Relevance of the COPI complex for Alzheimer's disease progression in vivo.

Cellular trafficking and recycling machineries belonging to late secretory compartments have been associated with increased Alzheimer's disease (AD) risk. We have shown that coat protein complex I (COPI)-dependent trafficking, an early step in Golgi-to-endoplasmic reticulum retrograde transport, affects amyloid precursor protein subcellular localization, cell-surface expression, as well as its metabolism. We present here a set of experiments demonstrating that, by targeting subunit δ-COP function, the moderation of the COPI-dependent trafficking in vivo leads to a significant decrease in amyloid plaques in the cortex and hippocampus of neurological 17 mice crossed with the 2xTg AD mouse model. Remarkably, an improvement of the memory impairments was also observed. Importantly, human genetic association studies of different AD cohorts led to the identification of 12 SNPs and 24 mutations located in COPI genes linked to an increased AD risk. These findings further demonstrate in vivo the importance of early trafficking steps in AD pathogenesis and open new clinical perspectives.

Variations in the FRA10AC1 Fragile Site and 15q21 Are Associated with Cerebrospinal Fluid Aß1-42 Level.

Proteolytic fragments of amyloid and post-translational modification of tau species in Cerebrospinal fluid (CSF) as well as cerebral amyloid deposition are important biomarkers for Alzheimer's Disease. We conducted genome-wide association study to identify genetic factors influencing CSF biomarker level, cerebral amyloid deposition, and disease progression. The genome-wide association study was performed via a meta-analysis of two non-overlapping discovery sample sets to identify genetic variants other than APOE ε4 predictive of the CSF biomarker level (Aß1-42, t-Tau, p-Tau181P, t-Tau:Aß1-42 ratio, and p-Tau181P:Aß1-42 ratio) in patients enrolled in the Alzheimer's Disease Neuroimaging Initiative (ADNI) study. Loci passing a genome-wide significance threshold of P < 5 x 10-8 were followed-up for replication in an independent sample set. We also performed joint meta-analysis of both discovery sample sets together with the replication sample set. In the discovery phase, we identified variants in FRA10AC1 associated with CSF Aß1-42 level passing the genome-wide significance threshold (directly genotyped SNV rs10509663 PFE = 1.1 x 10-9, imputed SNV rs116953792 PFE = 3.5 x 10-10), rs116953792 (Pone-sided = 0.04) achieved replication. This association became stronger in the joint meta-analysis (directly genotyped SNV rs10509663 PFE = 1.7 x 10-9, imputed SNV rs116953792 PFE = 7.6 x 10-11). Additionally, we identified locus 15q21 (imputed SNV rs1503351 PFE = 4.0 x 10-8) associated with CSF Aß1-42 level. No other variants passed the genome-wide significance threshold for other CSF biomarkers in either the discovery sample sets or joint analysis. Gene set enrichment analyses suggested that targeted genes mediated by miR-33, miR-146, and miR-193 were enriched in various GWAS analyses. This finding is particularly important because CSF biomarkers confer disease susceptibility and may be predictive of the likelihood of disease progression in Alzheimer's Disease.

The rare TREM2 R47H variant exerts only a modest effect on Alzheimer disease risk.

OBJECTIVES: Recently, 2 independent studies reported that a rare missense variant, rs75932628 (R47H), in exon 2 of the gene encoding the "triggering receptor expressed on myeloid cells 2" (TREM2) significantly increases the risk of Alzheimer disease (AD) with an effect size comparable to that of the APOE ε4 allele. METHODS: In this study, we attempted to replicate the association between rs75932628 and AD risk by directly genotyping rs75932628 in 2 independent Caucasian family cohorts consisting of 927 families (with 1,777 affected and 1,235 unaffected) and in 2 Caucasian case-control cohorts composed of 1,314 cases and 1,609 controls. In addition, we imputed genotypes in 3 independent Caucasian case-control cohorts containing 1,906 cases and 1,503 controls. RESULTS: Meta-analysis of the 2 family-based and the 5 case-control cohorts yielded a p value of 0.0029, while the overall summary estimate (using case-control data only) resulted in an odds ratio of 1.67 (95% confidence interval 0.95-2.92) for the association between the TREM2 R47H and increased AD risk. CONCLUSIONS: While our results serve to confirm the association between R47H and risk of AD, the observed effect on risk was substantially smaller than that previously reported.

Elucidation of the BACE1 regulating factor GGA3 in Alzheimer's disease.

