<Emphasis Type="Italic">APOE</Emphasis> ε4 lowers age at onset and is a high risk factor for Alzheimer's disease; A case control study from central Norway

Background

The objective of this study was to analyze factors influencing the risk and timing of Alzheimer's disease (AD) in central Norway. The APOE ε4 allele is the only consistently identified risk factor for late onset Alzheimer's disease (LOAD). We have described the allele frequencies of the apolipoprotein E gene (APOE) in a large population of patients with AD compared to the frequencies in a cognitively-normal control group, and estimated the effect of the APOE ε4 allele on the risk and the age at onset of AD in this population.

Methods

376 patients diagnosed with AD and 561 cognitively-normal control individuals with no known first degree relatives with dementia were genotyped for the APOE alleles. Allele frequencies and genotypes in patients and control individuals were compared. Odds Ratio for developing AD in different genotypes was calculated.

Results

Odds Ratio (OR) for developing AD was significantly increased in carriers of the APOE ε4 allele compared to individuals with the APOE ε3/ε3 genotype. Individuals carrying APOE ε4/ε4 had OR of 12.9 for developing AD, while carriers of APOE ε2/ε4 and APOE ε3/ε4 had OR of 3.2 and 4.2 respectively. The effect of the APOE ε4 allele was weaker with increasing age. Carrying the APOE ε2 allele showed no significant protective effect against AD and did not influence age at onset of the disease. Onset in LOAD patients was significantly reduced in a dose dependent manner from 78.4 years in patients without the APOE ε4 allele, to 75.3 in carriers of one APOE ε4 allele and 72.9 in carriers of two APOE ε4 alleles. Age at onset in early onset AD (EOAD) was not influenced by APOE ε4 alleles.

Conclusion

APOE ε4 is a very strong risk factor for AD in the population of central Norway, and lowers age at onset of LOAD significantly.

     

Association of APOE, GCPII and MMP9 polymorphisms with common diseases and lipid levels in an older adult/elderly cohort

Background and aims

The characterization of candidate gene polymorphisms in elderly populations is an important tool for the identification of risk factors for age-related diseases and conditions. We aimed to genotype the APOE polymorphisms (rs429358 and rs7412), rs61886492 (1561C>T) and rs202720 of GCPII gene and rs3918242 (− 1562C>T) of MMP9 gene in an older-adult/elderly cohort from Cuiabá city, Mato Grosso Brazil as well as to characterize risk factors for morbidities and conditions affecting this cohort.

Methods

The studied population consisted of 570 subjects from Cuiabá city, Brazil, who were subjected to clinical interviews and blood collection for laboratory examinations and DNA extraction. Restriction Fragment Length Polymorphism Polymerase Chain Reaction (RFLP-PCR), sequence-specific primer PCR (SSP-PCR) and TaqMan® allelic discrimination assay were used for genotyping.

Results

The frequencies of APOE ε2 and ε4 were 6.6% and 14.8%, respectively, and the frequencies of GCPII rs61886492 T allele, GCPII rs202720 C allele and MMP9 rs3918242 T allele were, respectively, 3.0%, 26.6% and 10.1%. Significant associations between APOE ε2 allele with lower total cholesterol and LDL-cholesterol were found. In addition, MMP9 rs3918242 T allele was associated with higher LDL-cholesterol levels, suggesting a link between lipid metabolism alteration and cardiovascular disease.

Conclusions

The present findings contributed to characterize risk factors specific for the studied population and to better understand the molecular physiopathology of common morbidities and conditions affecting older-adult/elderly people.     

