic AD. We systematically reviewed relevant studies retrieved by Medline, Pubmed, Embase, AlzGene, and CNKI. Data were analyzed using the Stata (v11.0) software package. The fixed effects model or random-effects model were applied depending on between-study heterogeneity. Publication bias was evaluated using Egger's test and Begg's funnel plots. Overall, the meta-analysis included 6 case-control studies for each polymorphism with 2186 confirmed AD cases and 2507 healthy controls in total. Analysis suggested a significant association between SNP rs8383 polymorphism and AD risk with no evidence of between-study heterogeneity or publication bias. In contrast, we found no evidence for an association between the 5'indel polymorphism and AD risk. Further stratified analyses by apolipoprotein ε4 status or ethnicity also failed to reveal a statistically significant association between the 5'indel polymorphism of PSEN2 and AD risk. Our analysis supports the hypothesis that the PSEN2 rs8383 polymorphism is associated with an enlarged risk of sporadic AD. However, larger scale association studies are necessary to further validate the association of PSEN2 polymorphisms with sporadic AD risk and to define potential gene-gene interactions.

Meta-analysis of the association between the interleukin-1A -889C/T polymorphism and Alzheimer's disease

No clear consensus has been reached on the Interleukin-1A (IL-1A) -889C/T polymorphism and Alzheimer's disease (AD) risk. In this meta-analysis, 27 case-control studies were assessed to evaluate the possible association. Overall, positive associations of the IL-1A -889C/T polymorphism with AD risk were found in allele comparison T vs. C (OR = 1.09, 95% CI = 1.01-1.18), recessive model TT vs. CT + CC (OR = 1.21, 95% CI = 1.01-1.45), and homozygote comparison (TT vs. CC; OR = 1.32, 95% CI = 1.04-1.67). In subgroup analysis stratified by ethnicity, significant associations were demonstrated in Caucasians but not in Asians. In subgroup analysis according to the age of onset, the data showed a significant association in patients with late-onset AD in Caucasians but not in early-onset AD. In conclusion, this meta-analysis supports the idea that IL-1A -889C/T polymorphism is capable of causing AD and LOAD susceptibility in Caucasians but not in Asians.

Genotype–Environment Interactions: Cognitive Aging and Social Factors

The possibility of genotype–environment interaction for memory performance and change was examined in 150 monozygotic (MZ) twin pairs from the Swedish Adoption Twin Study of Aging (SATSA). We used an MZ twin pair difference approach to examine the possibility that genotype was associated with intrapair variability and thus suggestive of genotype–nonshared environment interactions. Multiple ‘variability genes’ were found for longitudinal change in a semantic memory task including candidates coding for apolipoprotein E (APOE) and estrogen receptor alpha (ESR1) as well as serotonin candidates (HTR2Aand5HTT). One candidate also related to variability in change in episodic memory (5HTT). Of the significant associations observed, generally results indicated that MZ pairs who carry putative risk alleles were less variable than noncarriers, suggesting that noncarriers may be more sensitive to environmental contexts. We sought to ‘contextualize’ the possible nonshared environmental influences for found gene–environment (G × E) effects by considering intrapair differences in measured social and stress factors, including social support, life events and depressive symptoms. Results suggested that nonshared environmental influences associated with depressive symptoms may moderate the G × E relationship observed forESR1andAPOEand longitudinal semantic memory change whereby noncarriers of putative risk alleles may be relatively more sensitive to depressionevoking environmental contexts than carriers of the risk allele. Thus, the contexts that facilitate or reduce depressive symptoms may affect semantic memory resiliency dependent on genotype. Further work ought to consider larger sample sizes as well as consider additional social and contextual factors.

Interleukin-1A -889C/T polymorphism and risk of Alzheimer's disease: a meta-analysis based on 32 case-control studies

The Interleukin-1A (IL-1A) -889C/T polymorphism has been reported to be associated with Alzheimer's disease (AD) susceptibility, but the results of these previous studies have been inconsistent. The aim of this study was to explore whether the IL-1A -889C/T polymorphism confers susceptibility to AD. All studies published up to July 2011 on the association between the IL-1A -889C/T polymorphism and AD risk were identified by searching electronic databases PubMed, Embase and Alzgene. The association between the IL-1A -889C/T polymorphism and AD risk was assessed by odds ratios (ORs) together with their 95% confidence intervals (CIs). A total of 32 case-control studies including 7,046 AD cases and 7,534 controls were eventually identified. Overall, positive associations of the IL-1A -889C/T polymorphism with AD risk were found in allele comparison T versus C (OR = 1.019, 95% CI= 1.027-1.198), recessive model TT versus CT + CC (OR = 1.278, 95% CI = 1.073-1.522) and dominant model TT + CT versus CC (OR = 1.102, 95% CI = 1.013-1.200). In subgroup analysis stratified by ethnicity, significant associations were demonstrated in Caucasians but not in Asians. In subgroup analysis according to the age of onset, no significant association was detected. The present meta-analysis suggests that the IL-1A is a candidate gene for AD susceptibility. The IL-1A -889C/T889C/T polymorphism may be a risk factor for AD in Caucasians. Further investigations taking the APOE ε4 status and other confirmed genetic factors and potential gene-gene and gene-environmental interactions into consideration for this polymorphism should be conducted.

