Association of CLU and PICALM variants with Alzheimer's disease

Two recent large genome-wide association studies have reported significant associations in the CLU (APOJ), CR1, and PICALM genes with the risk of Alzheimer’s disease (AD). In order to replicate these findings, we examined 7 single nucleotide polymorphisms (SNPs) most significantly implicated by these studies in a large case-control sample comprising 2707 individuals. Principle components analysis revealed no population substructure in our sample. While no association was observed with CR1 SNPs (p = 0.30-0.457), a trend of association was seen with the PICALM (p = 0.071-0.086) and CLU (p = 0.148-0.258) SNPs. A meta-analysis of 3 studies revealed significant associations with all 3 genes. Our data from an independent and large case-control sample suggest that these gene regions should be followed up by comprehensive resequencing to find functional variants.     

Association analysis of the paraoxonase-1 gene with Alzheimer's disease

Genetic variants in the paraoxonase (PON) gene cluster, particularly a single C/T promoter polymorphism (rs 705381) in the PON-1 gene, have recently been associated with Alzheimer's disease (AD). The T allele, in particular, presents an increased risk for the development of AD. Here, we investigate the potential role of this polymorphism in an Italian case-control population consisting of 306 sporadic AD patients and 275 controls, and also evaluate a possible interaction with the ApoE genotype. No association between the PON-1 polymorphism and AD was observed. The T allele frequency was slightly over-represented in AD patients compared to the controls, but this was far from being statistically significant. Our sample was evaluated to have 97.3% power to detect an OR of 2.0 (64.3% power with OR = 1.5) at an α level of 0.05. No evidence of an interaction between the T risk-allele and the ApoE ?4 allele status and no effect of the PON-1 polymorphism on age at onset was detected. Our results do not support other studies indicating that the PON-1 promoter polymorphism plays a major role in AD, suggesting that other large studies are necessary to further elucidate the effect of PON on the development of the disease in the general population.     

Association study of the PIN1 gene with Alzheimer's disease

Genetic linkage studies indicate evidence for one or more Alzheimer's disease (AD) genes on chromosome 19 independently of the apolipoprotein E gene, a well-characterized AD-risk factor. Recently, the PIN1 gene on chromosome 19p13.2 has been proposed as a candidate gene for AD. Here, we have investigated the potential impact of two promoter polymorphisms (rs2233678 and rs2233679) within this gene on the risk of developing AD. No association of these polymorphisms or haplotypes with the disease was observed in a large French case-control population. Our data suggest that these genetic variants in PIN1 do not make a significant contribution to AD risk.     

Genetic association of CR1 with Alzheimer's disease: A tentative disease mechanism

CR1 is a novel Alzheimer's disease (AD) gene identified by genome-wide association studies (GWAS). Recently, we showed that AD risk could be explained by an 18-kilobase insertion responsible for the complement component (3b/4b) receptor 1 (CR1)-S isoform. We investigated the relevance of the CR1 isoforms to AD in a Canadian dataset. Also, we genotyped rs4844610 tagging the GWAS-significant CR1 single nucleotide polymorphisms. Individuals with F/S genotype had a 1.8 times increased risk for AD compared with F/F genotype (p-adjusted = 0.003), while rs4844610 was only marginally significant (p-adjusted = 0.024). The analyses of brain samples demonstrated that the CR1-S isoform is expressed at lower protein levels than CR1-F (p < 0.0001) hence likely associated with increased complement activation. Intriguingly, our neuropathological results show that the pattern of CR1 expression in neurons is different between the F/F and F/S genotypes (filiform vs. vesicular-like profiles). Furthermore, double labeling studies supported a differential distribution of CR1 in neurons (endoplasmic reticulum intermediate compartment vs. lysosomes). These observations indicate that the CR1-S and CR1-F isoforms could be processed in different ways in neurons. In conclusion, our results support that the CR1-S isoform explains the GWAS signals and open a novel prospect for the investigation of CR1-related disease mechanisms.     

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.     

No association between high temperature requirement 1 (HTRA1) gene polymorphisms and Alzheimer's disease

High temperature requirement 1 (HTRA1) gene is a plausible risk factor in Alzheimer's disease (AD) as it encodes a protease known to degrade amyloid-β peptide. Here we have studied whether single nucleotide polymorphisms (SNPs) in the HTRA1 gene or its nearby regions associated with AD in a large clinic-based case-control cohort originating from Finland. We did not observe significant association of the HTRA1 SNPs with AD among the whole case-control cohort or age-at-onset risk effect among AD patients.     