The synergistic risk effect of apolipoprotein ε4 and DNA (cytosine-5-)-methyltransferase 3 beta (<Emphasis Type="Italic">DNMT3B</Emphasis>) haplotype for Alzheimer’s disease

Alzheimer’s disease (AD) is a complex and multifactorial disease with the contribution of several genes and polymorphisms to its development. Among these genes, the APOEε4 is the best known risk factor for AD. Methylation is associated with APOE expression and AD development. Recently, we found an association of the TGG haplotype in the DNMT3B gene, one of the catalyst enzyme for methylation, with AD. Therefore, the objective of the study was to investigate whether APOEε4 and TGG haplotype have an synergistic effect on AD. The sample was composed of 212 Caucasian individuals (108 healthy controls and 104 with AD by NINCDS-ADRDA and DSM-IV-TR criteria) from southern Brazil. The genetic analyses were performed by real time PCR for TaqMan^® assay. Multivariate logistic regression was performed categorizing groups according to presence of APOEε4 and/or TGG haplotype as an independent variable for outcome AD. The presence of TGG haplotype plus the allele APOEε4 were strongly associated with AD [OR 11.13; 95 % CI (4.25–29.16); P < 0.001]. This association had a higher risk than each risk factor alone. We found a strong association of the interaction of DNMT3B gene with the APOEε4 in this sample of AD patients. The presence of TGG haplotype and APOEε4 significantly increased the risk of developing the disease, showing an synergistic effect.     

Apolipoprotein E polymorphism and the risk of aneurysmal subarachnoid hemorrhage in a South Indian population

Background

The rupture of a brain aneurysm causes bleeding in the subarachnoid space. This is known as aneurysmal subarachnoid hemorrhage (aSAH). We evaluated the association of apolipoprotein E (APOE) polymorphism and the risk of aSAH in a South Indian population.

Methods

The study was performed on 200 subjects with aSAH and 253 healthy control subjects. Blood samples (5 ml) were used to isolate DNA and genotyping was performed for rs7412 and rs429358 using a Taqman allelic discrimination assay. Statistical software R.3.0.11 was used to statistically analyze the data and a p value <?0.05 was considered as statistically significant.

Results

We found a significant association with the risk of aSAH in ε3/ ε4 genetic model (OR?=?1.91, 95% CI?=?1.16–3.14, p?=?0.01). However, in the other genetic models and allele frequency, there was no significant association with the risk of aSAH. In subtyping, we found a significant association of ε2 allele frequency with posterior communicating artery (PCOM) aneurysm (OR?=?3.59, 95% CI?=?1.11–11.64, p?=?0.03).

Conclusion

Our results suggest that APOE polymorphism has an influence on the risk of aSAH in this South Indian population, specifically in the PCOM subtype.

     

A Missense Variant in <Emphasis Type="Italic">TREML2</Emphasis> Reduces Risk of Alzheimer’s Disease in a Han Chinese Population

Recently, Benitez and colleagues re-analyzed whole-exome sequencing data and revealed that a coding missense variant (rs3747742-C) in triggering receptor expressed on myeloid cells-like 2 (TREML2) gene reduced late-onset Alzheimer’s disease (LOAD) risk in Caucasians. To date, no study was carried out to test this association in other ethnic groups and populations, including Han Chinese. Therefore, the aim of the current study was to validate the relation between rs3747742 and LOAD susceptibility in a large Han Chinese population including 992 LOAD patients and 1358 healthy controls. In the total sample, the minor (C) allele of rs3747742 was associated with a reduced LOAD risk under the recessive genetic model after Bonferroni correction (odds ratio (OR)?=?0.713; 95 % confidence interval (CI): 0.546–0.932; P?=?0.013, Bonferroni-corrected P?=?0.039). Interestingly, after stratifying data according to apolipoprotein E (APOE) ε4 status, we revealed that this protection only exists in APOE ε4 carriers (recessive genetic model, OR?=?0.448; 95 % CI: 0.262–0.765; P?=?0.003, Bonferroni-corrected P?=?0.009) in our cohort. Taken together, our findings support rs3747742-C as a protective factor for LOAD, especially in APOE ε4 carriers.     