Association between the MTHFR gene and Alzheimer's disease: a meta-analysis

BACKGROUND

The association between methylenetetrahydrofolate reductase (MTHFR) gene (rs1801133) 677C/T polymorphism and Alzheimer's disease (AD) is controversial. The objective of the study was to investigate the possible association between MTHFR 677C/T polymorphism and AD.

METHOD

We performed a meta-analysis pooling data from all relevant studies including 3,299 cases and 4,363 controls. We applied a random-effects or fixed-effects model to combine odds ratio (OR) and 95% confidence intervals (95% CI).

RESULTS

This meta-analysis demonstrated that the MTHFR T allele or dominant model for T allele (CT + TT) had an increased risk for AD in combined populations (OR, 95% CI: 1.13, 1.05-1.21; 1.18, 1.07-1.31, respectively), and a significant association was found in allele contrast, recessive, and dominant model in Asian populations, but not in Caucasian populations.

CONCLUSION

The MTHFR C677T polymorphism is associated with AD in Asian populations, but not in Caucasians.

Genetic polymorphism in exon 2 of cathepsin D is not associated with vascular dementia

BACKGROUND

Cathepsin D, the most abundant lysosomal and endosomal aspartyl protease, shows beta and gamma secretase activity in vitro by cleaving the amyloid precursor protein (APP) into amyloid beta protein (Aβ). Polymorphism at position 224, C224T, on exon 2 of cathepsin D gene (CTSD) has been associated with an increased risk for Alzheimer's disease (AD) by some investigators, but there have been contrary findings by others. However, an association between CTSD polymorphism and vascular dementia (VaD) has not been reported thus far.

OBJECTIVE

To investigate whether a polymorphism at CTSD C224T is associated with VaD in the Korean population.

METHODS

We compared the genotype and allele frequencies at this polymorphism site in clinically assessed 162 VaD patients with those in 197 healthy Koreans.

RESULTS AND CONCLUSION

The major genotype frequency at CTSD C224T in normal controls was higher in the Asian population than in various European populations. Our study does not show a significant difference in genotype (P=0.3071) and allele (P=0.2291) frequencies of CTSD C224T between VaD and normal controls. This was the first genetic association study of CTSD in a VaD population.

A review of estrogen receptor alpha gene (ESR1) polymorphisms, mood, and cognition

OBJECTIVE

There are significant individual differences in the extent to which mood and cognition change as a function of reproductive stage, menstrual phase, postpartum, and hormone therapy use. This review explores the extent to which variations or polymorphisms in the estrogen receptor alpha gene (ESR1) predict cognitive and mood outcomes.

METHODS

A literature search was conducted from 1995 to November 2009 through PubMed, Embase, and PsychINFO. Twenty-five manuscripts that summarize investigations of ESR1 in mental health were reviewed.

RESULTS

Among studies investigating ESR1 in relation to cognition, 11 of 14 case-control studies reported an association between ESR1 polymorphisms and risk for developing dementia. Three of four prospective cohort studies reported an association between ESR1 polymorphisms and significant cognitive decline. There are inconsistencies between case-control and cohort studies regarding whether specific ESR1 alleles increase or decrease the risk for cognitive dysfunction. The relationships between ESR1 and cognitive impairment tend to be specific to or driven by women and restricted to risk for Alzheimer disease rather than other dementia causes. Three of five studies examining ESR1 polymorphisms in relation to anxiety or depressive symptoms found significant associations. Significant associations have also been reported between ESR1 polymorphisms and childhood-onset mood disorder and premenstrual dysphoric disorder.

CONCLUSIONS

A strong relationship between ESR1 variants and cognitive outcomes is evident, and preliminary evidence suggests a role of the ESR1 gene in certain mood outcomes. Insights into the discordant results will come from future studies that include haplotype analyses, analyses within specific ethnic/racial populations, and sex-stratified analyses.

