Association between promoter polymorphisms in anterior pharynx-defective-1a and sporadic Alzheimer's disease in the North Chinese Han population

Amyloid β-peptide (Aβ) deposition in brain is important in the development of sporadic Alzheimer's disease (SAD) and Aβ is produced through sequential cleaving of amyloid precursor protein (APP) by β-secretase and γ-secrease. Anterior pharynx-defective-1 (APH-1) is an important subunit of the gamma-secretase complex, and its expression level was associated with the activity of γ-secrease. We hypothesized that alterations in the APH-1 promoter region might alter APH-1 expression and the activity of γ-secrease, thus be involved in the SAD process. In the present study, we sequenced APH-1a promoter region in 20 randomly selected controls and 20 SAD patients and detected two polymorphisms which were −980C/G (rs3754048) and −21C/A (rs2275780). Then, we investigated genotypes and allele of these two polymorphisms as well as apolipoprotein ?4 (APOE ?4) status in 256 SAD patients and 276 normal controls with restriction fragment length polymorphisms analysis and sequencing. Results showed the GG genotype and G allele of −980C/G polymorphism were more frequent in the SAD group than that in the controls not only in the whole subjects (genotype P = 0.038, allele P = 0.01 respectively) but also in the APOE ?4 + subjects (genotype P = 0.048, allele P = 0.016 respectively). There was no statistical difference between SAD group and controls regarding to the frequency of alleles and genotypes of −21C/A whenever before or after stratification by APOE ?4. Our results suggest that there is an association between −980C/G and the development of SAD in the Northern Han Chinese population and that allele G may interact synergistically with the APOE ?4 allele to increase the risk of SAD.     

Association between neprilysin polymorphisms and sporadic Alzheimer's disease

The deposition of amyloid beta peptide (Abeta) in the form of plaques in the brain is a hallmark of Alzheimer's disease (AD). Neprilysin is the major Abeta-degradating enzyme and reduction in neprilysin activity could contribute to Alzheimer's by increasing the steady-state level of Abeta. To provide further evidence for the role of neprilysin in AD we genotyped 22 polymorphisms, 21 SNPs and the GT repeat in the promoter region, across the neprilysin gene in 298 Caucasian sporadic Alzheimer's patients and 298 age-matched controls. Several SNPs showed genotypic and allelic association to AD. SNP rs1836915, in linkage disequilibrium block 2, showed the greatest extent of genotypic association with AD (p=0.0076). We were unable to replicate any of the SNPs that were previously reported as putatively associated with AD. However, these novel findings add to the weight of evidence supporting the involvement of neprilysin in the aetiology of Alzheimer's disease.     

Genetic association between low-density lipoprotein receptor-related protein gene polymorphisms and Alzheimer's disease in Chinese Han population

Alzheimer's disease (AD) is the most common neurodegenerative disorders in the elderly. Low-density lipoprotein receptor-related protein (LRP), as a receptor of apolipoprotein E (APOE), APP, and alpha2 macroglobulin (alpha2-M), keeps the balance between degeneration and production of beta-amyloid protein (Abeta) clearance. Its gene had been defined as a candidate gene for AD, but the results were not universal. Total 496 AD patients and 478 controls were recruited in Chinese Han population and real-time PCR was used to detect the polymorphism of LRP C766T. Multiple logistic regression, Chi-square test and survival analysis were performed to explore the association. The distribution of LRP genotypes and alleles was significantly different between cases and controls, and T allele could reduce the risk for developing AD (OR of CT genotype: 0.57; 95% CI: 0.38-0.85, rho=0.003; OR of T allele: 0.57; 95% CI: 0.39-0.83, rho=0.003). TT genotype carriers had 5 years later for developing AD compared with CC genotype carriers, but survival analysis did not conform this (LRP TT vs. CT and CC log rank chi(2)=2.71, rho=0.26). The distribution of LRP C766T genotypes and alleles was different among different severity stratified by MMSE yet (rho=0.26). Our data suggested that the polymorphism of LRP C766T was strongly associated with AD and T allele might be a protective factor for AD in Chinese Han population.     