Associations of rs3740677 within <Emphasis Type="Italic">GAB2</Emphasis> Gene with LOAD in Chinese Han Population

GRB2-associated binding protein 2 (GAB2) has been identified as a crucial factor in Alzheimer’s disease (AD), and ten common variants within GAB2 have been detected to be associated with AD onset risk in genome-wide association studies (GWAS). Here, we first screened a common locus (rs3740677) in 3′ UTR of GAB2 sequence which is targeted by the miRNA-185 and initiatively explored the probable associations of rs3740677 with risk for late-onset AD (LOAD) in a large scale case–control study from Chinese Han populations (992 LOAD patients and 1358 healthy subjects). Eventually, the genotype (P?=?0.024) and allele (P?=?0.008) distribution of rs3740677 showed significant difference between LOAD and control group, and we observed a significant association of T allele in rs3740677 with LOAD risk in multivariate analysis and it decreased the risk for LOAD (dominant: OR?=?0.831, 95 % CI?=?0.702–0.983, P?=?0.031; additive: OR?=?0.855, 95 % CI?=?0.745–0.983, P?=?0.027) adjusted for age, gender, and APOE ε4 status. Our study further confirmed the association of GAB2 and AD. However, the absolute and correct association of rs3740677 with AD still required more investigations in diverse regions and ethnics.     

Genetic cross-interaction between APOE and PRNP in sporadic Alzheimer's and Creutzfeldt-Jakob diseases

Alzheimer''s disease (AD) and Creutzfeldt-Jakob disease (CJD) represent two distinct clinical entities belonging to a wider group, generically named as conformational disorders that share common pathophysiologic mechanisms. It is well-established that the APOE ε4 allele and homozygosity at polymorphic codon 129 in the PRNP gene are the major genetic risk factors for AD and human prion diseases, respectively. However, the roles of PRNP in AD, and APOE in CJD are controversial. In this work, we investigated for the first time, APOE and PRNP genotypes simultaneously in 474 AD and 175 sporadic CJD (sCJD) patients compared to a common control population of 335 subjects. Differences in genotype distribution between patients and control subjects were studied by logistic regression analysis using age and gender as covariates. The effect size of risk association and synergy factors were calculated using the logistic odds ratio estimates. Our data confirmed that the presence of APOE ε4 allele is associated with a higher risk of developing AD, while homozygosity at PRNP gene constitutes a risk for sCJD. Opposite, we found no association for PRNP with AD, nor for APOE with sCJD. Interestingly, when AD and sCJD patients were stratified according to their respective main risk genes (APOE for AD, and PRNP for sCJD), we found statistically significant associations for the other gene in those strata at higher previous risk. Synergy factor analysis showed a synergistic age-dependent interaction between APOE and PRNP in both AD (SF = 3.59, p = 0.027), and sCJD (SF = 7.26, p = 0.005). We propose that this statistical epistasis can partially explain divergent data from different association studies. Moreover, these results suggest that the genetic interaction between APOE and PRNP may have a biological correlate that is indicative of shared neurodegenerative pathways involved in AD and sCJD.     

Mitochondrial DNA haplogroups in early-onset Alzheimer's disease and frontotemporal lobar degeneration

Background

Alleles of apolipoprotein E (APOE) are the major genetic risk factor for late onset Alzheimer's Disease (LOAD). Recently, an APOE splice variant that retains intron 3 (APOE-I3) was identified. To gain insight into the possible role of this isoform in LOAD, we quantified its expression in a cohort of 56 human brain specimens by using quantitative RT-PCR.

Results

We found that APOE-I3 generally represents a low percentage (< 0.5%) of overall APOE expression. However, in one specimen, the proportion of APOE-I3 was increased about ~13 fold. This specimen was unique in the cohort for possessing the minor allele of an intron 3 single nucleotide polymorphism (SNP), rs12982192. Additionally, an allelic expression imbalance study indicated that the rs12982192 minor allele was associated with increased APOE-I3 expression.

Conclusions

Overall, we interpret our results as suggesting that APOE-I3 represents a minor portion of APOE expression and that rs12982192 is associated with APOE intron 3 retention. Since the minor allele of this SNP is on the same haplotype as the minor allele of rs429358, which defines the APOE4 allele, we speculate that rs12982192 may reflect a modest loss of mRNA encoding functional APOE4.     

