Using meta-analysis to explain the diversity of results in genetic studies of late-onset Alzheimer's disease and to identify high-risk subgroups

Association of Matrix Metalloproteinase-2 (MMP-2) and MMP-9 Promoter Polymorphisms, Their Serum Levels, and Activities with Coronary Artery Calcification (CAC) in an Iranian Population

The serum levels and activity of matrix metalloproteinases (MMPs) are associated with the risk of coronary artery calcification (CAC). We sought to investigate the association between MMP-2 -1575G>A (rs243866) and MMP-9 -1562 C>T (rs3918242) SNPs with MMP-2 and MMP-9 serum levels and activity in individuals with CAC. One hundred and fifty-five cases with CAC and 155 healthy individuals as control group from West of Iran were included and frequency of genotypes and alleles of rs243866 and rs3918242 in MMP-2 and MMP-9 genes were determined using PCR-RFLP. We also investigated the serum levels of MMP-2 and MMP-9 and their activity using ELISA and gelatin zymography, respectively. Additionally, serum biochemical parameters including FBS (fasting blood sugar), urea, creatinine, cholesterol, triglyceride, HDL (high-density lipoprotein), LDL (low-density lipoprotein), calcium, and phosphorus as well as blood pressure (systolic blood pressure (SBP) and diastolic blood pressure (DBP)) were measured. Our results showed that both serum levels of MMP-2 and MMP-9 (P < 0.001) and their activity (P < 0.001) were higher in individuals with CAC when compared to the control group. Carrying A and T alleles in MMP-2 -1575G>A (rs243866) and MMP-9 -1562 C>T (rs3918242) SNPs, respectively, may predispose the individuals to CAC by acting as the risk factors. Serum levels and activity of MMP-2 and MMP-9 were found to be higher in CAC cases when compared to the healthy controls. Carriers of A allele in rs243866 SNP and T allele in rs3918242 SNP were shown to have higher MMP-2 and MMP-9 serum levels and activity that may result in increased ECM degradation and support the initiation and development of calcification.

Gene Polymorphisms Affecting the Pharmacokinetics and Pharmacodynamics of Donepezil Efficacy

Donepezil (DNP) is the first-line drug used for Alzheimer's disease (AD). However, the therapeutic response rate of patients to DNP varies from 20 to 60%. The main reason for the large differences in the clinical efficacy of DNP therapy is genetic factors, some of which affect pharmacokinetics (PK), while others affect pharmacodynamics (PD). Thus, much emphasis has been placed on the investigation of an association between PK- and PD-related gene polymorphisms and therapeutic response to DNP, but a consistent view does not yet exist. In this review, we summarize recent findings regarding genetic factors influencing the clinical efficacy of DNP, including substantial differences in individual responses as a consequence of polymorphisms in Cytochrome P450 (CYP) 2D6, CY3A4, CY3A5, APOE, ABCA1, ABCB1, ESR1, BCHE, PON-1, CHRNA7, and CHAT. We also discuss possible strategies for the evaluation of the clinical efficacy of DNP, with a specific focus on possible biomarkers of PK/PD parameters, and provide perspectives and limitations within the field, which will also be beneficial for understanding the multiple mechanisms of DNP therapy in AD.

Synergy between the alteration in the N-terminal region of butyrylcholinesterase K variant and apolipoprotein E4 in late-onset Alzheimer's disease

While the life expectancy of the population has increased, Alzheimer’s disease (AD) has emerged as one of the greatest health problems of old age. AD is characterized by neuronal loss and cognitive decline. In the AD brain, there is a decrease in levels of acetylcholinesterase (AChE) and an increase in the levels of the related enzyme butyrylcholinesterase (BChE), that accumulate in plaques and tangles. Apolipoprotein E (ApoE) is a major cholesterol carrier and plays an important role in maintaining lipid homeostasis. APOE-ε4 constitutes the most important known genetic risk factor for late-onset AD. It has been proposed that the BCHE-K allele (Ala539Thr) acts in synergy with the APOE-ε4 allele to promote risk for AD. However, there is insufficient evidence to support a correlation. Most studies focused only on the coding regions of the genes. In this study, we analyzed sequence regions beyond the BCHE coding sequence. We found synergy between APOE-ε4 and SNPs localized in 5′UTR (rs1126680) and in intron 2 (rs55781031) of the BCHE-K allele (rs1803274) in 18% of patients with late-onset AD (n = 55). The results show that the coexistence of the APOE-ε4 allele and 3 SNPs in the BCHE gene is associated with a highly elevated risk of late-onset AD. SNP (rs1126680) in 5′UTR of the BCHE gene is located 32 nucleotides upstream of the 28 amino acid signal peptide. Mass spectrometry analysis of the BChE protein produced by SNP (rs1126680) showed that the mutation caused an in frame N-terminal extension of 41 amino acids of the BChE signal peptide. The resultant variant with a 69 amino acid signal peptide, designated N-BChE, may play a role in development of AD.

Bridging the gap between statistical and biological epistasis in Alzheimer's disease

Alzheimer's disease affects millions of people worldwide and incidence is expected to rise as the population ages, but no effective therapies exist despite decades of research and more than 20 known disease markers. Research has shown that Alzheimer's disease's missing heritability remains extensive with an estimated 25% of phenotypic variance unexplained by known variants. The missing heritability may be explained by missing variants or by epistasis. Researchers often focus on individual loci rather than epistatic interactions, which is likely an oversimplification of the underlying biology since most phenotypes are affected by multiple genes. Focusing research efforts on epistasis will be critical to resolving Alzheimer's disease etiology, and a major key to identifying and properly interpreting key epistatic interactions will be bridging the gap between statistical and biological epistasis. This review covers the current state of epistasis research in Alzheimer's disease and how researchers can bridge the gap between statistical and biological epistasis to help resolve Alzheimer's disease etiology.

