Variation in the DCP1 gene, encoding the angiotensin converting enzyme ACE, is not associated with increased susceptibility to Alzheimer's disease

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.

Genetic and environmental factors in vascular dementia: an update of blood brain barrier dysfunction

Vascular dementia (VaD) describes a combination of both cognitive and behavioural manifestations associated with variable brain lesions of vascular origin. While vascular risk factors have been implicated in VaD, the relationship is most evident when the factors are considered together and not individually. This review will examine the significance of the integrity of blood brain barrier (BBB) tight junction (TJ) proteins - occludin and claudins in the pathophysiology of VaD. Specifically, some of the genetic contributors to VaD, namely those responsible for the integrity of the BBB, will be reviewed in detail. Moreover, environmental factors will be considered in conjunction with these genes to examine how the interaction of environmental and genetic factors contributes to one's susceptibility to VaD.

Angiotensin-converting enzyme gene insertion-deletion polymorphism is a risk marker for Alzheimer's disease in a Chinese population: a meta-analysis of case-control studies

It has long been known that the polymorphisms of angiotensin-converting enzyme gene (ACE) are associated to increase risk of Alzheimer's disease (AD) in Chinese population. However, consistent results were not obtained among studies. This study is aimed to clarify the association between ACE insertion (I)/deletion (D) polymorphism (rs1799752) and AD. Literatures were searched from PubMed, Embase, Cochrane Library, CNKI, Wanfang and VIP databases without language restrictions. Eleven separate studies were suitable for the inclusion criterion. The selected studies contained 2,763 Chinese participants, including 1,383 in AD group and 1,380 controls. Pooled odds ratios (ORs) were calculated to assess the association between ACE I/D polymorphism and AD. Our case-control data indicated that ACE insertion is a risk allele in all genetic models: additive model (I vs. D: OR = 1.32, 95 % CI 1.07-1.62, P = 0.008), dominant model (II + ID vs. DD: OR = 1.61, 95 % CI 1.08-2.41, P = 0.02) and recessive model (II vs. ID + DD: OR = 1.39, 95 % CI 1.07-1.81, P = 0.01). Heterogeneity between studies was significant (P < 0.10) but not in stratification defined by the selection of controls (P > 0.10). After stratification according to the selection of controls, the carrier of ACE I allele remained a high risk for AD in population-based samples subgroup (I vs. D: P = 0.008, OR = 1.32, 95 % CI 1.07-1.61, P(heterogeneity) = 0.47, I (2) = 0 %). Our study provided solid evidence suggesting that ACE gene I/D polymorphism is a genetic risk factor for AD in Chinese population.

Angiotensin-converting enzyme insertion/deletion polymorphism is not a major determining factor in the development of sporadic Alzheimer disease: evidence from an updated meta-analysis

Angiotensin-converting enzyme gene (ACE) insertion/deletion (I/D) polymorphism have long been linked to sporadic Alzheimer disease (SAD), but the established data remained controversial. To clarify this inconsistency, a comprehensive meta-analysis was conducted. Through searching of Pubmed, Embase, Alzgene, China National Knowledge Infrastructure (CNKI) and manually searching relevant references, 53 independent studies from 48 articles were included, involving a total of 8153 cases and 14932 controls. The strength of association was assessed by using odds ratios (ORs) with 95% confidence intervals (CIs). Further stratified analyses and heterogeneity analyses were tested, as was publication bias. Overall, significant associations were revealed between I/D polymorphism and SAD risk using allelic comparison (OR = 1.09, 95%CI = 1.01–1.17, p = 0.030), homozygote comparison (OR = 1.17, 95%CI = 1.01–1.34, p = 0.030) and the dominant model (OR = 1.16, 95%CI = 1.04–1.29, p = 0.008), but they were not sufficiently robust to withstand the false-positive report probability (FPRP) analyses. Otherwise, in subgroup analyses restricted to the high quality studies, the large sample size studies and studies with population-based controls, no significant association was observed in any genetic models. In summary, the current meta-analysis suggested that the ACE I/D polymorphism is unlikely to be a major determining factor in the development of SAD.

ACE I/D polymorphism in Alzheimer’s disease

Angiotensin-converting enzyme (ACE) has been reported to show altered activity in patients with neurological diseases. The recent studies found that a 287 bp insertion/deletion (I/D) polymorphism of the ACE gene may be associated with susceptibility to Alzheimer’s disease (AD) but the results have been heterogenous between studies in Europe. In the present study we examined for the first time the association of ACE I/D polymorphism along with APOE genotype in 70 sporadic AD and 126 control subjects in Slovak Caucasians (Central Europe). An increased risk for AD was observed in subjects with at least one APOE*E4 allele (OR=3.99, 95% CI=1.97–8.08). No significant differences for the genotype distribution or the allele frequency were revealed comparing controls and patients for ACE gene. Gene-gene interaction analysis showed increase of the risk to develop AD in subjects carrying both the ACE DD genotype and the APOE*E4 allele (OR=10.32, 95% C.I. 2.67–39.81).