Association between promoter polymorphisms of the nicastrin gene and sporadic Alzheimer's disease in North Chinese Han population

Increasing evidences have shown that nicastrin (NCSTN) plays a crucial role in γ-cleavage of the amyloid precursor protein (APP). Inhibition of NCSTN demonstrated an altered γ-cleavage activity, suggesting its potential implication in developing Alzheimer's disease (AD). We detected the NCSTN gene promoter region in 359 sporadic AD (SAD) patients and 331 controls and found three promoter single nucleotide polymorphisms (SNPs): −1216C/A (rs2147471), −796T/G (rs10752637) and −436C/T (rs1324738). For −1216C/A, there were significant differences in the allele and genotype frequency between AD and control subjects (allele P = 0.031, genotype P = 0.017). The allele and genotype frequencies remained significant before and after APOE?4 stratification. The −1216CC carriers increased 2-fold risk for the development of SAD compared to the carriers with −1216CA and AA genotypes (OR = 2.049, 95%CI = 1.410–2.976, P = 0.000). For −796T/G, there were significant differences in the genotype frequency between SAD and control subjects (P = 0.009). This trend is still obvious in the subjects without APOE?4 allele. The −796GG carriers might decrease the risk compared to the carriers with −796TG and TT genotypes (OR = 0.602, 95%CI = 0.393–0.932, P = 0.022). No significant difference was detected either in genotype or in allele frequencies between SAD and control for −436C/T, even after APOE?4 stratification. The haplotype −1216A/−796G may be a protective factor for SAD (OR = 0.795, 95%CI = 0.636–0.995, P = 0.045). Our investigation suggests that −1216C/A and −796T/G are probably related to the development of SAD.     

Association between promoter polymorphisms of vascular endothelial growth factor gene and sporadic Alzheimer's disease among Northern Chinese Han

Increasing evidences suggest that polymorphisms within the promoter region of the vascular endothelial growth factor (VEGF) gene may elevate the risk for Alzheimer's disease (AD). In Northern Chinese Han, we found three polymorphisms in the VEGF promoter: −2578C/A (rs699947), −2549I/D (rs35569394) and −1154G/A (rs1570360). A strong linkage disequilibrium was detected between −2578C/A and −2549I/D. After adjusting the data by gender, age and the APOE?4 status using logistic regression, the −1154G/G genotype was found to increase the risk for sporadic AD (SAD) by 1.4-folds. In the subgroup of APOE?4 non-carriers, the −1154G allele and −2549D/−1154G haplotype were observed to be significantly higher in the 279 SAD patients than in the 317 healthy individuals. The present study provides the evidence that the −1154G allele and the −2549D/−1154G haplotype may be associated with the development of SAD in the individuals without APOE?4 allele.     

CSF somatostatin in Alzheimer's disease

Studies have previously demonstrated low somatostatin levels in autopsy cortical tissue from Alzheimer's disease (AD) patients and low somatostatin levels in CSF obtained from subjects with dementia. We evaluated levels of this peptide in 21 non-depressed subjects, 10 with AD, 2 with Parkinson's disease (PD), and 9 with other neurological conditions. The AD patients had significantly lower mean CSF somatostatin than the "other" neurological patients (14.6 +/- 1.5 S.E.M. versus 26.7 +/- 3.2 pg/ml, p less than 0.005). A demented PD subject had a level in the range of the AD group, while the non-demented PD patient had a value above this range. Thus, all 11 patients with AD or PD dementia, analogous disorders, had levels below 21.8 mg/ml, while 7 of the 10 remaining patients had values above 21.8 pg/ml. Age did not explain this finding.     

Association between late-onset Alzheimer's disease and microsatellite polymorphisms in intron II of the human toll-like receptor 2 gene