Butyrylcholinesterase-knockout reduces brain deposition of fibrillar β-amyloid in an Alzheimer mouse model

In Alzheimer's disease (AD), numerous β-amyloid (Aβ) plaques are associated with butyrylcholinesterase (BChE) activity, the significance of which is unclear. A mouse model, containing five human familial AD genes (5XFAD), also develops Aβ plaques with BChE activity. Knock-out of BChE in this model showed diminished fibrillar Aβ plaque deposition, more so in males than females. This suggests that lack of BChE reduces deposition of fibrillar Aβ in AD and this effect may be influenced by sex.

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.

Apolipoprotein E genotypes associated with Alzheimer disease and concomitant stroke

BACKGROUND

The ɛ4 allele of the apolipoprotein E (APOE) gene is a well-characterized genetic risk factor for Alzheimer disease (AD). The association between stroke and a higher risk for AD has also been reported. Our study sought to determine the relationship between the APOE gene and AD and the comorbid risk of stroke.

METHODS

The subjects of this study consisted of 48 patients with AD and 48 members of a control group. All subjects were genotyped for APOE.

RESULTS

The results clearly show a significant increased risk of AD in carriers of the APOE ε3/ε4 genotype (P = .003, odds ratio [OR] = 4.1) or ε4 allele (P = .001, OR = 4.2). The risk for stroke in AD patients was also increased for carriers of the APOE ε3/ε4 genotype (P = .02, OR = 9.0) and for carriers of the APOE ε4 allele (P = .004, OR = 5.5).

CONCLUSIONS

The present study is the first to establish a relationship between APOE ε4 and concomitant AD and stroke in the Tunisian population.

Response to rivastigmine transdermal patch or memantine plus rivastigmine patch is affected by apolipoprotein E genotype in Alzheimer patients

BACKGROUND/AIMS

The apolipoprotein E (APOE) genotype in response to pharmacological treatments in patients with Alzheimer's disease (AD) remains a matter of controversy. This analysis investigated the effect of the APOE genotype on the clinical response to rivastigmine transdermal patch monotherapy or memantine plus rivastigmine patch in patients with mild to moderate AD.

METHODS

Two hundred and six (n = 206) patients with probable AD and Mini-Mental State Examination (MMSE) scores of 10-20 were randomized to rivastigmine patch monotherapy or memantine plus rivastigmine patch for 24 weeks. Of the 206 patients with probable AD, 146 patients who consented to genetic testing for APOE were included and assessed for this subgroup study.

RESULTS

There were no significant differences on MMSE, NPI, ADAS-cog, ADCS-ADL, CDR-SB, NPI and FAB between rivastigmine patch monotherapy and memantine plus rivastigmine patch according to the APOE genotype. However, patients with moderately severe AD (MMSE ≤15) who were APOE ε4 carriers showed higher responder rates on ADCS-ADL with memantine plus rivastigmine patch compared to rivastigmine patch monotherapy.

CONCLUSION

Moderately severe AD patients with the APOE ε4 allele may respond more favorably to memantine plus rivastigmine patch than ε4 noncarriers.

Butyrylcholinesterase genotype and gender influence Alzheimer's disease phenotype

Retrospective data are presented to support a spectrum of early Alzheimer's disease (AD) along a continuum defined by gender and genotype. The putative neurodegenerative mechanisms driving distinct phenotypes at each end of the spectrum are glial hypoactivity associated with early failure of synaptic cholinergic neurotransmission and glial overactivation associated with loss of neural network connectivity due to accelerated age-related breakdown of myelin. In early AD, male butyrylcholinesterase K-variant carriers with one or two apolipoprotein ɛ4 alleles have prominent medial temporal atrophy, synaptic failure, cognitive decline, and accumulation of aggregated beta-amyloid peptide. Increasing synaptic acetylcholine in damaged but still functional cholinergic synapses improves cognitive symptoms, whereas increasing the ability of glia to support synapses and to clear beta-amyloid peptide might be disease-modifying. Conversely, chronic glial overactivation can also drive degenerative processes and in butyrylcholinesterase K-variant negative females generalized glial overactivation may be the main driver from mild cognitive impairment to AD. Females are more likely than males to have accelerated age-related myelin breakdown, more widespread white matter loss, loss of neural network connectivity, whole brain atrophy, and functional decline. Increasing extracellular acetylcholine levels blocks glial activation, reduces myelin loss and damage to neural network connectivity, and is disease-modifying. Between extremes characterized by gender, genotype, and age, pathophysiology may be mixed and this spectrum may explain much of the heterogeneity of amnestic mild cognitive impairment. Preservation of the functional integrity of the neural network may be an important component of strengthening cognitive reserve and significantly delaying the onset and progression of dementia, particularly in females. Prospective confirmation of these hypotheses is required. Implications for future research and therapeutic opportunities are discussed.

