Investigation of association of 13 polymorphisms in eight genes in southeastern African American Alzheimer disease patients as compared to age‐matched controls

Alzheimer disease (AD) is an emotionally devastating and exceptionally costly disease. Apolipoprotein E (APOE) is a major risk factor gene for AD regardless of age of onset or family history. However, this association may not be as strong or consistent in ethnic groups such as African Americans, raising the possibility of other modifier gene(s). In a group of African American AD patients, a significantly increased risk of AD was associated with two E4 alleles (OR = 5.6; 95% CI = 1.5–21.0) or one E4 allele (OR = 2.5; 95% CI = 1.3–5.0) when compared to E3/E3 genotype, and there was a significant lowering of age of onset for affecteds with E4/E4 genotype as compared to one E2 allele (P = 0.02) or all others (P = 0.03). We also found a significant increase in age of onset with the ?308 #2 (A) allele of TNF when compared to AD cases with no #2 allele. A significant increase in age was also demonstrated with the #2 allele (99 base pairs) of the microsatellite TNFa, located ～ 10.5 kb upstream of TNF. When these two alleles were combined with the TNF ?238G (#1) allele to give a haplotype, the significant increase in age was still demonstrated. Polymorphisms in the APOE promoter and six other candidate genes did not appear to demonstrate any significant association with our African American AD patients. Our results confirm the established association of APOE4 to AD observed in several ethnic groups, including African Americans. In addition, TNF appears to have some modifying effect in AD, primarily on age of onset, or it could be in linkage disequilibrium with a modifier locus nearby. © 2001 Wiley‐Liss, Inc.     

Common variation in GRB-associated Binding Protein 2 (GAB2) and increased risk for Alzheimer dementia

GRB-associated binding protein 2 (GAB2) was recently reported to be a modifier of late-onset Alzheimer dementia (AD) risk in carriers of the APOE epsilon4 allele in a genome-wide association analysis. We aimed to investigate this association in a well-characterized Belgian late-onset AD patient/control group: 528 Belgian AD patients (mean onset age 79.0+/-5.2 years, 70.2% females) and 601 ethnically matched control individuals (mean age 61.9+/-15.3 years, 57.1% females) were genotyped for 10 SNPs across the GAB2 locus. For 2 SNPs the most common genotype was associated with risk for AD, with the most significant result for rs4945261 [OR 1.49 (95%CI 1.04-2.15)]. After stratification by presence or absence of APOE epsilon4 these associations were present in APOE epsilon4 carriers only. When assessing the effect of APOE and rs4945261 in one model, rs4945261 did not show a main effect, but the joint risk effect of rs4945261-GG and APOE epsilon4 on AD was significant (OR 3.87, 95%CI 2.66-5.63; p=1.0E-12), with a deviation of 1.87 from the multiplicative model of interaction. Haplotype analyses showed evidence of association in the total (global p(sim) 0.04) and APOE epsilon4+ (global p(sim) 0.02) but not in the APOE epsilon4 - group (global p(sim) 0.6). The association was driven by a higher frequency of the major haplotype in patients. Our data independently replicate an association between GAB2 and late-onset AD, which appears to be limited to APOE epsilon4 carriers.     

Apolipoprotein E (APOE) allele distribution in the world. Is APOE*4 a ‘thrifty’ allele?