Pharmacogenomics in Alzheimer's disease

Pharmacological treatment in Alzheimer's disease (AD) accounts for 10-20% of direct costs, and fewer than 20% of AD patients are moderate responders to conventional drugs (donepezil, rivastigmine, galantamine, memantine), with doubtful cost-effectiveness. Both AD pathogenesis and drug metabolism are genetically regulated complex traits in which hundreds of genes cooperatively participate. Structural genomics studies demonstrated that more than 200 genes might be involved in AD pathogenesis regulating dysfunctional genetic networks leading to premature neuronal death. The AD population exhibits a higher genetic variation rate than the control population, with absolute and relative genetic variations of 40-60% and 0.85-1.89%, respectively. AD patients also differ in their genomic architecture from patients with other forms of dementia. Functional genomics studies in AD revealed that age of onset, brain atrophy, cerebrovascular hemodynamics, brain bioelectrical activity, cognitive decline, apoptosis, immune function, lipid metabolism dyshomeostasis, and amyloid deposition are associated with AD-related genes. Pioneering pharmacogenomics studies also demonstrated that the therapeutic response in AD is genotype-specific, with apolipoprotein E (APOE) 4/4 carriers the worst responders to conventional treatments. About 10-20% of Caucasians are carriers of defective cytochrome P450 (CYP) 2D6 polymorphic variants that alter the metabolism and effects of AD drugs and many psychotropic agents currently administered to patients with dementia. There is a moderate accumulation of AD-related genetic variants of risk in CYP2D6 poor metabolizers (PMs) and ultrarapid metabolizers (UMs), who are the worst responders to conventional drugs. The association of the APOE-4 allele with specific genetic variants of other genes (e.g., CYP2D6, angiotensin-converting enzyme [ACE]) negatively modulates the therapeutic response to multifactorial treatments affecting cognition, mood, and behavior. Pharmacogenetic and pharmacogenomic factors may account for 60-90% of drug variability in drug disposition and pharmacodynamics. The incorporation of pharmacogenetic/pharmacogenomic protocols to AD research and clinical practice can foster therapeutics optimization by helping to develop cost-effective pharmaceuticals and improving drug efficacy and safety.

The insertion polymorphism in angiotensin-converting enzyme gene associated with the APOE epsilon 4 allele increases the risk of late-onset Alzheimer disease

Several studies have shown that a common insertion (I)/deletion (D) polymorphism of angiotensin-converting enzyme (ACE) gene may confer an increased risk of late-onset Alzheimer disease (LOAD). However, the result has not been replicated by all studies. In order to clarify the role of the polymorphism for the occurrence of LOAD in Chinese and the possibility of a synergistic effect with the apolipoprotein E allele 4 on the risk of Alzheimer disease, we examined the ACE and APOE genotypes in a Chinese sample consisting of 104 sporadic LOAD patients and 128 healthy controls. An obvious difference of allelic and genotypic distributions of ACE I/D polymorphism between cases and controls was observed (chi2 = 6.61, df = 2, p = 0.037 by genotype; chi2 = 4.67, df = 1, p = 0.031 by allele). And ACE I allele carriers showed an increased risk for LOAD developing (chi2 = 6.59, df = 1, p =0.01, OR = 2.91, 95% CI 1.25-6.77). After stratifying by APOE epsilon 4 status, the increased LOAD risks associated with I allele carriers only in the APOE epsilon 4 noncarriers was seen (chi2 = 4.12, df = 1, p = 0.042). Logistic regression analysis of total subjects demonstrated a more than sevenfold increase in the risk of developing LOAD in subjects carrying both the ACE I allele and the APOE epsilon 4 (OR = 7.39, 95% CI 2.50-21.89, p < 0.001). Our data revealed that ACE I/D polymorphism is considered to be an additional risk factor, which has strong synergistic interaction with APOE epsilon 4 on the risk of LOAD.

A Study of Potential Interactive Genetic Factors in Huntington’s Disease

AIM

To assess the role of genetic factors, other than the CAG repeat length, on the development of Huntington's disease (HD) in an isolated Caucasian population in the south-west of Western Australia.

METHODS

114 patients with symptomatic HD according to the Unified HD Rating Scale research criteria were examined along with 51 control patients. The length of the CAG repeat sequence in the IT15 gene and the adjacent CCG and Delta2642 polymorphisms were determined by polymerase chain reaction along with common genotypes of the angiotensin-converting enzyme (ACE) and apolipoprotein E (APOE) genes.