Variation of the butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) genes in coronary artery disease

Butyrylcholinesterase (BChE) and acetylcholinesterase (AchE) are two enzymes of the cholinergic system putatively involved in coronary artery disease (CAD). We investigated two single nucleotide polymorphisms (SNPs) of the genes encoding these enzymes to determine whether some allele or genotype might represent a factor of risk or protection for CAD onset. AChE rs2571598 and BChE rs1803274 (the so-called K-variant) SNPs were investigated in a sample of 199 patients and 199 healthy subjects. No significant results were obtained for BChE, whereas for AChE the A allele was found significantly more frequent in patients than in controls (0.437 vs. 0.332; p=0.002). The crude Odds Ratio (OR) for CAD conferred by carrying the A allele was 1.76 (95% confidence interval [CI] 1.17-2.65). Stratification of the sample by gender revealed that the statistical significance was limited to female, where the crude OR associated with the A allele was 3.26 (95% CI 1.58-6.73). The lipidic pattern was also tested and related to variation of the two SNPs. In this case, an at limits significant result (p=0.03) was obtained for BChE, whose A allele (the K variant) in patients was found associated with higher plasma concentrations of high density lipoprotein-cholesterol.

A pilot study of gene/gene and gene/environment interactions in Alzheimer disease

BACKGROUND

Although some genes associated with increased risk of Alzheimer Disease (AD) have been identified, few data exist related to gene/gene and gene/environment risk of AD. The purpose of this pilot study was to explore gene/gene and gene/environment associations in AD and to obtain data for sample size estimates for larger, more definitive studies of AD.

METHODS

The effect of gene/gene and gene/environment interaction related to late onset Alzheimer Disease (LOAD) was investigated in 153 subjects with LOAD and 302 gender matched controls enrolled in the Personalized Medicine Research Project, a population-based bio-repository. Genetic risk factors examined included APOE, ACE, OLR1,and CYP46 genes, and environmental factors included smoking, total cholesterol, LDL, HDL, triglycerides, C-reactive protein, blood pressure, statin use, and body mass index.

RESULTS

The mean age of the cases was 78.2 years and the mean age of the controls was 87.2 years. APOE4 was significantly associated with LOAD (OR=3.55, 95%CL=1.70, 7.45). Cases were significantly more likely to have ever smoked cigarettes during their life (49.3% versus 38.4%, p=0.03). The highest recorded blood pressure and pulse pressure measurements were significantly higher in the controls than the cases (all P<0.005). Although not statistically significant in this pilot study, the relationship of the following factors was associated in opposite directions with LOAD based on the presence of an APOE4 allele: obesity at the age of 50, ACE, OLR1, and CYP46.

CONCLUSIONS

These pilot data suggest that gene/gene and gene/environment interactions may be important in LOAD, with APOE, a known risk factor for LOAD, affecting the relationship of ACE and OLR1 to LOAD. Replication with a larger sample size and in other racial/ethnic groups is warranted and the allele and risk factor frequencies will assist in choosing an appropriate sample size for a definitive study.

Effect of apolipoprotein E and butyrylcholinesterase genotypes on cognitive response to cholinesterase inhibitor treatment at different stages of Alzheimer's disease

Factors that influence response to drug treatment are of increasing importance. We report an analysis of genetic factors affecting response to cholinesterase inhibitor therapy in 165 subjects with Alzheimer's disease (AD). The presence of apolipoprotein E ε4 (APOE ε4) allele was associated with early and late cognitive response to cholinesterase inhibitor treatment in mild AD (Mini-Mental State Examination (MMSE) ≥21) (P<0.01). In moderate-to-severe AD (MMSE ≤15), presence of the BCHE-K variant was associated with late response to cholinesterase inhibitor treatment (P=0.02). Testing for APOE and BCHE genotypes may be useful in therapeutic decision making.

Suggestive synergy between genetic variants in TF and HFE as risk factors for Alzheimer's disease

Alzheimer's disease (AD) is a complex disease that is likely influenced by many genetic and environmental factors. Citing evidence that iron may play a role in AD pathology, Robson et al. [Robson et al. (2004); J Med Genet 41:261-265] reported that epistatic interaction between rs1049296 (P589S) in the transferrin gene (TF) and rs1800562 (C282Y) in the hemochromatosis gene (HFE) results in significant association with risk for AD. In this study we attempted to replicate their findings in a total of 1,166 cases and 1,404 controls from three European and European American populations. Allele and genotype frequencies were consistent across the three populations. Using synergy factor analysis (SFA) and Logistic Regression analysis we tested each population and the combined sample for interactions between these two SNPs and risk for AD. We observed significant association between bi-carriers of the minor alleles of rs1049296 and rs1800562 in the combined sample using SFA (P = 0.0016, synergy factor = 2.71) and adjusted SFA adjusting for age and presence of the APOE epsilon 4 allele (P = 0.002, OR = 2.4). These results validate those of the previous report and support the hypothesis that iron transport and regulation play a role in AD pathology.