Effect of APOE and CD33 on Cognitive Decline

ObjectiveAn Alzheimer’s disease (AD) diagnosis is preceded by a long period of cognitive decline. We previously demonstrated increased risk of decline among individuals possessing one or more APOE ε4 alleles together with a family history of AD. The objective of this study is to investigate the possibility that such an increased risk might be due to AD risk genes with small effects in combination with APOE.MethodsParticipants in the Health and Retirement Study (HRS) over the age of 65, who contributed DNA, and had two or more evaluations with an abbreviated version of the modified Telephone Interview for Cognitive Status (TICS-m) were eligible for the study (n = 7451). A genetic risk score (g-score) was derived using AD risk genes’ meta-analyses data, assigning risk according to the number of risk alleles and summed over all the risk genes. Trajectories of cognitive function were modeled in four groups of Caucasian participants with and without one or more APOE ε4 alleles and either a high or low g-score: APOE ε4-/low g-score; APOE ε4-/high g-score; APOE ε4+/low g-score; and APOE ε4+/high g-score. Post hoc analyses evaluated interactions between individual genes and APOE.ResultsIndividuals in the APOE ε4+/high g-score group exhibited the greatest cognitive decline over time (p<.0001). This risk appeared to be greater than the sum of the effects of either high g-score or APOE ε4 alone. When gene interactions were individually tested with APOE, a statistically significant interaction with CD33 was discovered (p = 0.04) although the interaction was no longer significant when adjusted for multiple comparisons.ConclusionsIndividuals with multiple AD risk genes in addition to having one or more APOE ε4 alleles are at greater risk of cognitive decline than individuals with either APOE ε4 or a high genetic risk score. Among those with one or more APOE ε4 alleles, having one or more copies of the CD33 C (risk) allele may further increase the risk of cognitive decline.     

Association Between Apolipoprotein E Gene Polymorphism and Myocardial Infarction

We investigated apolipoprotein E (APOE) genotypic influence on myocardial infarction risk in South India, where the disease is emerging as a major threat to the public health care system. The study included 412 subjects: 202 myocardial infarction patients and 210 age- and sex-matched controls. DNA was isolated, the polymorphism of the APOE gene was subjected to PCR, and lipid levels were evaluated. The prevalence of E3/E4 genotypes in patients (18.3%) was 1.5-fold that of controls (11.0%, p < 0.05), and the prevalence of E2/E3 genotypes was higher in controls (6.7%) than in patients (4%). The ε4 allele was significantly associated with myocardial infarction: χ ² = 12.4; OR 2.2 (CI 95%: 1.4–3.4), p < 0.004, for ε4 versus ε3 and χ ² = 5.7; OR 2.7 (CI 95%: 1.1–6.5), p > 0.01, for ε4 versus ε2. A significant association of the ε4 allele, especially the E3/E4 genotype, with myocardial infarction was observed.     

Ubiquitin carboxy-terminal hydrolase L1 (UCHL1) S18Y polymorphism in Alzheimer's disease

Alzheimer's disease (AD) is characterized by protein aggregates, i.e. senile plaques and neurofibrillary tangles. The ubiquitin-proteasome system has been proposed a role in proteolytic removal of these protein aggregates. Ubiquitin carboxy-terminal hydrolase L1 (UCHL1) is a de-ubiquitinating enzyme with important functions in recycling of ubiquitin. The S18Y polymorphism of the UCHL1 gene confers protection against Parkinson's disease. In this study, the genotype and allele frequencies of the UCHL1 S18Y polymorphism were investigated in 452 AD patients and 234 control subjects, recruited from four memory clinics in Sweden. Using a binary logistic regression model including UCHL1 allele A and APOE ε4 allele positivity, age and sex as covariates with AD diagnosis as dependent variable, an adjusted OR of 0.82 ([95% CI 0.55-1.24], P = 0.35) was obtained for a positive UCHL1 allele A carrier status. The present study thus do not support a protective effect of the UCHL1 S18Y polymorphism against AD.     