Apolipoprotein E (APOE = gene, apoE = protein) plays a central role in plasma lipoprotein metabolism and in lipid transport within tissues. The APOE shows a genetic polymorphism determined by three common alleles, APOE * 2 , APOE * 3 , APOE * 4 and the product of the three alleles differs in several functional properties. APOE is involved in the development of certain pathological conditions. In particular, the APOE * 4 allele is a risk factor for susceptibility to coronary artery disease (CAD) and Alzheimer's Disease (AD). In the present study we analyzed the APOE allele distribution in the world. The APOE * 3 is the most frequent in all the human groups, especially in populations with a long-established agricultural economy like those of the Mediterranean basin (0.849–0.898). The frequency of APOE * 4 , the ancestral allele, remains higher in populations like Pygmies (0.407) and Khoi San (0.370), aborigines of Malaysia (0.240) and Australia (0.260), Papuans (0.368), some Native Americans (0.280), and Lapps (0.310) where an economy of foraging still exists, or food supply is (or was until the recent past) scarce and sporadically available. The APOE * 2 frequency fluctuates with no apparent trend (0.145–0.02) and is absent in Native Americans. We suggest that the APOE * 4 , based on some functional properties it has and on its distribution among human populations, could be identified as a 'thrifty' allele. The exposure of APOE * 4 to the contemporary environmental conditions (Western diet, longer lifespans) could have rendered it a susceptibility allele for CAD and AD. The absence of the association of APOE * 4 with CAD and AD in Sub-Saharan Africans, and its presence in African Americans, seems to confirm this hypothesis.     

Association of RFC1 A80G and MTHFR C677T polymorphisms with Alzheimer's disease

We examined polymorphisms in reduced folate carrier gene (RFC1) and methylenetetrahydrofolate reductase gene (MTHFR) for association with sporadic AD (SAD) in Chinese population. Significant associations of RFC1 A80G G allele and GG genotype with SAD (p=0.008, OR=1.312, 95%CI=1.072-1.605, and p=0.042, OR=1.383, 95%CI=1.012-1.890) were found. Further stratification of total samples by APOE epsilon4 carrier status, age/age at onset and gender revealed that RFC1 A80G G allele was an APOE epsilon4-independent risk factor for late-onset AD, and it might increase the risk of AD in females. No significant associations of MTHFR C677T allele and genotype with AD were observed in total samples, but significant associations of T allele and TT genotype with AD (p=0.031, OR=1.586, 95%CI=1.042-2.414, and p=0.028, OR=2.250, 95%CI=1.074-4.712) were identified in APOE epsilon4 carrier subgroup, suggesting that MTHFR 677 T allele and APOE epsilon4 allele may synergistically act to increase AD risk. No significant effect of RFC1 G80A and MTHFR C677T polymorphisms on plasma folate and homocysteine levels was detected.     

Butyrylcholinesterase K variant is genetically associated with late onset Alzheimer's disease in Northern Ireland

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that has been associated, sometimes controversially, with polymorphisms in a number of genes. Recently the butyrylcholinesterase K variant (BCHE K) allele has been shown to act in synergy with the apolipoprotein E epsilon4 (APOE epsilon4) allele to promote risk for AD. Most subsequent replicative studies have been unable to confirm these findings. We have conducted a case-control association study using a clinically well defined group of late onset AD patients (n=175) and age and sex matched control subjects (n=187) from the relatively genetically homogeneous Northern Ireland population to test this association. The BCHE genotypes of patients were found to be significantly different from controls (chi(2)=23.68, df=2, p<0.001). The frequency of the K variant allele was also found to differ significantly in cases compared to controls (chi(2)=16.39, df=1, p<0.001) leading to an increased risk of AD in subjects with this allele (OR=3.50, 95% CI 2. 20-6.07). This risk increased in subjects 75 years and older (OR=5. 50, 95% CI 2.56-11.87). At the same time the APOE epsilon4 associated risk was found to decrease from 6.70 (95% CI 2.40-19.04) in 65-74 year olds to 3.05 (95% CI 1.34-6.95) in those subjects 75 years and older. However, we detected no evidence of synergy between BCHE K and APOE epsilon4. The results from this study suggest that possession of the BCHE K allele constitutes a significant risk for AD in the Northern Ireland population and, furthermore, this risk increases with increasing age.     