Association between genetic variants in sortilin-related receptor 1 (SORL1) and Alzheimer's disease in adults with Down syndrome

Recent reports have suggested that variants in the sortilin-related receptor gene (SORL1) increase the risk of late onset Alzheimer's disease (AD) in Northern European, Hispanic, African–American and Isreali–Arab populations. SORL1 directs trafficking of amyloid precursor protein (APP) and under-expression of SORL1 may lead to over-expression of β amyloid peptides. Adults with Down syndrome (DS) over-express APP and have early onset and high risk for AD. We investigated the relation of seven variants in the gene for SORL1 to age at onset and risk for AD among 208 adults with DS, 45–70 years of age at baseline. Participants were ascertained through the New York State developmental disability service system and followed at 18-month intervals. Information from cognitive assessments, caregiver interviews, medical record review and neurological examination was used to establish the diagnosis of dementia. Homozygosity for the minor T allele in rs556349 and for the minor C allele in rs536360 was associated with later age at onset and reduced risk of AD (HR = 0.26, 95% CI: 0.08–0.86; and HR = 0.40, 95% CI: 0.16–0.98, respectively). Mean age at onset was approximately four years later in individuals who were homozygous for those alleles compared with those who had at least one major allele. These findings indicate a modest association of variants in SORL1 with AD. In addition, we did not observe the same alleles to be associated with AD compared with earlier studies, suggesting that these SNPs are in linkage disequilibrium (LD) with the putative functional variants or that expression of the SORL1 gene and hence its interaction with APP might be modified by the extremely high levels of APP characteristic of Down syndrome. Thus, further studies are needed to identify functional variants that influence risk for AD in this uniquely vulnerable population.     

Association of TLR4 and TLR5 gene polymorphisms with Graves’ disease in Chinese Cantonese population

Graves’ disease (GD) is postulated to be caused by the combined effects of susceptibility genes and environmental triggers. Toll like receptors (TLRs) play a role in the activation of innate and adaptive immune responses in mammalians. The aim of this study was to evaluate the potential association of TLR4 and TLR5 gene polymorphisms with GD in Chinese Cantonese population. Four single nucleotide polymorphisms (SNPs), rs11536889 and rs7873784 in TLR4, rs2072493 and rs5744174 in TLR5, were evaluated in 332 GD patients and 351 unrelated controls from Chinese Cantonese population. The minor allele C of TLR5 rs5744174 decreased the risk to GD in females (OR_{C vs. T} = 0.63; p = 0.003; p_trend = 0.003). Under a dominant model, rs5744174 conferred a protective effect in all cases (OR_{CC/CT vs. TT} = 0.65; p = 0.009) or female subset (OR_{CC/CT vs. TT} = 0.57; p = 0.002). Under a co-dominant model, rs5744174 also conferred a protective effect in all cases (OR_{TC vs. TT} = 0.64; p = 0.008) and females (OR_{TC vs. TT} = 0.57; p = 0.002). The haplotype A-C of TLR5 (rs2072493–rs5744174) decreased the risk of GD in females (OR = 0.62; p = 0.002). The other three SNPs were not found associated with GD. This study provided evidence that polymorphisms in TLR5 might be associated with decreased susceptibility of GD in females.     

Investigation of TREM2, PLD3, and UNC5C variants in patients with Alzheimer's disease from mainland China

Recently, 3 rare coding variants significantly associated with Alzheimer's disease (AD) risk have been identified in western populations using whole exome sequencing method, including p.R47H in TREM2, p.V232M in PLD3, and p.T835M in UNC5C. To examine whether these variants are genetic risk factors in patients with AD from mainland China, we sequenced exon 2 of TREM2, exon 9 of PLD3, and exon 15 of UNC5C in Chinese Han population including 360 patients with AD and 400 control individuals. As a result, none of these 3 variants were identified in all subjects, however, 1 novel variant (p.A130V) in TREM2 and 4 novel variants (p.Q860H, p.T837K, p.S843G, and p.V836V) in UNC5C were detected in unrelated patients with late-onset AD. These findings suggest the 3 rare coding variants might not play an important role in AD risk in mainland China.     

Association between a variant of the sigma-1 receptor gene and Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with complex etiology and strong genetic predisposition. A number of investigations support the possible involvement of sigma non-opioid intracellular receptor 1 (SIGMAR1) in the pathophysiology of AD. We aimed to investigate the association between SIGMAR1 polymorphisms and late-onset AD, therefore we genotyped rs1799729 (GC-241-240TT) and rs1800866 (Q2P) in 322 Hungarian late-onset AD patients and 250 ethnically matched, elderly control individuals. The investigated polymorphisms were in nearly complete linkage disequilibrium resulting in the GC-Q and TT-P predominant haplotypes that were subjected to the statistical analyses. Our data demonstrates an association between the SIGMAR1 TT-P variant and the risk for developing AD (p=0.019), and a potential modest interaction effect (p=0.058) of the co-presence of the TT-P haplotype with apolipoprotein E4 allele on the risk for AD. Based on this mild significance, we could not fully support the hypothesis that TT-P haplotype in interaction with APOE E4 allele confers risk for developing AD.     