The amyloid beta protein (Aβ) deposits in the brains of patients with Alzheimer's disease (AD) are closely associated with innate immune responses that were assumed to play a pivotal role in the pathogenesis of AD. Toll-like receptor 2 (TLR2) is thought to contribute to Aβ clearance. Studies have reported the presence and functional implications of guanine-thymine (GT) repeat microsatellite polymorphisms in intron II of the human TLR2 gene. The present study evaluated the association of the microsatellite polymorphism and sporadic late-onset AD (LOAD) in the Han Chinese population. The numbers of (GT) repeats were counted in 137 AD patients and in 137 non-AD control subjects, using polymerase chain reaction and genescan analysis. The alleles were divided into three subclasses: (GT)16 or less as the S allele, (GT)17 to (GT)22 as the M allele, and (GT)23 or more as the L allele. Patients with AD had more S alleles (P < 0.001; odds ratio (OR) = 2.32; 95% confidence interval (CI) = 1.57–3.42) and fewer L alleles (P = 0.02; OR = 0.66; 95% CI = 0.46–0.93) than did healthy controls. Genotypes SS and SM were more common, whereas ML and SL were less common in patients with AD. In subgroup analyses, the genotypes including S alleles were associated with an increased risk of LOAD (OR = 2.05, 95% CI = 1.26–3.34), and this association was influenced by the presence of APOE ?4 alleles. This study demonstrates an association of microsatellite polymorphisms in intron II of the human TLR2 gene with risk for LOAD in Han Chinese.     

Association between the macrophage inflammatory protein-l alpha gene polymorphism and Alzheimer's disease in the Chinese population

Genetic polymorphisms in chemokine receptor and their natural ligand genes have been shown to modify the disease progression of Alzheimer's disease (AD). Human macrophage inflammatory protein-1 alpha (MIP-1alpha) is a chemotactic cytokine which plays a considerable role in AD pathogenesis, but its genetic contribution to AD has never been investigated. Recently, a biallelic dinucleotide microsatellite repeat (TA repeat) polymorphism has been found in the MIP-1alpha gene promoter region at position -906. We investigated whether this promoter polymorphism of MIP-1alpha gene might be responsible for susceptibility to AD in a Chinese population, utilizing a clinically well-defined group of 138 sporadic AD patients and 180 age-matched controls. We also examined the combined gene effects between the MIP-1alpha and apolipoprotein E (APOE) genes. The overall distribution of MIP-1alpha-906 alleles and genotypes was significantly different between AD cases and controls (P<0.05). The odds ratio for AD associated with the (TA)(6)/(TA)(6) versus non-(TA)(6)/(TA)(6) genotype was 1.893 (95% CI=1.208-2.967), while that for APOE varepsilon4 and MIP-1alpha (TA)(6)/(TA)(6) carriers was 7.140 (95% CI=3.222-15.823). In addition, we found that serum MIP-1alpha levels in patients with (TA)(6)/(TA)(6) genotype were increased significantly when compared with non-(TA)(6)/(TA)(6) genotype. The results indicate that the MIP-1alpha-906 (TA)(6)/(TA)(6) genotype, either by itself or interacting with the APOE varepsilon4 gene seems to be a genetic risk factor for AD. This genotype is associated with elevated serum MIP-1alpha levels in patients, which can contribute to increase the inflammatory process occurring in AD.     

Implication of IL-33 gene polymorphism in Chinese patients with Alzheimer's disease

Interleukin-33 (IL-33), a newly described member of the IL-1 family, is located on chromosome 9p24, a chromosomal region of interest in Alzheimer's disease (AD) defined by many genome-wide studies. Three intronic rs1157505, rs11792633, and rs7044343 single nucleotide polymorphisms (SNPs) within IL-33 have recently been reported to be associated with risk of AD in Caucasian populations. In order to assess the involvement of the IL-33 polymorphisms in the risk of developing late onset AD (LOAD), we analyzed the genotype and allele distributions of these 3 polymorphisms in 704 Han Chinese subjects. The minor alleles of the rs11792633 polymorphism within IL-33 was significantly associated with a reduced risk of LOAD (odds ratio [OR] = 0.73, p = 0.005). Furthermore, rs11792633 polymorphism was still strongly associated with LOAD (dominant model: OR = 0.67, p = 0.015; recessive model: OR 0.57, p = 0.021; additive model: OR = 0.71, p = 0.004) after adjusting for age, gender, and the apolipoprotein E (APOE) ε4 status. Our results support the evidence that genetic variants of IL-33 affect susceptibility to LOAD in Han Chinese.     