HFE variants, APOE and Alzheimer's disease: findings from the population-based Rotterdam study

Iron is a reactive oxygen species and has been implicated in the pathogenesis of Alzheimer's disease (AD). In a population-based cohort study, including 268 incident AD patients and 2079 control individuals, we investigated the influence of the HFE C282Y and H63D variants and the apolipoprotein E4 (APOE epsilon 4) allele on the incidence, and age at onset of AD. There was no significant difference in the frequency of HFE variants in AD patients compared to controls. There was no significant effect modification by the APOE epsilon 4 allele. The mean age at onset was earlier in H63D homozygotes compared to non-carriers of this variant, in men (76.9+/-3.2 compared to 82.2+/-1.7) and women (82.1+/-3.9 compared to 84.5+/-1.7). In addition, in APOE epsilon 4 carriers, the mean age at onset of AD was earlier in men homozygous for the H63D variant (73.2+/-2.1 versus 78.7+/-1.6, p=0.05). Our results suggest that HFE variants are not strong determinants of AD in the general population but may modify the age of onset.     

The role of TNF and its receptors in Alzheimer’s disease

Tumor necrosis factor (TNF) is an important proinflammatory cytokine that is upregulated in Alzheimer disease (AD) patients and involved with AD genes. Several TNF promoter polymorphisms that increase expression are associated with inflammatory and infectious diseases. We previously reported results that detected a AD associated region near the TNF gene. Using family-based association tests we also reported an association between AD and a TNF haplotype in sibling-pair families, and a significant increase in the mean age of onset for a group of African-American AD patients carrying this same haplotype. Previous reports have shown that that the chromosome 1p and chromosome 12p regions are linked to late-onset AD. These two regions harbor TNF receptors (TNFR) 2 and 1, respectively, and binding to them mediates biological effects of TNF. We found a significant asssociation of a TNFR2 exon 6 polymorphism with late-onset AD in families with no individuals possessing the APOE E4E4 genotype under a dominant model. We found no significant association of three polymorphisms in the TNFR1 gene to AD. These results provide further evidence for the involvement of TNF in the pathogenesis of AD.     

Tumor necrosis factor-alpha -308A/G polymorphism is associated with age at onset of Alzheimer's disease

Pro-inflammatory cytokines and acute-phase proteins play an important role in Alzheimer's disease (AD) neurodegeneration, and common polymorphisms of genes controlling their production have been shown to be associated with AD. Tumor necrosis factor (TNF)-alpha is an inflammatory cytokine involved in the local immune response occurring in the central nervous system of AD patients. Genetic variation could contribute to the risk of developing AD or influence the age at the onset of the disease. We genotyped 222 patients (152 women, 70 men; age range 60-87) and 240 non-demented age-matched healthy controls for TNF-alpha -308 G/A single nucleotide polymorphism (SNP). No significant differences were observed in genotyped frequencies between patients and controls, whereas carriers of -308A showed a significantly lower mean age at onset than non-carriers of this allele. This difference was more evident taking into account ApolipoproteinE (ApoE) status since the lowest age at onset was observed in patients carrying the -308ATNF+/APOE4+ genotypes. In conclusion, our data support previous suggestions that, at least in Caucasians, the TNF gene is a disease modifier gene in patients in which AD is rising, bringing to light the importance of genetic variation at the pro-inflammatory components in the progression of AD.     

Apolipoprotein E and α-1-antichymotrypsin allele polymorphism in sporadic and familial Alzheimer's disease

Alzheimer disease (AD) patients with both sporadic and familial forms of AD and non-demented controls were genotyped for common polymorphisms in the signal peptide for α-1-antichymotrypsin (ACT) gene and in two different regions of apolipoprotein E (APOE) gene. The ACT TT genotype was over-represented (P=0.025) in patients with early onset of sporadic AD. In this patient's group ACT TT genotype conferred a significant crude odds ratio for the disease (OR=2.09; 95% CI=1.09–4.00, P=0.025). After adjustment for the APOE ε4 and APOE −491 genotypes, logistic regression analysis confirmed that the ACT TT genotype resulted independently associated with early onset AD (adjusted OR=2.56; 85% C.I.=1.3–5.2, P=0.009). The frequency of APOE ε4 allele was increased in AD, as expected (OR=5.92, 95% CI=3.60–9.70, P=0.0001). On the contrary, the APOE −491 A/T genotypes were not associated with AD. No preferential association of the APOE ε4 allele or APOE −491 A/T genotypes with ACT A/T alleles was observed in AD. Present findings indicated that subjects with ACT TT genotype had an increased risk of developing AD and suggested that this genotype influenced the risk of an early onset of the disease by affecting the production of ACT molecules.     