Variability of AChE, BChE, and ChAT genes in the late-onset form of Alzheimer's disease and relationships with response to treatment with Donepezil and Rivastigmine

Several factors are believed to give rise to the late onset sporadic form of Alzheimer's disease (LOAD). We have studied the variation at the genes of three enzymes of the cholinergic system: acetylcholinesterase, butyrylcholinesterase, and choline acetyltransferase. The single nucleotide polymorphisms (SNPs) examined were: AChE rs2571598, BChE rs1355534, BChE rs1803274, and ChAT rs2177369. The sample for the case-control study was 471 LOAD patients aged 60 years or older, and 254 subjects with no neurodegenerative disorders as the control group. A significant difference in the genotype distribution between patients and controls was observed only for ChAT rs2177369, showing that the G/G genotype was to be considered a risk factor with respect to the G/A + A/A genotypes (odds ratio = 1.56; 95% Confidence Interval = 1.10-2.22; P = 0.01). Though indicating a significant association with AD onset, our results are far from definitive since contrast with the ones reported by other authors in a previous case-control study, and call for further investigations. Among patients, 171 took part in an observational study concerning the possible role of the genetic composition on the efficacy of treatment with Donepezil and Rivastigmine. We related the SNPs of the above cited genes with cognitive status measured by MMSE. Carrying an allele or a genotype of these SNPs does not seem to play a relevant role in the response to treatment with the two cholinesterase inhibitors, though some significant results were found associated with the AChE A/A genotype that had the best response when treated with Rivastigmine.

A SNP in the ACT gene associated with astrocytosis and rapid cognitive decline in AD

There is biochemical and animal model evidence supporting a pathological role of the ACT gene in AD. However, direct genetic evidence remains controversial and has been mostly limited to individual single nucleotide polymorphism (SNP) analysis. To resolve this apparent conflict we have used a high-density ACT SNP map, constructed haplotypes and explored correlations with phenotype. SNPs were identified by sequencing and used to construct haplotypes in 668 AD patients and 419 controls and a case-control association study was performed. Five SNPs, comprising five common haplotypes, represented 93% of ACT gene variation. Although no single SNP or haplotype was associated with AD status, a SNP in intron 2 was associated with later onset and more rapid cognitive decline (P=0.04). This SNP was both individually associated with severe astrocytosis (P=0.004) in AD patients and when combined with the signal sequence SNP (P=0.002). This suggests that astrocytosis may have a protective function for a limited period in some patients. These SNP associations either support a direct role for the ACT gene, in AD pathology or alternatively reflect linkage with polymorphisms in other genes nearby.

Butyrylcholinesterase K variant associated with higher enzyme activity in the temporal cortex of elderly patients

There is evidence to suggest an involvement of the K variant of the butyrylcholinesterase gene (BCHE) in dementia. We have examined the relationship between BCHE genotype and butyrylcholinesterase (BuChE) activity in autopsy brain tissue. We studied 164 autopsy cases, 144 with dementia and 20 controls, including 13 K homozygotes and 48 K heterozygotes, from three centres: Newcastle, Oxford and London. Mean BuChE activity in temporal cortex was 37% higher in K homozygotes than in wild-type homozygotes. Linear regression analysis, controlling for gender, diagnosis, age at death and study centre, showed that the number of BCHE-K alleles was associated with increasing BuChE activity (p=0.009).

Meta-analysis of genetic variability in the beta-amyloid production, aggregation and degradation metabolic pathways and the risk of Alzheimer's disease

BACKGROUND

Variants in genes encoding enzymes involved in production, aggregation or degradation of beta-amyloid are potential risk factors for sporadic Alzheimer's disease (AD).

METHODS

Meta-analyses on AD association with BACE1 exon 5, BACE1 intron 5, FE65 intron 13, CYP46 intron 2, alpha(1)-antichymotrypsine Ala17Thr, bleomycin hydrolase I443V, lectin-like oxidized low-density lipoprotein receptor (OLR1) 3'-UTR (+1071) and (+1073), and very-low-density lipoprotein receptor (VLDLR) 5'-UTR (CGG-repeat) polymorphisms.

RESULTS

In BACE1 exon 5, genotype CC+CT acts as a protective factor in Apolipoprotein E (ApoE) epsilon 4 carriers [odds ratio (OR) = 0.57; 95% confidence interval (CI): 0.38-0.88], and as a risk factor in ApoE epsilon 4 non-carriers (OR = 1.33; 95% CI: 1.00-1.78). OLR1 3'-UTR (+1073) allele C is associated with increased risk (OR = 1.23; 95% CI: 1.01-1.50). VLDLR 5'-UTR genotype 2 is associated with increased risk (OR = 1.70; 95% CI: 1.09-2.63) in the Asian population and is protective (OR = 0.48; 95% CI: 0.26-0.86) in the non-Asian population. Other studied polymorphisms are not associated with AD.

CONCLUSIONS

The overall impact on AD risk of the genes for which meta-analyses are now available is rather limited. Additional meta-analyses of other different genes encoding for A beta production, aggregation and degradation mediators might help in determining the risk profile for AD.

Alzheimer's disease: case-control association study of polymorphisms in ACHE, CHAT, and BCHE genes in a Sardinian sample