Association study between two novel single nucleotide polymorphisms and sporadic Parkinson's disease in Chinese Han population

Two novel single nucleotide polymorphisms (SNPs) (rs6812193 and rs11868035) were recently identified to be associated with Parkinson's disease (PD) in a Web Based Genome-Wide Association Study. Herein, we conducted a case–control study to evaluate the possible associations between these two SNPs and PD in Chinese Han population. All subjects (501 sporadic PD patients and 502 normal controls) were genotyped using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis with these two SNPs. Chi-square test revealed no significant difference in either genotype frequencies or allele frequencies, even after being stratified by age. But we found that the genotype and allele frequency of rs6812193 shows difference between male patients and male controls (p = 0.031, OR = 0.584; p = 0.037, OR = 0.606) but none in the female. Our findings suggest that rs11868035 may have no association with PD in Chinese population and rs6812193 may have marginal association with PD in male Chinese population. However, due to the limited data in the present study, replication studies in larger sample and other populations are required.     

Lack of an association between Paraoxonase 1 gene polymorphisms (Q192R, L55M) and Alzheimer's disease: a meta-analysis

The association between Paraoxonase 1 (PON1) gene polymorphisms (Q192R, L55M) and Alzheimer's disease (AD) risk has been reported inconsistent results. To assess the association between PON1 polymorphisms and AD risk, a meta-analysis was performed. Based on comprehensive searches of the PubMed, Embase, Web of Science, Weipu, and CBM databases, a total of 10 studies including 3081 AD cases and 3054 controls were identified. The pooled odds ratio (OR) with 95% confidence interval (95% CI) were performed. There was no significant association between PON1 Q192R polymorphism and AD risk in all comparison models (R vs. Q, OR=0.89, 95% CI=0.82-0.96; RR vs. QQ, OR=0.83, 95% CI=0.68-1.01; RR+RQ vs. QQ, OR=0.86, 95% CI=0.75-0.97; and RR vs. QR+QQ, OR=0.94, 95% CI=0.81-1.11). For the PON1 L55M polymorphism, lack of an association was also found (L vs. M, OR=0.95, 95% CI=0.86-1.05; LL vs. MM, OR=0.67, 95% CI=0.51-0.88; LL vs. ML+MM, OR=0.82, 95% CI=0.69-0.98; and LL+ML vs. MM, OR=0.75, 95% CI=0.58-0.96). On subgroup analysis by ethnicity, similar results were found. Conclusively, the present meta-analysis revealed that PON1 gene polymorphisms (Q192R, L55M) were unlikely to contribute to AD susceptibility.     

Genetic variation in Clusterin gene and Alzheimer's disease risk in Han Chinese

Clusterin gene (CLU), also known as apolipoprotein J (ApoJ), is a strong candidate gene for late-onset Alzheimer's disease (LOAD) according to the Alzgene database. To further characterize this association and to isolate the variants contributing to the pathogenesis of LOAD in Han Chinese, we first sequenced a small sample (n = 100) to discover variants in the promoter, exons, the 5′ and 3′ untranslated regions, and exon–intron boundaries of CLU. Follow-up genotyping of identified variants in a larger sample (n = 1592). Sequencing analysis identified 18 variants. Analysis in the larger population revealed that only the rs9331949 C allele was significantly associated with an increased risk of LOAD, even after adjusting for multiple testing (p = 0.026). Logistic analysis identified the rs9331949 polymorphism was still strongly associated with LOAD (additive model: p = 0.004, odds ratio = 1.274; dominant model: p = 0.039, odds ratio = 1.239; recessive model: p = 0.002, OR = 1.975) after adjusting for sex, age, and APOE ε4 status. Our findings implicate CLU as a susceptibility gene for LOAD in Han Chinese.     

Association between haplotype −88G/25G in A2M with Alzheimer's disease

Alpha 2-Macroglobulin gene (A2M) has been recognized as a candidate gene for late-onset Alzheimer's disease (AD), but the association between several polymorphisms in A2M gene and risk for AD remained controversial. Moreover, little is known regarding the effects of polymorphisms in A2M promoter region on AD susceptibility. Our study aimed to detect polymorphisms in A2M promoter region, and then evaluate their relationship to sporadic AD (SAD). One single nucleotide polymorphism (−88A/G) in proximal promoter region was found by sequencing, and further analyzed with an established 25T/G polymorphism in 179 SAD patients and 179 age-gender-matched controls. Allele A in −88A/G polymorphism was more prevalent in cases, with a 1.7-folded risk for SAD (OR = 1.74, 95%CI 1.05–2.91, P = 0.031), while G allele in 25T/G was less prevalent in cases, with a 43% reduced risk for SAD (OR = 0.57, 95%CI 0.36–0.89, P = 0.013). After adjusted the effects of age, gender and APOE?4 allele status in logistic regression model, the protective effects of −88G and 25G on SAD still remained. Individuals who carried haplotype −88G/25G had a significant 44% reduced risk for SAD compared to those who did not carry (OR = 0.56, 95%CI 0.34–0.94, P = 0.027), while haplotype −88A/25T carriers had an increased risk for SAD compared to those who did not carry (OR = 1.77, 95%CI 1.06–2.96, P = 0.027). Our study supports that haplotype −88G/25G might play a protective role in the development of SAD, and the protective effects of −88G and 25G were independent of APOE?4 allele.     