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.     

Apolipoprotein E type ε4 allele, heritability and age at onset in twins with Alzheimer disease and vascular dementia

The apolipoprotein E (APOE) ε4 allele is a risk factor in Alzheimer disease (AD), but not in vascular dementia (VaD). We have investigated whether the ε4 allele is more common in twin pairs concordant for AD, compared with those discordant for AD, and whether the ε4 allele is more common in AD twins than in VaD twins. In addition, we have investigated the relationship of the ε4 allele and the age at onset in AD and VaD. APOE genotype was analysed in 29 senile demented twin pairs. The ε4 allele was associated with AD and not with VaD. However, there was no difference in the frequency of the APOE ε4 allele in concordant (33.3%) and discordant (31.3%) AD dizygotic twin pairs. Age at onset in AD was significantly lower in ε4 homozygotes than in individuals with one or no copies of ε4 (62.4 vs. 73.5, p < 0.01). In concordant AD twin pairs, the ε4 allele frequency was somewhat higher in the twins with earlier onset (41.7% vs. 25%), but the difference was not statistically significant. In the VaD group the age at onset was not significantly different between individuals with or without ε4 in their genotypes.     

Association between apolipoprotein E polymorphism and serum lipid and apolipoprotein levels with Alzheimer's disease

We have recently demonstrated that apolipoprotein E (APOE)-varepsilon4 allele is a risk factor for Alzheimer disease (AD) in Tehran, Iran. The current study specifically aimed to examine whether APOE polymorphism in association with serum lipids-apolipoprotein level is a risk factor for AD in a population from Tehran, Iran. APOE polymorphism and plasma lipids, apoA1, apoB and lipoprotein (a) (Lp(a)) levels were determined in 94 AD patients and 111matched controls. Our study demonstrated a significant association between APOE polymorphism and the level of plasma lipids and apolipoprotein with AD in this population. The AD subjects had significantly lower apoA1 (p<0.001) and HDL-C (p<0.01) and higher apoB (p=0.01) and LDL-C (p=0.02) levels than that of the control group. The AD subjects carrying APOE-varepsilon4 allele had lower plasma apoA1 (t=5.2, p<0.002) and HDL-C level (t=2.7, p=0.01) but had higher plasma apoB (t=-5.4, p<0.002), LDL-C (t=-4.6, p=0.005) and total cholesterol (TC) (t=-2.7, p=0.01) than that of the non APOE-varepsilon4 carriers. These results indicated that AD patients with APOE-varepsilon4 allele has a distinct plasma lipid profile and carrier of this allele with low levels of apoA1 and HDL-C may be more susceptible to AD.     

Risk of late-onset Alzheimer's disease associated with BDNF C270T polymorphism

We examined the frequency of the T allele of the C270T polymorphism of the brain-derived nerve growth factor (BDNF) gene in a test and replication test design. Our objective was to determine if there is an association between the BDNF gene and Alzheimer's Disease (AD) in a US population. There were 106 autopsy-proven AD cases and 101 controls of similar ages in each test for a total of 212 AD cases and 202 controls. We found that there was a significant increase in the T allele in both the initial set (p=.04) and in the replication set (p=.018). For both groups combined p=.0008. Odds ratio=3.28, 95% CI=1.69-6.34. There were 54 cases of early-onset AD (EOAD) and 159 cases of late-onset AD (LOAD). The results were only significant for LOAD, p=.0002, odds ratio=3.81, 95% CI=1.93-7.52. The r2 or fraction of the variance attributed to the BDNF gene for the LOAD cases was .046. The results were independent of the APOE epsilon4 allele. When the younger controls were removed, providing a close age match to the AD subjects, the frequency of the T allele was even lower and the differences were still significant for both total AD and LOAD cases. In a logistic regression analysis including APOE, age, sex and BDNF, BDNF was significant at p<.0001. We concluded that BDNF gene variants are significant risk factors for late onset AD.     