Alzheimer's disease (AD) is characterized by an extensive loss of cholinergic neurons, and their cortical projections, from the basal forebrain area. The resulting reduction in cholinergic activity is associated with decreased levels of the neurotransmitter acetylcholine (ACh), decreased activity of acetylcholinesterase (AChE), choline acetyltransferase (ChAT), and increased butyrylcholinesterase (BChE) activity. In the present study, we investigated whether the BCHE, ACHE, and CHAT genes were associated with AD and the possibility of a synergistic effect with APOE-epsilon4 in a Sardinian sample. AD patients (n = 158), exclusively of Sardinian ancestry, were recruited from the Division of Geriatrics Local Health Agency 8 and Unit of Clinical Pharmacology, Department of Neurosciences, University of Cagliari. Patients were diagnosed according to DSM-IV, and National Institute of Neurologic and Communicative Disorders and Stroke-AD and Related Disorders Association (NINCDS-ADRDA) criteria for possible or probable AD. Cognitive screening was performed by means of Mini-Mental State Examination (MMSE). Healthy controls (n = 118) of Sardinian ancestry were recruited from religious and sport associations. All patients and control subjects gave informed consent for participation in the study. Single nucleotide polymorphism (SNP) analysis was performed by PCR/RFLP or the TaqMan 5' exonuclease method. Our study confirms the association between APOE epsilon4 allele and AD (P < 0.000). No significant differences were observed in allele and genotype frequencies of BCHE, ACHE, and CHAT between AD and controls. Haplotype analysis of ACHE SNPs did not reveal a significant association between ACHE and AD. Our results suggest that the AChE, ChAT, and BChE polymorphisms do not constitute a major genetic risk factor for susceptibility to AD in a Sardinian population.

Homozygosity for the K variant of BCHE gene increases the risk for development of neurofibrillary pathology but not amyloid deposits at young ages

The presence of the K variant of the butyrylcholinesterase gene (BCHE-K) has been associated with the severity of Alzheimer's disease (AD)-related neurofibrillary tangles (NFT) and amyloid beta-protein (Abeta). To examine the impact of BCHE-K on the development of initial NFT- and Abeta pathologies in young individuals below the age of 45 years a total of 124 cases (110 cases with NFT-only pathology, 14 cases with Abeta-only pathology) and 104 matched controls were genotyped for BCHE-K. Homozygosity for BCHE-K was highly overrepresented among NFT-only group (8.2%) compared with controls (1%, P = 0.02) or the Abeta-only group (0%). The prevalence of the K allele, however, was comparable among groups. These findings suggest that homozygosity, but not heterozygosity, for BCHE-K is a potential risk factor for the development of NFT pathology in young individuals implicating BCHE-K in the pathogenesis of early AD.

Association study and meta-analysis of Alzheimer's disease risk and presenilin-1 intronic polymorphism

Numerous studies have tested for associations between an intronic polymorphism (rs165932) of presenilin-1 (PS-1) gene and the risk of Alzheimer's disease (AD), but results have been conflicting. To throw light on this issue, we investigate the possible involvement of PS-1 genotype in a case-control study based on a relatively stable population in Spain and a meta-analysis of published studies. An examination was conducted of 85 patients with probable or possible AD, along with controls from the same community, by using an chi(2) test for homogeneity and a binary logistic regression model. For comparison purposes, a meta-analysis of data from all available published studies was assessed. In our patients, homozygosity of the allele 2 in the PS-1 gene increased for late-onset AD (OR 2.38, 95% CI 1.07-5.29, P<0.05). The presence of at least one allele of apoE was also associated with AD (OR 4.01, 95% CI 1.93-8.34, p<0.05). The regression model showed that, overall, the presence of the apoE epsilon 4 allele and the PS-1 2/2 genotype were independent factors for the development of AD in our sample. In our genotype-based meta-analysis, the PS-1 2/2 genotype was probably related with AD for the European sub-group (fixed effects model, OR 1.19, 95% CI 1.02-1.37, p<0.05), but there are many confusing factors between different studies. Presenilin-1 2/2 genotype is a risk factor for late onset Alzheimer disease in the Spanish population, and probably, for Europeans.

Comparison of cognitive functions between people with silent and wild-type butyrylcholinesterase

In the human brain, butyrylcholinesterase (BuChE) is expressed in neurons and glia. For example, many nuclei in the human thalamus, with projections to the cerebral cortex, contain a large number of neurons with intense BuChE activity. Thalamocortical projections subserve a variety of cognitive functions. Due to genetic mutations, there are individuals who do not have detectable BuChE activity (silent BuChE). While the prevalence of silent BuChE is only 1:100,000 in European and American populations, it is 1:24 in the Vysya community in Coimbatore, India. To examine whether there are differences in cognitive functions between individuals with silent BuChE and those expressing normal BuChE (wild-type), twelve healthy individuals with silent BuChE and thirteen healthy individuals with wild-type BuChE, all from the Vysya community in Coimbatore, were tested for cognitive function using the Automated Neuropsychological Assessment Metrics test battery. The silent BuChE group was slightly faster on simple reaction tasks, but slower on a visual perceptual matching task. Furthermore, discriminant function analyses correctly classified 11/12 silent and 8/13 wild-type BuChE subjects (76% correct classification overall) based on BuChE status. Different profiles of cognitive test performance between individuals with silent and wild-type BuChE were observed. These observations suggest a function for BuChE in cognition.

Systematic meta-analyses of Alzheimer disease genetic association studies: the AlzGene database

The past decade has witnessed hundreds of reports declaring or refuting genetic association with putative Alzheimer disease susceptibility genes. This wealth of information has become increasingly difficult to follow, much less interpret. We have created a publicly available, continuously updated database that comprehensively catalogs all genetic association studies in the field of Alzheimer disease (http://www.alzgene.org). We performed systematic meta-analyses for each polymorphism with available genotype data in at least three case-control samples. In addition to identifying the epsilon4 allele of APOE and related effects, we pinpointed over a dozen potential Alzheimer disease susceptibility genes (ACE, CHRNB2, CST3, ESR1, GAPDHS, IDE, MTHFR, NCSTN, PRNP, PSEN1, TF, TFAM and TNF) with statistically significant allelic summary odds ratios (ranging from 1.11-1.38 for risk alleles and 0.92-0.67 for protective alleles). Our database provides a powerful tool for deciphering the genetics of Alzheimer disease, and it serves as a potential model for tracking the most viable gene candidates in other genetically complex diseases.