Association between NOS3 gene G894T polymorphism and late-onset Alzheimer disease in a sample from Iran

Alzheimer disease (AD) is the most common age-associated neurodegenerative disease caused by complicated interactions between genetic and environmental factors. The presence of the apolipoprotein epsilon4 allele, the only confirmed genetic risk factor for late-onset AD (LOAD), is neither sufficient nor necessary to explain all occurrences of the disease. Aberrant expression of the endothelial nitric oxide synthase (NOS3) gene has been demonstrated in degenerating neurons and glial cells in brains with AD. Molecular epidemiologic studies have presented contradictory results concerning a potential role of NOS3 gene G894T polymorphism in AD. To define a possible association of this polymorphism with LOAD in an Iranian population, we conducted a case-control study including a clinically well-defined group of 100 LOAD patients and 100 age-matched controls. G894T polymorphism in NOS3 gene was determined by polymerase chain reaction-restriction fragment length polymorphisms assay. Chi-square analysis showed a significantly increased number of individuals with the G/G genotype in AD patients compared with controls (P<0.05). These results demonstrate an association between G894T polymorphism and LOAD in an Iranian sample and the G/G genotype seems to have some effects in the development of AD either alone or through interaction with other risk factors.

Meta-analysis of the methylenetetrahydrofolate reductase C677T polymorphism and susceptibility to Alzheimer's disease

No clear consensus has been reached at the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and Alzheimer's disease (AD) risk. Thus in this meta-analysis, a total of 19 case-control studies was assessed to evaluate the possible association. The data demonstrated that the frequency of T677 allele (T vs. C) was significantly associated with susceptibility to AD in all subjects (OR=1.15, 95% CI=1.06-1.26) and in East Asians (OR=1.22, 95% CI=1.08-1.39). There was statistical difference between AD patients and the controls under recessive genetic mode (CT+TT vs. CC) and homozygote comparison (TT vs. CC) in all subjects and in East Asians as well. Despite a small effect of the polymorphism on late-onset AD (LOAD) risk, MTHFR C677T polymorphism was not a major risk factor for LOAD in East Asians and Caucasians. A subgroup analysis in the subjects without APOE epsilon4 alleles showed T677 allele significantly increased risk of AD in all subjects (OR=1.21, 95% CI: 1.04-1.42) and in East Asians (OR=1.28, 95% CI: 1.06-1.55). However, no association was found in Caucasians. In conclusion, this meta-analysis supports that MTHFR C677T polymorphism is capable of causing AD susceptibility in East Asians, not in Caucasians.

The cathepsin D (224C/T) polymorphism confers an increased risk to develop Alzheimer's disease in men

The lysosomal protease cathepsin D is likely involved in beta-amyloidogenesis in Alzheimer's disease (AD). There is evidence for a single nucleotide polymorphism (rs17571) of the cathepsin D gene to be associated with increased AD risk. However, little is known about gender-specific differences. Therefore, we performed a genetic association study focusing on gender-specific differences in 434 participants (219 AD and 215 controls). Screening of the rs17571 shows a significantly higher proportion of T-allele carriers among male Alzheimer patients (28.5%) when compared with male controls (13.8%, p = .013, p(corr) = .039). The odds ratio was 2.48 (95% confidence interval: 1.14-5.58). There was no significant difference in the T-allele distribution in women. Including APOE4 status and age did not have an additional effect on the morbidity risk. Thus, our results support the idea that rs17571 confers an increased risk for AD in men but not in women. Further investigation should substantiate the role of gender for AD risk of rs17571.

Pharmacology of epigenetics in brain disorders

Epigenetics is a rapidly growing field and holds great promise for a range of human diseases, including brain disorders such as Rett syndrome, anxiety and depressive disorders, schizophrenia, Alzheimer disease and Huntington disease. This review is concerned with the pharmacology of epigenetics to treat disorders of the epigenome whether induced developmentally or manifested/acquired later in life. In particular, we will focus on brain disorders and their treatment by drugs that modify the epigenome. While the use of DNA methyl transferase inhibitors and histone deacetylase inhibitors in in vitro and in vivo models have demonstrated improvements in disease-related deficits, clinical trials in humans have been less promising. We will address recent advances in our understanding of the complexity of the epigenome with its many molecular players, and discuss evidence for a compromised epigenome in the context of an ageing or diseased brain. We will also draw on examples of species differences that may exist between humans and model systems, emphasizing the need for more robust pre-clinical testing. Finally, we will discuss fundamental issues to be considered in study design when targeting the epigenome.