Tau-tubulin kinase-1 gene variants are associated with Alzheimer's disease in Han Chinese

Tau-tubuline kinase 1 (TTBK1) is a recently discovered brain-specific protein kinase involved in tau phosphorylation at AD-related sites. A recent large study has identified significant association of two single nucleotide polymorphisms (SNPs) (rs2651206 and rs7764257) in the TTBK1 gene with late-onset Alzheimer's disease (LOAD) in Spanish. Here, we performed a case–control study to clarify whether the risk for LOAD might be influenced by these polymorphisms in a large Chinese cohort consisting of 400 patients and 388 healthy controls. The minor alleles of the rs2651206 polymorphism within TTBK1 was significantly associated with a reduced risk of LOAD (odds ratio/OR = 0.69, P = 0.011). Furthermore, rs2651206 polymorphism was still strongly associated with LOAD (OR = 0.72, P = 0.05) after adjusted for age, gender, and the apolipoprotein E (APOE) ?4 status. Haplotype analysis identified the TG haplotype, deriving from the two minor alleles, to decrease the risk of LOAD (OR = 0.78, P = 0.037). This study provides the evidence that variations in the TTBK1 gene may play an important role in the pathogenesis of sporadic LOAD in a Han Chinese population.     

Genetic variation in BIN1 gene and Alzheimer's disease risk in Han Chinese individuals

Genome-wide association studies have identified the bridging integrator 1 (BIN1) gene as the most important genetic susceptibility locus in late-onset Alzheimer's disease (LOAD) after apolipoprotein E for individuals of European ancestry. To further characterize this association and to isolate the variants within BIN1 contributing to LOAD in Han Chinese individuals, we conducted a 2-step design study in our cohort of 1133 LOAD patients and 1159 control subjects. Sequencing analysis identified 44 variants within BIN1. Follow-up genotyping analysis revealed that a novel missense mutation P318L appeared to exert risk effect for development of LOAD; and rs67327804 was also significantly associated with LOAD risk even after adjusting for age, gender, and apolipoprotein E ε4 status. Haplotype analysis confirmed that the “GA” haplotype derived from single-nucleotide polymorphisms in rs67327804 and rs1060743 showed a 1.4-fold increased risk of LOAD. Our findings provided the first independent evidence that variants in BIN1 were significantly associated with LOAD in Han Chinese individuals.     

Gliovascular alterations in sporadic and familial Alzheimer's disease: APOE3 Christchurch homozygote glioprotection

In response to brain insults, astrocytes become reactive, promoting protection and tissue repair. However, astroglial reactivity is typical of brain pathologies, including Alzheimer's disease (AD). Considering the heterogeneity of the reactive response, the role of astrocytes in the course of different forms of AD has been underestimated. Colombia has the largest human group known to have familial AD (FAD). This group carries the autosomal dominant and fully penetrant mutation E280A in PSEN1, which causes early-onset AD. Recently, our group identified an E280A carrier who did not develop FAD. The individual was homozygous for the Christchurch mutation R136S in APOE3 (APOEch). Remarkably, APOE is the main genetic risk factor for developing sporadic AD (SAD) and most of cerebral ApoE is produced by astroglia. Here, we characterized astrocyte properties related to reactivity, glutamate homeostasis, and structural integrity of the gliovascular unit (GVU), as factors that could underlie the pathogenesis or protection of AD. Specifically, through histological and 3D microscopy analyses of postmortem samples, we briefly describe the histopathology and cytoarchitecture of the frontal cortex of SAD, FAD, and APOEch, and demonstrate that, while astrodegeneration and vascular deterioration are prominent in SAD, FAD is characterized by hyperreactive-like glia, and APOEch displays the mildest astrocytic and vascular alterations despite having the highest burden of Aβ. Notably, astroglial, gliovascular, and vascular disturbances, as well as brain cell death, correlate with the specific astrocytic phenotypes identified in each condition. This study provides new insights into the potential relevance of the gliovasculature in the development and protection of AD. To our knowledge, this is the first study assessing the components of the GVU in human samples of SAD, FAD, and APOEch.     