Association study of three polymorphisms of kinesin light-chain 1 gene with Alzheimer's disease

The transport of amyloid precursor protein is mediated through its interaction with kinesin light-chain 1 (KNS2). We hypothesized that kinesin light-chain dysfunction might be involved in the pathogenesis of Alzheimer's disease (AD). To assess the physiological relevance of an allelic variation in the KNS2 gene, the association analysis of three single nucleotide polymorphisms (SNPs) in the 5'UTR or in intronic sequences of KNS2 gene were performed in 100 AD brain patients and in 103 controls. For one of these polymorphisms (G58836C in intron 13), the association between AD and the C allele was found to be significant (odds ratio = 1.73, 95% CI: 1.12-2.67, P = 0.012). No synergistic effects were found between the APOE epsilon 4 allele and KNS2 gene polymorphisms.     

Association between the interleukin-1alpha gene and Alzheimer's disease: a meta-analysis

Inflammatory processes are involved in the pathogenesis of Alzheimer's disease (AD). Several studies have addressed the effects of interleukin-1 (IL-1) genes polymorphisms on the risk of developing AD. The results are not in full agreement on whether these polymorphisms are associated with the disease. To clarify this issue, we performed a meta-analysis of all the association studies between IL-1 genes and AD. Due to the relatively small number of published articles, the meta-analysis was restricted to the association of the IL-1alpha -889 C/T gene polymorphism and AD. Under a random effects model, the risk for the disease was significantly higher in subjects with the T/T genotype in comparison with both C/T (OR: 1.51; 95% C.I.: 1.15-1.99) and C/C (OR: 1.49; 95% C.I.: 1.09-2.03) subjects. There was modest heterogeneity for these effect estimates. Analysis of subgroups showed a significant association in patients with early-onset AD but not in late-onset AD. Our data support a significant but modest association between the T/T genotype of the IL-1alpha gene and AD.     

Genetic variation in GOLM1 and prefrontal cortical volume in Alzheimer's disease

Replications of the association between APOE-ε4 allele load and regional brain atrophy in Alzheimer's disease (AD) patients hold promise for future studies testing relationships between other disease risk gene variants and brain structure. A polymorphism, rs10868366, in the Golgi phosphoprotein 2 gene, GOLM1, was recently identified as an AD risk factor in a genome-wide association study. In a subset of the same AD cohort, we used voxel-based morphometry to test for association between the disease risk genotype and reduced regional gray matter (GM) volume in AD patients (n = 72). A mean 14% reduction in GM volume was observed in the left frontal gyrus with the higher risk GG genotype. A similar association was observed in an independent, dataset of nondemented subjects (n = 278), although with a smaller effect (1%). This replicated association with GM structural variation suggests that GOLM1 polymorphisms may be related to cognitive phenotypes. The greater effect size in AD patients also suggests that the GG genotype could be a risk factor for the expression of cognitive deficits in AD.     

Association of HLA-DRB1 and TNF genotypes with dengue hemorrhagic fever

Genes coding for human leukocyte antigen (HLA) class II molecules and tumor necrosis factor (TNF)-α are polymorphic and have been shown to influence susceptibility to infectious diseases. In the present study, HLA-DRB1, -DQB1 and TNF gene polymorphisms were investigated in 114 dengue patients (DEN) [85 dengue fever (DF) cases and 29 dengue hemorrhagic fever (DHF) cases] and 110 healthy controls (HCs) using PCR based methods. The frequencies of HLA-DRB1^∗07 allele [DF vs. DHF, P = 0.0034, Pc = 0.044, OR 3.79] and HLA-DRB1^∗07/^∗15 genotype [DF vs. DHF, P = 0.00071, Pc = 0.038, OR 10.41] were significantly higher in DHF cases as compared to HCs and DF cases. Higher frequency of rs1800629 ‘G/A’ genotype was observed in DHF cases as compared to DF cases. The frequency of rs1799964 ‘C/C’ genotype of the TNF gene was found to be significantly higher in all patient groups compared to HCs [HCs vs. DEN, P = 0.0054, Pc = 0.0162, OR 3.57; HCs vs. DF, P = 0.036, OR 2.89; HCs vs. DHF, P = 0.0088, Pc = 0.0240, OR 5.11]. Presence of combination of HLA-DRB1^∗07/^∗15 with either rs1799964 ‘C/C’ genotype or rs1800629 ‘G/A’ genotype or both was present in 17.2% of DHF cases and 1.2% in HCs while this combination was not observed in DF cases. The results suggest that HLA-DRB1^∗07/^∗15 genotype in combination with TNF polymorphisms influence progression to DHF.     