Susceptibility groups for Alzheimer's disease (OPTIMA cohort): Integration of gene variants and biochemical factors

Information on gene variants and blood levels (APOE, BCHE-K, TF-C2, HFE-D, HFE-Y, ACE I/D, AR1; homocysteine, folate and vitamin B(12)) is available for participants in the Oxford Project to Investigate Memory and Ageing (OPTIMA) cohort (n=575). This information identified four risk sets for Alzheimer's disease (AD) using grade of membership analysis (GoM). Graded membership scores that relate individuals to each set are automatically generated. Sets I and III had low intrinsic risk. Set II had high intrinsic risk associated with multiple gene variants, e.g., APOE44/34. Set IV also had high intrinsic risk demonstrating low folate and B(12) levels. Membership in the high intrinsic risk sets was summed, coded as either close versus not close (>or=0.80 versus <0.80) and input into logistic models to predict relative risk: close resemblance multiplied risk 80-fold for possible AD before age 65 and 55-fold for probable or definite AD at ages 65-74. These findings implicate both biochemical and genetic factors in the risk for AD and further support dietary supplementation with folate and vitamin B(12) as a potential means to delay the onset of AD and/or its rate of progression.

Differential CSF butyrylcholinesterase levels in Alzheimer's disease patients with the ApoE epsilon4 allele, in relation to cognitive function and cerebral glucose metabolism

Butyrylcholinesterase (BuChE) is increased in the cerebral cortex of Alzheimer's disease (AD) patients, particularly those carrying epsilon4 allele of the apolipoprotein E gene (ApoE) and certain BuChE variants that predict increased AD risk and poor response to anticholinesterase therapy. We measured BuChE activity and protein level in CSF of eighty mild AD patients in relation to age, gender, ApoE epsilon4 genotype, cognition and cerebral glucose metabolism (CMRglc). BuChE activity was 23% higher in men than women (p<0.03) and 40-60% higher in ApoE epsilon4 negative patients than in those carrying one or two epsilon4 alleles (p<0.0004). CSF BuChE level correlated with cortical CMRglc. Patients with high to moderate CSF BuChE showed better cognitive function scores than others. We hypothesize that CSF BuChE varies inversely with BuChE in cortical amyloid plaques. Thus, low BuChE in a patient's CSF may predict extensive incorporation in neuritic plaques, increased neurotoxicity and greater central neurodegeneration.

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.

Lipid homeostasis and apolipoprotein E in the development and progression of Alzheimer's disease

Extracellular amyloid plaques, intracellular neurofibrillary tangles, and loss of basal forebrain cholinergic neurons in the brains of Alzheimer's disease (AD) patients may be the end result of abnormalities in lipid metabolism and peroxidation that may be caused, or exacerbated, by beta-amyloid peptide (Abeta). Apolipoprotein E (apoE) is a major apolipoprotein in the brain, mediating the transport and clearance of lipids and Abeta. ApoE-dependent dendritic and synaptic regeneration may be less efficient with apoE4, and this may result in, or unmask, age-related neurodegenerative changes. The increased risk of AD associated with apoE4 may be modulated by diet, vascular risk factors, and genetic polymorphisms that affect the function of other transporter proteins and enzymes involved in brain lipid homeostasis. Diet and apoE lipoproteins influence membrane lipid raft composition and the properties of enzymes, transporter proteins, and receptors mediating Abeta production and degradation, tau phosphorylation, glutamate and glucose uptake, and neuronal signal transduction. The level and isoform of apoE may influence whether Abeta is likely to be metabolized or deposited. This review examines the current evidence for diet, lipid homeostasis, and apoE in the pathogenesis of AD. Effects on the cholinergic system and response to cholinesterase inhibitors by APOE allele carrier status are discussed briefly.

Rate of progression of cognitive decline in Alzheimer's disease: effect of butyrylcholinesterase K gene variation

OBJECTIVE

To determine whether individuals with Alzheimer's disease (AD) and the K variant allele of butyrylcholinesterase have a slower rate of cognitive decline than those without the K variant allele of butyrylcholinesterase.

METHOD

The cognitive status of 339 community based subjects with AD was assessed with the Mini Mental State Examination at baseline and yearly over a three year follow up period. The rates of cognitive decline of subjects with and without the K variant allele were compared.

RESULT

Presence of the K allele was associated with a slower average rate of cognitive decline in subjects with severe AD.

CONCLUSIONS

This finding is consistent with the suggestion that the K variant of butyrylcholinesterase has an important role in disease progression in AD, and this may have implications for treatment.