Allelic variation within the major APOE CpG island affects its methylation in the brain of targeted replacement mice expressing human APOE

• •The number of cytosine-phosphate-guanine (CpG) sites differs due to sequence variation in the human apolipoprotein E (APOE) gene.
• •APOE DNA methylation is allele-dependently altered corresponding to the total number of CpG pairs in the brain of APOE targeted replacement mice (APOE εpsilon 4 > εpsilon 3 > εpsilon 2).
• •Binding of the methyl-CpG binding protein 2 to genomic APOE was in trend less pronounced in the brain of APOE4 mice.

     

The Involvement of Lipids in Alzheimer's Disease

It has been estimated that Alzheimer＇s disease （AD）, the most common form of dementia, will affect approximately 81 million individuals by 2040. To date, the actual cause and cascade of events in the progression of this disease have not been fully determined. Furthermore, there is currently no definitive blood test or simple diagnostic method for AD. Considerable efforts have been put into proteomic approaches to develop a diagnostic blood test, but to date these efforts have not been successful. More recently, there has been a stronger focus on lipidomic studies in the hope of increasing our understanding of the underlying mechanisms leading to AD and developing an AD blood test. It is well known that the strongest genetic risk factor for AD is the e4 variant of apolipoprotein E （APOE）. Evidence suggests that the ApoE protein, a major lipid transporter, plays a key role in the pathogenesis of AD, and its role in both normal and aberrant lipid metabolism warrants further extensive investigation. Here, we review ApoE-lipid interactions, as well as the roles that lipids may play in the pathogenesis of AD.     

Volume of white matter hyperintensities in healthy adults: Contribution of age, vascular risk factors, and inflammation-related genetic variants

Aging is associated with appearance of white matter hyperintensities (WMH) on MRI scans. Vascular risk and inflammation, which increase with age, may contribute to white matter deterioration and proliferation of WMH. We investigated whether circulating biomarkers and genetic variants associated with elevated vascular risk and inflammation are associated with WMH volume in healthy adults (144 volunteers, 44-77 years of age). We examined association of WMH volume with age, sex, hypertension, circulating levels of total plasma homocysteine (tHcy), cholesterol (low-density lipoprotein), and C-reactive protein (CRP), and four polymorphisms related to vascular risk and inflammation: Apolipoprotein ε (ApoE ε2,3,4), Angiotensin-Converting Enzyme insertion/deletion (ACE I/D), methylenetetrahydrofolate reductase (MTHFR) C677T, C-reactive protein (CRP)-286C>A>T, and interleukin-1β (IL-1β) C-511T. We found that larger WMH volume was associated with advanced age, hypertension, and elevated levels of homocysteine and CRP but not with low-density lipoprotein levels. Homozygotes for IL-1β-511T allele and carriers of CRP-286T allele that are associated with increased inflammatory response had larger WMH than the other allelic combinations. Carriers of the APOE ε2 allele had larger frontal WMH than ε3 homozygotes and ε4 carriers did. Thus, in healthy adults, who are free of neurological and vascular disease, genetic variants that promote inflammation and elevated levels of vascular risk biomarkers can contribute to brain abnormalities. This article is part of a Special Issue entitled: Imaging Brain Aging and Neurodegenerative disease.     

Biochip for determination of genetic markers of sporadic Alzheimer’s disease risk in the Russian Slavic population