Association study of the paraoxonase 1 gene with the risk of developing Alzheimer's disease

Recently, a region encompassing the promoter and intron 1 of the paraoxonase 1 gene (PON1) have been associated with the risk of developing Alzheimer's disease (AD) in a large pan-ethnic (Caucasian and African-American) dataset. We attempted to replicate this observation in a large French study of sporadic cases and controls. We confirmed that the proximal promoter and 5' sequence of the PON1 gene may harbor unknown functional variant(s) associated with the risk of developing AD.     

Association and heterogeneity at the GAPDH locus in Alzheimer's disease

Glyceraldehyde-3-phosphate dehydrogenase gene (GAPDH) and its paralogs were implicated in late-onset Alzheimer's disease (LOAD), although the strength and direction of association have not been consistent. We genotyped 3 previously reported single nucleotide polymorphisms (SNPs; rs3741916-GAPDH 5′ UTR, rs2029721-pGAPD, and rs4806173-GAPDHS) in 3 case-control series (2112 cases and 3808 controls). Rs3741916 showed the strongest LOAD association (p = 0.003). The minor allele of rs3741916 showed a protective effect in our combined series (odds ratio [OR] = 0.87%, 95% confidence interval [CI] = 0.79-0.96). This is consistent with results from the 2 published follow-up studies and in opposite direction of the original report. Meta-analysis of the published series with ours suggests presence of heterogeneity (Breslow-Day p < 0.0001). Meta-analysis of only the follow-up series including ours revealed a significant protective effect for the minor allele of rs3741916 (OR = 0.85%, 95% CI = 0.76-0.96, p = 0.009). Our results support the presence of LOAD variants and heterogeneity at the GAPDH locus. The most promising rs3741916 variant is unlikely to be functional given opposing effects in different series. Identification of functional variant(s) in this region likely awaits deep sequencing.     

Association of the aromatase gene with Alzheimer's disease in women

Associations have been reported of aromatase polymorphisms with Alzheimer's disease (AD). We studied nine polymorphisms in 207 cases of AD, 23 cases of mild cognitive impairment (MCI) and 233 controls, all from the OPTIMA cohort. We replicated two reported associations and found others. Our findings were consistent between AD and MCI. Further, our results were sex-specific, i.e. there were significant interactions between certain polymorphisms and gender, and the associations with AD were almost entirely in women. Aromatase catalyses the conversion of androgens to estrogens. It is expressed in the human brain. In the hippocampus, it is upregulated in postmenopausal women and is lowered in AD. These sex-specific results are therefore plausible. However, our results now need to be replicated in a larger dataset.     

Insulin-like growth factor 1 (IGF1) polymorphism is associated with Alzheimer's disease in Han Chinese

A review of pathogenic findings in Alzheimer's brains and the functional consequences of altered insulin-like growth factor 1 (IGF1) input to the brain suggest the association between Alzheimer's disease (AD) and the disrupted IGF1 signaling. Recently, the identification of polymorphism rs972936 that was associated with both an increased risk of AD and high circulating levels of IGF1 was reported in Southern European population. In order to evaluate the involvement of the IGF1 polymorphism in the risk of developing late-onset Alzheimer's disease (LOAD) in Chinese, we performed an independent case-control association study in a Han Chinese population (794 LOAD cases and 796 controls). There were significant differences in genotype and allele frequencies between LOAD cases and controls (genotype P = 0.006, allele P = 0.047). The T allele of rs972936 demonstrated a 1.16-fold risk for developing LOAD when compared with the C allele, which diverges to the report in the Caucasian population. After stratification by apolipoprotein E (APOE) ?4-carrying status, rs972936 polymorphism was only significantly associated with LOAD in non-ApoE ?4 allele carriers (genotype P = 0.002, allele P = 0.039). Multivariate logistic regression analysis also conferred this positive association between the SNP rs972936 and LOAD in the recessive and additive model after adjustment for age, gender, and the ApoE ?4 carrier status. These results suggest that IGF1 polymorphism has a possible role in changing the genetic susceptibility to LOAD in a Han Chinese population.     

A novel presenilin 1 mutation (Ser169del) in a Chinese family with early-onset Alzheimer's disease

Early-onset familial Alzheimer's disease (EOFAD) has been associated with mutations in three genes, of which presenilin 1 (PSEN1) mutations are the most frequent. Here we report a novel PSEN1 mutation in a Chinese family with autosomal dominant Alzheimer's disease with an onset age in the early 40s. Molecular genetic analysis showed a 507-509delATC mutation at codon 169, leading to the deletion of serine in residue 169 (Ser169del). The amnestic presentation and absence of other features contrast with the other two mutations at codon 169 which have been associated with myoclonic jerks and seizures.