RESULTS

The CAG expansion was associated with age of onset and the development of neurological dysfunction. We found no effect of the expanded CCG allele on age of onset, neurological dysfunction or the size of the CAG expansion. We observed a twofold increase in the Delta2642 polymorphism and the risk of developing symptomatic HD which was not significant (OR 2.06; 95% CI 0.60-7.07). The presence of an APOE epsilon4 allele was associated with an increased risk of HD which was not significant either (OR 1.04-1.73; 95% CI 0.10-10.68). ACE genotypes showed no association with risk factors for the disease.

CONCLUSION

In our study of a geographically isolated Caucasian HD population in the south-west of Western Australia we have not observed that the expanded CCG allele, the Delta2642 polymorphism, the APOE epsilon4 allele and ACE genotypes are associated with an increased risk for the development of symptomatic HD.

Association between angiotensin-converting enzyme gene polymorphism and Alzheimer's disease in a Chinese population

Angiotensin-converting enzyme has shown altered activity in patients with neurological diseases. An insertion/deletion (I/D) polymorphism of the DCP1 gene encoding angiotensin-converting enzyme has been reported to be associated with the risk for Alzheimer's disease (AD), but ambiguous results have also been presented. We conducted a case-control study in a sample composed of 192 sporadic AD patients and 195 age- and sex-matched controls from Chinese Han population in Beijing and Xi'an districts to investigate the possible effect of the polymorphism. Our data revealed no association between the DCP1 polymorphism and AD risk in the total sample. There was no significant difference in the DCP1 allele or genotype frequencies between cases and controls when stratified by gender and APOE epsilon4 status. However, the D allele and D/D genotype were more frequent among AD patients between 66 and 70 years compared with controls (D allele: OR=2.8, 95% CI=1.5-5.2, p=0.001; D/D genotype: OR=5.9, 95% CI=1.7-19.9, p=0.002). Our results provided new proof that the DCP1 D allele was a probable risk factor for late-onset AD. Its role was independent and was limited to the population at a certain age.

Large meta-analysis establishes the ACE insertion-deletion polymorphism as a marker of Alzheimer's disease

Apolipoprotein E epsilon4 (APOE*4) is the only fully established susceptibility allele for Alzheimer's disease. One of the most studied candidates is the insertion (I)/deletion (D) polymorphism (indel) of the gene for angiotensin I-converting enzyme (ACE). This study aimed to clarify its association with Alzheimer's disease. The meta-analysis included 39 samples, comprising 6,037 cases of Alzheimer's disease and 12,099 controls, using mainly primary data. Potential interactions with gender, age, ethnic group, and carrier status of the apolipoprotein E epsilon4 allele were all examined. D homozygotes were at reduced risk of Alzheimer's disease (odds ratio = 0.81, 95% confidence interval: 0.72, 0.90; corrected p = 0.0004); I homozygotes showed no association with Alzheimer's disease, while heterozygotes were at increased risk. Although there were clear differences among the three ethnic groups examined (North Europeans, South Caucasians, and East Asians), in all groups D homozygotes were at reduced risk. These results confirm the association of the angiotensin I-converting enzyme indel with Alzheimer's disease across diverse populations, although this is probably due to linkage disequilibrium with the true risk factor. Further, in North Europeans, both association and Hardy-Weinberg analysis suggested partial heterosis, that is, an increased risk for heterozygotes, due to a hidden interaction with another, as yet unknown, risk factor. This interaction warrants further investigation.

ACE genotype and cognitive decline in an African-Caribbean population

The insertion/deletion (I/D) polymorphism of the angiotensin I converting enzyme (ACE) gene is believed to influence risk of cerebrovascular disease. However, associations with cognitive outcomes remain controversial. As far as we are aware, all studies to date have been carried out in white American or European populations. African-Caribbean populations have high prevalence rates of hypertension, diabetes and cerebrovascular disease but risk factors for cognitive outcomes remain under-researched. In a UK community sample of 148 African-Caribbean people aged 55-75 years, we investigated the association between ACE genotype and cognitive decline over 3 years using a battery of repeated tests. No direct association was found between ACE genotype and decline. However, the association between increased age and cognitive decline was significantly stronger in people with the ACE DD genotype (odds ratio 3.6 per 5-year increase, 95% CI: 1.9-6.7) compared to those with ID/II genotype (odds ratio 0.7, 95% CI 0.4-1.2). This interaction was particularly strong for decline in verbal memory and was not apparently mediated by vascular risk factors measured at baseline.