Extremely rare incidence of the UBQLN1 polymorphism (UBQ-8i) in Taiwan Chinese with Alzheimer's disease

Recently, a single nucleotide polymorphism (SNP, A → G) in intron 8 of UBQLN 1 at the rs12344615 site (UBQ-8i) on chromosome 9q22 was associated with a higher risk of late-onset Alzheimer's disease (AD). Here, we aimed to investigate whether an association exists between the UBQ-8i polymorphism and AD in Taiwan Chinese. Initially, we included 100 late-onset AD patients and 100 gender- and age-matched non-demented (ND) control participants. The UBQ-8i polymorphism site was successfully determined in 91 AD and 96 ND individuals using the dye terminator nucleotide sequencing technique. Among the 187 participants, we did not detect any subject carrying the G allele. This finding is in agreement with the report listed in the NCBI SNP Reference Assembly, which states that <1% of Asians carry this SNP. The APOE ?4 allele, an established AD genetic risk factor, was overrepresented in the AD cohort. We conclude from these results that the UBQ-8i polymorphism of the UBQLN1 gene is extremely rare in Taiwan Chinese and unlikely to play a significant role in the risk of AD in Taiwan Chinese.     

Lack of association between rs597668 polymorphism near EXOC3L2 and late-onset Alzheimer's disease in Han Chinese

Recently, an international genome-wide association study (GWAS) additionally found rs597668 near EXOC3L2/BLOC1S3/MARK4 was a new genome-wide significance locus associated with late-onset Alzheimer's disease (LOAD) in Caucasians. Follow-up replication studies were conducted almost exclusively in Caucasians, and the effects of the risk locus in other populations are as yet unknown. This study investigated the GWAS-associated locus near EXOC3L2 in 1205 unrelated Northern Han Chinese subjects comprising 598 LOAD patients and 607 healthy controls matched for gender and age. The results showed no significant differences in the genotypic or allelic distributions of rs597668 polymorphism between LOAD cases and healthy controls (genotype: P = 0.653; allele: P = 0.603), even after stratification for apolipoprotein E (APOE) ?4 status and statistical adjustment for age, gender and APOE ?4 status. This study suggests that the rs597668 polymorphism near EXOC3L2 may not play a major role in the susceptibility to LOAD in the Northern Han Chinese population.     

Ubc9 gene polymorphisms and late-onset Alzheimer's disease in the Korean population: A genetic association study

Ubiquitin-conjugating enzyme E2I (Ubc9) ligates small ubiquitin-related modifier (SUMO) to target proteins, resulting in changes of their localization, activity, or stability. Sumoylation of amyloid precursor protein (APP) was reported to be associated with decreased levels of beta amyloid (Aβ) aggregates, suggesting that sumoylation may play a role in the pathogenesis of Alzheimer's disease (AD). We investigated the association between genetic variations of Ubc9 gene (UBE2I) and late-onset Alzheimer's disease (AD). Five single nucleotide polymorphisms (SNPs) in UBE2I were genotyped in the DNA samples of 312 AD patients, 347 subjects with mild cognitive impairment (MCI), and 489 cognitively healthy controls. The genotype distribution of a polymorphism in intron 7 (rs761059) differed between AD cases and controls, with an adjusted odds ratio (OR) of 1.45 (p = 0.046, 95% CI: 1.01–2.08). One haplotype (ht2 CAGAG) was found in 14.0% of the AD patients and in 11.1% of the controls (p = 0.04, OR = 1.43. 95% CI; 1.01–2.01). Stratification by the ApoE-?4 allele gave no significant difference between the groups. When the samples were stratified by gender, the genotypes of two SNPs (rs8052688, rs8063) were significantly associated with the risk of MCI among women. Our investigation suggests that UBE2I polymorphisms might be associated with a risk of AD and MCI.