TNF polymorphisms in Alzheimer disease and functional implications on CSF beta-amyloid levels

Alzheimer disease (AD), vascular dementia, and stroke are all associated with inflammation though their respective initiating factors differ. Recently a polymorphism in the proinflammatory cytokine tumor necrosis factor (TNF), in association with apolipoprotein E (APOE), was reported to increase AD risk. Two SNPs, rs1799724 (-850C>T; NT_007592.14:g.22400733C>T) and rs1800629 (-308G>A; [NT_007592.14:g.22401282G>A]), and the APOE polymorphism were genotyped in 506 patients with sporadic AD and in 277 cognitively healthy controls. In a subset of 90 individuals we also investigated whether these SNPs exerted any functional effects on cerebrospinal fluid (CSF) beta-amyloid (Abeta) levels. The frequency of the rs1799724 genotypes and the rs1799724-T allele were significantly different in AD individuals (P=0.009; odds ratio [OR], 1.63; 95% confidence interval [CI], 1.13-2.34), while the rs1800629 SNP was not associated with AD. Significant interaction was observed between the rs1799724-T and APOE epsilon4 alleles in that the rs1799724-T allele significantly modified risk associated with possession of the epsilon4 allele only (epsilon4 in absence of rs1799724-T: OR, 2.92; 95% CI, 2.00-4.27; epsilon4 in presence of rs1799724-T: OR, 6.65; 95% CI, 3.26-13.55; P=0.03). Haplotyping analysis revealed a significant overrepresentation of an rs1799724-T/rs1800629-G haplotype in AD (P=0.012; OR, 1.60; 95% CI, 1.11-2.29), although to a lesser degree than rs1799724-T alone. Further, the rs1799724-T allele was found to be associated with lower levels of CSF Abeta42 (P=0.023), thus corroborating the genetic findings. Inheritance of the rs1799724-T allele appears to synergistically increase the risk of AD in APOEepsilon4 carriers and is associated with altered CSF Abeta42 levels. Further investigations are warranted to assess the significance of these novel findings.     

Low density lipoprotein receptor-related protein gene polymorphisms and risk for late-onset Alzheimer's disease in a Japanese population

Low density lipoprotein (LDL) receptor-related protein (LRP) gene polymorphisms located in the 5' region and in exon 3, and the apolipoprotein E (APOE) genotype were determined in 100 Japanese patients affected by late-onset Alzheimer's disease (AD). We matched 246 controls for age and found no association between the polymorphism located in the 5' region of the LRP gene. The distribution of LRP exon 3 genotypes and alleles did not differ between AD and the control groups. However, the frequency of T allele in the Alzheimer's group having APOE-epsilon4 was lower than that in the control group having APOE-epsilon4, but it was only marginally significant (p = 0.022). Age of onset was significantly younger in the patients with CC genotype than those carrying the T allele (p = 0.03), and this trend was more evident among non-APOE-epsilon4 carriers (p = 0.008). These results support the possibility that ApoE and LRP may contribute to the development of AD.     