Cathepsin D gene and the risk of Alzheimer's disease: a population-based study and meta-analysis

Cathepsin D (CTSD) is a gene involved in amyloid precursor protein processing and is considered a candidate for Alzheimer's disease (AD). The aim of the current study was to examine if variation in CTSD increases the risk of AD. We performed a candidate-gene analysis in a population-based cohort study (N=7983), and estimated the effect of CTSD on the risk of AD. Additionally, a large meta-analysis was performed incorporating our data and previously published data. The T-allele of CTSD rs17571 was associated with an increased risk of AD (p-value 0.007) in the Rotterdam Study. This association was predominantly found in APOE ε4 noncarriers. A meta-analysis of previously published data showed a significantly increased risk of AD in carriers of the T-allele of rs17571 (OR 1.22, 95% CI 1.03-1.44), irrespective of APOE ε4 carrier status. This study adds to the evidence that CTSD increases the risk of AD, although the effect size is moderate.

Mice deficient in dihydrolipoyl succinyl transferase show increased vulnerability to mitochondrial toxins

The activity of a key mitochondrial tricarboxylic acid cycle enzyme, alpha-ketoglutarate dehydrogenase complex (KGDHC), declines in many neurodegenerative diseases. KGDHC consists of three subunits. The dihydrolipoyl succinyl transferase (DLST) component is unique to KGDHC. DLST(+/-) mice showed reduced mRNA and protein levels and decreased brain mitochondrial KGDHC activity. Neurotoxic effects of mitochondrial toxins were exacerbated in DLST(+/-) mice. MPTP produced a significantly greater reduction of striatal dopamine and tyrosine hydroxylase-positive neurons in the substantia nigra pars compacta of DLST(+/-) mice. DLST deficiency enhanced the severity of lipid peroxidation in the substantia nigra after MPTP treatment. Striatal lesions induced by either malonate or 3-nitropropionic acid (3-NP) were significantly larger in DLST(+/-) mice than in wildtype controls. DLST deficiency enhanced the 3-NP inhibition of mitochondria enzymes, and 3-NP induced protein and DNA oxidations. These observations support the hypothesis that reductions in KGDHC may impair the adaptability of the brain and contribute to the pathogenesis of neurodegenerative diseases.

Neuroglobin and Alzheimer's dementia: genetic association and gene expression changes

We previously reported strong genetic linkage on chromosome 14q to Alzheimer's disease (AD) using the presence of co-morbid hallucinations as a covariate. Those results suggested the presence of a gene increasing the risk for a genetically homogeneous form of AD characterized by the absence of comorbid hallucinations. Here we report our follow up of that study through the analysis of single nucleotide polymorphisms (SNPs) in five functional candidate genes. This work provides significant evidence of association for the gene coding for neuroglobin (NGB), a nervous system globin known to protect cells against amyloid toxicity and to attenuate the AD phenotype of transgenic mice. On further experiments we found that NGB expression is reduced with increasing age and lower in women consistent with their increased risk. NGB expression is up-regulated in the temporal lobe of AD patients consistent with a response to the disease process, as reported for NGB and hypoxia. We speculate that a compromised response due to DNA variation might increase the risk for AD. Our and others' data strongly support the involvement of NGB in AD.

Association of amyloid precursor protein-binding protein, family B, member 1 with nicotine dependence in African and European American smokers

Although epidemiological studies reveal that cigarette smoking is inversely associated with Alzheimer's disease (AD) and Parkinson's disease (PD), the underlying mechanism remains largely unknown. Considering the facts that amyloid precursor protein-binding protein, family B, member 1 (APBB1) is mapped to a suggestive linkage region on chromosome 11 for nicotine dependence (ND), and has been implicated in the pathogenesis of AD and PD, it represents a plausible candidate for genetic study of ND. Five single nucleotide polymorphisms (SNPs) within APBB1 were genotyped in a sample consisting of 2,037 participants of either African-American (AA) or European-American (EA) origin, and examined their associations with ND assessed by three commonly used measures: Smoking Quantity (SQ), the Heaviness of Smoking Index (HSI), and the Fagerström Test for ND (FTND). Individual SNP-based association analysis showed that all five SNPs are associated with at least one ND measure in one of the three samples; however, only the association of SNP rs4758416 with SQ and HSI remained significant after correction for multiple testing in the pooled sample. Haplotype analysis demonstrated three major haplotypes significantly associated with ND after Bonferroni correction. Formed by rs4758416-rs10839562-rs1079199, haplotype C-C-T showed positive association with FTND in the AA and pooled samples, and conversely, haplotype G-C-T showed negative association with SQ and HSI in AA and EA samples. Another haplotype, C-T-G, formed by rs10839562-rs1079199-rs8164, was significantly associated with HSI in the EA sample. Based on these findings, we conclude that APBB1 represents an important candidate gene in the genetic study on ND and neurodegenerative diseases and warrants further investigation in future.