Association between apolipoprotein E polymorphism and Alzheimer disease in Tehran, Iran

Epsilon 4 allele of apolipoprotein E (APOE-epsilon4) is a major risk factor for Alzheimer's disease (AD). The association of APOE allele frequencies with AD remains unknown in developing countries. We examined the frequency of APOE alleles in 105 patients with AD and 129 cognitively normal subjects of similar age and sex (control group), in Tehran, Iran. The APOE-epsilon4 allele frequency was significantly higher in the AD subjects than in the control group (21% versus 6.2%, p < 0.001). In addition, the OR for APOE-epsilon4 heterozygous and homozygous subjects were 3.2 (p = 0.001) and 12.75 (p = 0.01), respectively. The OR was not uniform across age groups. The AD subjects carrying one or two APOE-epsilon4 allele showed earlier age-at-onset (p < 0.001). These data suggest that the APOE-epsilon4 allele increase the risk for AD in Tehran population in a dose and age-dependent manner. Although the APOE-epsilon2 allele frequency was lower in the AD subjects than in the control group (0.95% versus 2.7%, p = 0.15), APOE-epsilon2 was not associated with the onset of AD in Tehran's population. The OR for epsilon2 allele in AD subjects was 0.34 (p = 0.21). The genotype frequencies for epsilon3, epsilon4, and epsilon2 alleles in control subjects were 91.2, 6.1, and 2.7%, respectively. These values were similar to that reported for Turkish, Greece, Japanese, Spanish, and Moroccan populations, but they were significantly different from the reported values for the other ethnic populations. This observation emphasizes the importance of geographical location and ethnical background of the subjects in the study of APOE genotypes and their association with AD.

Analysis of association between butyrylcholinesterase K variant and apolipoprotein E genotypes in Alzheimer's disease

Recent studies indicate that there is a synergic association between butyrylcholinesterase-K variant (BChE-K) and apolipoproteinE-epsilon 4 (ApoE-epsilon 4) to promote risk for Alzheimer's disease (AD). Most subsequently replicative studies have been unable to confirm these finding. We attempted to replicate this finding in 105 AD cases and age and sex matched 129 controls from Tehran population, Iran. The BChE genotype of patients were found to be significantly different from controls (chi(2) = 12.2, d.f. = 2, p = 0.002). The frequency of BChE-K allele was also found to differ significantly in cases compared to controls [24% versus 12% (chi(2) = 20.6, d.f. = 2, p < 0.001)] leading to an increased risk of AD in subjects with this allele (OR = 2.5, 95% CI = 1.64-3.8, p = 0.001). This risk was found to increase from (OR = 2.37, 95% CI = 1.3-4.2, p = 0.006) in subjects less than 75 years old to (OR = 3.16, 95% CI = 1.41-7.1, p = 0.001) in subjects 75 years and older. But, the ApoE-epsilon 4 allele association risk was found to decrease from (OR = 9.5, 95% CI = 3.74-24.1, p = 0.001) in subjects <75 years to (OR = 1.36, 95% CI = 0.49-4.1, p = 0.58) in those subjects 75 years and older. Furthermore, we found a very strong synergic association between BChE-K and ApoE-epsilon 4 OR = 19.1 (95% CI = 428-85.45, p < 0.001). In spite of this, synergism decreased from OR = 36.2 (95% CI = 4.4-296, p = 0.001) in subjects <75 year olds to OR = 6.2 (95% CI = 0.9-72.4, p = 0.06) in subjects > or =75 years. We have found that BChE-K and ApoE-epsilon 4 alleles act synergistically to increase the risk of the late-onset AD, particularly in age group <75 years in Tehran, Iran.

Modest implication of interleukin-6 promoter polymorphisms in longevity

The multifunctional interleukin-6 has been suggested to contribute to a chronic low-grade inflammatory status, thereby conferring susceptibility to age-related pathological conditions as well as functional decline and increased mortality. Several polymorphisms have been identified in the interleukin-6 promoter, but investigation of the effect of these on interleukin-6 levels and disease susceptibility have led to contradictory results. This study investigates the significance of the three single-point polymorphisms (-597G/A, -572G/C and -174G/C) and the AT-stretch polymorphism (-373(A)n(T)m) in ageing, by comparison of the frequency of each single polymorphism separately as well as the entire promoter haplotype in a total of 1710 Danish subjects ranging in age from 47 to 100 years. We found a modest, but significant, increase in the frequency of interleukin-6 -174GG homozygotes with age suggesting that this genotype is advantageous for longevity.

Candidate gene association studies of genes involved in neuronal cholinergic transmission in Alzheimer's disease suggests choline acetyltransferase as a candidate deserving further study

Consistent deficits in the cholinergic system are evident in the brains of Alzheimer's Disease (AD) patients, including reductions in the activities of acetylcholine, acetylcholinesterase (AChE), and choline acetyltransferase (ChAT), increased butyrylcholinesterase (BChE) activity, and a selective loss of nicotinic acetylcholine receptors (nAChRs). Accordingly, we have analyzed polymorphisms in the genes encoding AChE, ChAT, BChE, and several of the subunit genes from neuronal nAChRs, for genetic associations with late-onset AD. A significant association for disease was detected for a non-coding polymorphism in ChAT (allele chi(1) (2) = 12.84, P = 0.0003; genotype chi(2) (2) = 11.89, P = 0.0026). Although replication analysis did not confirm the significance of this finding when the replication samples were considered alone (allele chi(1) (2) = 1.02, P = 0.32; genotype chi(2) (2) = 1.101, P = 0.58) the trends were in the correct direction and a significant association remained when the two sample sets were pooled (allele chi(1) (2) = 12.37, P = 0.0004; genotype chi(2) (2) = 11.61, P = 0.003). Previous studies have reported significant disease associations for both the K-variant of BChE and the coding ChAT rs3810950 polymorphism with AD. Replication analyses of these two loci failed to detect any significant association for disease in our case-control samples.