No association between the intronic presenilin 1 polymorphism and Alzheimer's disease in the Chinese population

Wragg et al. [1996: Lancet 347:509-512] recorded an association between the intron-based presenilin 1 (PS1) genotype 1/1 and late-onset Alzheimer's disease (AD). This study was performed to determine if there is a similar association in the Chinese population. Ninety-one AD cases, 50 multiinfarct dementia (MID) patients, and 73 age-matched normal controls were recruited. Genotyping of PS1 and apolipoprotein E (APOE) was performed by the methods of polymerase chain reaction and restriction fragment length polymorphism. In AD, MID, and normal controls PS1 allele 1 frequency was 0.6703, 0.5600, and 0.6301, respectively; PS1 allele 2 frequency was 0.3297, 0.4400, and 0.3699, respectively. No association was detected between these diseases and any PS1 allele or genotype. There was only a nearly significant negative association between MID and PS1 genotype 1/1 in the subgroup population bearing APOE allele E4 (odds ratio = 0.2753, P = 0.0776). Our results do not support the conclusion that the intronic PS1 polymorphism is associated with Alzheimer's disease.     

Apolipoprotein E epsilon 4 affects new learning in cognitively normal individuals at risk for Alzheimer's disease

The Apolipoprotein E (APOE) epsilon 4 allele is an important risk factor for Alzheimer's disease (AD). Given the interest in early identification of at-risk individuals, we examined memory decline as a function of APOE status and age in cognitively intact participants aged 48-77 years old (yo). Participants were grouped by age (<60 versus > or =60) and APOE (epsilon4+/-). Longitudinal analysis of several components of memory over a 2-year interval showed a significant Age-by-APOE interaction reflecting a decline in new learning for the > or =60 epsilon4+ group only. Among epsilon4+, 76% of the > or =60 participants showed a decline versus 32% of the <60, but the amount of decline in new learning over the 2-year interval within the > or =60 group was not further influenced by age. That is, the size of the 2-year change was the same for 60 and 70 year old participants. This suggests that longitudinal study of new learning is a sensitive measure for detecting early cognitive changes in at-risk individuals that precede the symptomatic onset of mild cognitive impairment and AD.     

Activation of gonadotropin-releasing hormone receptors induces a long-term enhancement of excitatory postsynaptic currents mediated by ionotropic glutamate receptors in the rat hippocampus

Besides apolipoprotein E (APOE) polymorphism, whose association with Alzheimer's disease (AD) has been confirmed in most of the numerous population samples studied, other markers have been investigated. In most cases the association firstly described was not confirmed in subsequent works. Since it is important to examine these associations in as many populations as possible, we investigated APOE, APOC1, APOC2, alpha-1 antichymotrypsin (ACT) and presenilin-1 (PS-1) polymorphisms in a series of elderly patients with late-onset sporadic AD from Northern Italy and in a sex and age-matched control group. We could not confirm the significantly higher frequency of the ACT*A allele among carriers of APOE e*4 allele described elsewhere, although a similar trend was observed. The APOC2 and the PS-1 distributions were similar between patients and controls. However, we observed a significant difference in the genotype and allele frequencies of APOE and APOC1: patients had higher e*4 and C1*2 allele frequencies. This finding confirms the important role for APOE in AD occurrence. In addition, APOC1 seems to be an interesting marker because, though in strict linkage disequilibrium with APOE, it seems to play an independent role in AD risk. In contrast to previously reported data, plasma apoE concentrations were similar in patients and in controls. An interaction between APOE and APOC1 polymorphisms and apoE levels was observed in patients: subjects carrying the APOE E3/E2 or the APOC1 2-2 genotype have higher apoE concentrations than those who do not.     

Allelic association but only weak evidence for linkage to the apolipoprotein E locus in late-onset Swedish Alzheimer families

An association between the ϵ4 allele of the apolipoprotein E gene (APOE) and late-onset Alzheimer's disease (AD) was recently demonstrated. In order to confirm the association and to gauge the ability of standard genetic linkage methods to identify susceptibility genes, we investigated 15 Swedish late-onset AD families. We found an association of familial AD to the APOE ϵ4 allele (P = 0.01) but no indication of linkage to the APOE region using 2-point linkage analysis, and only weak evidence using the affected pedigree-member (APM) method. Our results confirm an APOE ϵ4 association with late-onset familial AD and indicate that susceptibility genes can easily be missed when using standard lod score and APM genetic linkage analysis. © 1996 Wiley-Liss, Inc.