A biological microchip (biochip) has been developed to study the genetic predisposition to sporadic form of Alzheimer’s disease (AD). The biochip allows of genotyping of ten genetic polymorphisms within APOE, TOMM40, APOJ, EXOC3L2, GAB2, A2M, CR1, BIN1, and PICALM genes. The assay includes the amplification of the loci of interest and subsequent allele-specific hybridization of the fluorescently labeled amplicons with oligonucleotides immobilized on the biochip. The genotyping of 166 patients and 128 controls revealed a significant association of APOE allele ?4 with susceptibility to AD (OR = 2.275, 95% CI 1.045–4.954, p = 0.034). Protective effects were observed for APOE allele ?2 and CLU (rs11136000) allele T (OR = 0.215, 59% CI 0.090–0.516, p = 0.001 and OR = 0.679, 95% CI 0.47–0.99, p = 0.042, respectively). A gene-gene interaction analysis revealed two AD-associated genotype combinations, APOE ?3/?4 GAB2 G/G (OR = 2.49, 95% CI 1.43–4.32, p = 0.001) and APOE ?4/?4 GAB2 G/G (OR = 3.55, 95% CI 1.23–10.24, p = 0.015). Based on the results of the combined multivariate analysis, an algorithm was developed to identify the individuals having a higher risk of AD.     

PRND 3′UTR polymorphism may be associated with behavioral disturbances in Alzheimer disease

The etiology of behavioral and psychological symptoms of dementia (BPSD) is complex, including putative biological, psychological, social and environmental factors. Recent years have witnessed accumulation of data on the association between genetic factors and behavioral abnormalities in Alzheimer disease (AD). In this research paper, our aim is to evaluate the association between the APOE, CYP46, PRNP and PRND genes and the profile of neuropsychiatric symptoms in Polish subjects with AD and mild cognitive impairment (MCI). We studied 99 patients with AD and 48 subjects with MCI. The presence and profile of BPSD were evaluated at baseline and prospectively with the Neuropsychiatric Inventory (NPI). Patients were dichotomized into those having ever experienced a particular symptom and those who did not over the whole disease period. Genotyping was performed using previously described standard protocols. The prevalence of comorbid behavioral symptoms and the overall level of behavioral burden were significantly greater in AD compared with the MCI group. In AD patients, carrier status of the T allele of the 3′UTR (untranslated region) PRND polymorphism was associated with an increased cumulative behavioral load and an elevated risk for delusions, anxiety, agitation/aggression, apathy and irritability/emotional ability. Among MCI subjects, APOE ε4 carriers demonstrated a reduced risk for nighttime behavior change. No other statistically significant genotype-phenotype correlations were observed, including the APOE, CYP46 and PRNP genes. A precise estimation of the exact significance of particular polymorphisms in BPSD etiology requires future studies on large populations.     

Resting-State Network Disruption and APOE Genotype in Alzheimer's Disease: A lagged Functional Connectivity Study

Background

The apolipoprotein E epsilon 4 (APOE-4) is associated with a genetic vulnerability to Alzheimer''s disease (AD) and with AD-related abnormalities in cortical rhythms. However, it is unclear whether APOE-4 is linked to a specific pattern of intrinsic functional disintegration of the brain after the development of the disease or during its different stages. This study aimed at identifying spatial patterns and effects of APOE genotype on resting-state oscillations and functional connectivity in patients with AD, using a physiological connectivity index called “lagged phase synchronization”.

Methodology/Principal Findings

Resting EEG was recorded during awake, eyes-closed state in 125 patients with AD and 60 elderly controls. Source current density and functional connectivity were determined using eLORETA. Patients with AD exhibited reduced parieto-occipital alpha oscillations compared with controls, and those carrying the APOE-4 allele had reduced alpha activity in the left inferior parietal and temporo-occipital cortex relative to noncarriers. There was a decreased alpha2 connectivity pattern in AD, involving the left temporal and bilateral parietal cortex. Several brain regions exhibited increased lagged phase synchronization in low frequencies, specifically in the theta band, across and within hemispheres, where temporal lobe connections were particularly compromised. Areas with abnormal theta connectivity correlated with cognitive scores. In patients with early AD, we found an APOE-4-related decrease in interhemispheric alpha connectivity in frontal and parieto-temporal regions.

Conclusions/Significance

In addition to regional cortical dysfunction, as indicated by abnormal alpha oscillations, there are patterns of functional network disruption affecting theta and alpha bands in AD that associate with the level of cognitive disturbance or with the APOE genotype. These functional patterns of nonlinear connectivity may potentially represent neurophysiological or phenotypic markers of AD, and aid in early detection of the disorder.