Differential qualitative responses to rivastigmine in APOE ɛ4 carriers and noncarriers

This retrospective analysis of two double-blind, placebo-controlled studies in patients with mild to moderately severe AD investigated the efficacy of rivastigmine 6-12 mg/day on cognitive outcomes in patients with or without the apolipoprotein (APOE) epsilon4 allele. APOE data were collected from patients who consented to pharmacogenetic testing. Treatment differences within each subgroup were compared, using the Observed Case (OC) population. The APOE epsilon4 and non-APOE epsilon4 subgroups comprised 246 and 121 patients, respectively. Overall, APOE epsilon4 noncarriers showed greater decline than carriers (P<0.05). However, at 26 weeks, placebo-treated APOE epsilon4 patients declined 3.04 points below baseline on the cognitive subscale of the Alzheimer's Disease Assessment Scale (ADAS-cog), and rivastigmine-treated patients improved by 1.67 points. Non-APOE epsilon4 placebo-treated patients declined by 4.59 points and rivastigmine-treated patients declined by 0.48 points. Thus, non-APOE epsilon4 carriers showed a less favorable course under either placebo or rivastigmine, but both genotype-defined subgroups showed quantitatively similar responses to therapy (both P<0.05 vs placebo).

Large-scale studies of the functional K variant of the butyrylcholinesterase gene in relation to Type 2 diabetes and insulin secretion

AIMS/HYPOTHESIS

Polymorphisms of the butyrylcholinesterase gene (BCHE) are reported to associate with Alzheimer's disease and a recent study found a significant association of the BCHE K variant (G1615A/Ala539Thr) with Type 2 diabetes. The objectives of our study were to examine whether the BCHE K variant is associated with Type 2 diabetes or estimates of pancreatic beta cell function in large-scale populations of glucose-tolerant Caucasians.

METHODS

The variant was genotyped in association studies comprising a total of 1408 Type 2 diabetic patients and 4935 glucose-tolerant control subjects. Genotype-phenotype studies were carried out in the 4935 glucose-tolerant control subjects.

RESULTS

There was no difference in allele frequency between Type 2 diabetic patients and control subjects (20.3% [95% confidence interval: 18.8-21.8] vs 20.4% [19.6-21.2], non-significant). In the genotype-phenotype studies we found no consistent association with BMI, fasting or post-OGTT plasma glucose, serum insulin or serum C-peptide levels.

CONCLUSIONS/INTERPRETATION

The present study does not support the suggestion that the BCHE K polymorphism is associated with Type 2 diabetes or with estimates of pancreatic beta cell function in large-scale Danish Caucasian populations.

Synergy between the C2 allele of transferrin and the C282Y allele of the haemochromatosis gene (HFE) as risk factors for developing Alzheimer's disease

BACKGROUND

There is evidence that iron may play a role in the pathology of Alzheimer's disease (AD). There may be genetic factors that contribute to iron deposition resulting in tissue damage thus exacerbating AD.

METHODS

We have genotyped 269 healthy elderly controls, 191 cases with definite or probable AD, and 69 with mild cognitive impairment (MCI) from the OPTIMA cohort.

RESULTS

We have examined the interaction between the C2 variant of the transferrin (TF) gene and the C282Y allele of the haemochromatosis (HFE) gene as risk factors for developing AD. Our results showed that each of the two variants was associated with an increased risk of AD only in the presence of the other. Neither allele alone had any effect. Carriers of both variants were at 5 times greater risk of AD compared with all others. The interaction was significant by logistic regression (p = 0.014) and by synergy factor analysis (p = 0.015, synergy factor = 5.1). Further, carriers of these two alleles plus apolipoprotein E epsilon4 (APOE4) were at still higher risk of AD: of the 14 tri-carriers of the three variants, identified in this study, 12 had AD and two MCI.

CONCLUSION

We suggest that the combination of TF C2 and HFE C282Y may lead to an excess of redox-active iron and the induction of oxidative stress in neurones, which is exacerbated in carriers of APOE4. Since 4% of Northern Europeans carry the two iron-related variants and since iron overload is a treatable condition, these results merit replication.

Age-dependent association between the Q7R polymorphism in the Saitohin gene and sporadic Alzheimer's disease

A vigorous controversy exists over whether tau tangles or amyloid-beta plaques are the primary cause of neurodegeneration in Alzheimer's disease (AD), and it is not well established whether genetic variation in tau is associated with AD. A recently identified novel protein, named Saitohin (STH), shares tissue expression pattern with tau, and preliminary evidence in a North American population indicates that a polymorphism at codon 7 (Q7R) of the STH gene is a predisposing factor for sporadic AD. A case-control study utilizing a clinically well-defined group of 315 sporadic AD patients and 307 control subjects was performed to test this association. The current study reveals that increased risk of AD associated with the STH RR genotype (OR 2.17, p = 0.04) is limited to late-onset (after the age of 72 years) AD cases.

Association of the androgen receptor CAG repeat polymorphism with Alzheimer's disease in men

We examined the CAG repeat polymorphism in exon 1 of the androgen receptor (AR) in an Oxford cohort of 150 cases (101 men) of definite or probable Alzheimer's disease (AD) and 190 elderly controls (140 men). We found that short alleles (< or = 20 CAG repeats) were associated with AD (adjusted odds ratio = 2.5, 95% confidence intervals: 1.2-5.0) in men, but not in women. This association appeared stronger in early-onset AD (< 65 years). We conclude that this AR polymorphism is of potential relevance to the risk of AD in men.