Golgi-localized γ-ear-containing ADP-ribosylation factor-binding protein (GGA3) is a central regulator of trafficking and degradation of BACE1 (ß-site AßPP-cleaving enzyme), the rate-limiting enzyme in the production of amyloid-ß (Aß) in Alzheimer's disease (AD). Here, we assessed the potential role of GGA3 in AD pathogenesis using independent neuropathological, case-control, and family-based human sample cohorts. Increased BACE1 levels coincided with decreased GGA3 levels and with elevated phosphorylation status of eIF2α-Ser51 in the temporal cortex of AD patients as compared to age-matched controls. Severity of the disease did not alter mRNA or protein levels of GGA3 in the inferior temporal cortex of AD patients, while a positive correlation between GGA3 and the levels of total, but not phosphorylated, tau was observed. Genetically, we did not observe consistent evidence for association between AD risk and common GGA3 polymorphisms across a number of independent sample cohorts. However, a nominally significant association was observed with rs2242230 (p < 0.05) among the Finnish case-control cohort. Accordingly, mRNA and protein levels of GGA3 in the inferior temporal cortex of AD patients did not significantly correlate with rs2242230 genotype status. While the present study indicates that GGA3 is involved in the cellular processes relevant for AD pathogenesis, the genetic data do not support the idea that common GGA3 polymorphisms would contribute to AD risk.

Alzheimer's disease risk gene CD33 inhibits microglial uptake of amyloid beta.

The transmembrane protein CD33 is a sialic acid-binding immunoglobulin-like lectin that regulates innate immunity but has no known functions in the brain. We have previously shown that the CD33 gene is a risk factor for Alzheimer's disease (AD). Here, we observed increased expression of CD33 in microglial cells in AD brain. The minor allele of the CD33 SNP rs3865444, which confers protection against AD, was associated with reductions in both CD33 expression and insoluble amyloid beta 42 (Aß42) levels in AD brain. Furthermore, the numbers of CD33-immunoreactive microglia were positively correlated with insoluble Aß42 levels and plaque burden in AD brain. CD33 inhibited uptake and clearance of Aß42 in microglial cell cultures. Finally, brain levels of insoluble Aß42 as well as amyloid plaque burden were markedly reduced in APP(Swe)/PS1(ΔE9)/CD33(-/-) mice. Therefore, CD33 inactivation mitigates Aß pathology and CD33 inhibition could represent a novel therapy for AD.

Multiple loci influencing hippocampal degeneration identified by genome scan.

OBJECTIVE: Large genome-wide association studies (GWASs) have identified many novel genes influencing Alzheimer disease (AD) risk, but most of the genetic variance remains unexplained. We conducted a 2-stage GWAS for AD-related quantitative measures of hippocampal volume (HV), total cerebral volume (TCV), and white matter hyperintensities (WMH). METHODS: Brain magnetic resonance imaging measures of HV, TCV, and WMH were obtained from 981 Caucasian and 419 African American AD cases and their cognitively normal siblings in the MIRAGE (Multi Institutional Research in Alzheimer's Genetic Epidemiology) Study, and from 168 AD cases, 336 individuals with mild cognitive impairment, and 188 controls in the Alzheimer's Disease Neuroimaging Initiative Study. A GWAS for each trait was conducted in the 2 Caucasian data sets in stage 1. Results from the 2 data sets were combined by meta-analysis. In stage 2, 1 single nucleotide polymorphism (SNP) from each region that was nominally significant in each data set (p < 0.05) and strongly associated in both data sets (p < 1.0 × 10(-5)) was evaluated in the African American data set. RESULTS: Twenty-two markers (14 for HV, 3 for TCV, and 5 for WMH) from distinct regions met criteria for evaluation in stage 2. Novel genome-wide significant associations (p < 5.0 × 10(-8)) were attained for HV with SNPs in the APOE, F5/SELP, LHFP, and GCFC2 gene regions. All of these associations were supported by evidence in each data set. Associations with different SNPs in the same gene (p < 1 × 10(-5) in Caucasians and p < 2.2 × 10(-4) in African Americans) were also observed for PICALM with HV, SYNPR with TCV, and TTC27 with WMH. INTERPRETATION: Our study demonstrates the efficacy of endophenotypes for broadening our understanding of the genetic basis of AD.

Cysteine 27 variant of the delta-opioid receptor affects amyloid precursor protein processing through altered endocytic trafficking.

Agonist-induced activation of the δ-opioid receptor (δOR) was recently shown to augment ß- and γ-secretase activities, which increased the production of ß-amyloid peptide (Aß), known to accumulate in the brain tissues of Alzheimer's disease (AD) patients. Previously, the δOR variant with a phenylalanine at position 27 (δOR-Phe27) exhibited more efficient receptor maturation and higher stability at the cell surface than did the less common cysteine (δOR-Cys27) variant. For this study, we expressed these variants in human SH-SY5Y and HEK293 cells expressing exogenous or endogenous amyloid precursor protein (APP) and assessed the effects on APP processing. Expression of δOR-Cys27, but not δOR-Phe27, resulted in a robust accumulation of the APP C83 C-terminal fragment and the APP intracellular domain, while the total soluble APP and, particularly, the ß-amyloid 40 levels were decreased. These changes upon δOR-Cys27 expression coincided with decreased localization of APP C-terminal fragments in late endosomes and lysosomes. Importantly, a long-term treatment with a subset of δOR-specific ligands or a c-Src tyrosine kinase inhibitor suppressed the δOR-Cys27-induced APP phenotype. These data suggest that an increased constitutive internalization and/or concurrent signaling of the δOR-Cys27 variant affects APP processing through altered endocytic trafficking of APP.

Dengue hemorrhagic fever is associated with polymorphisms in JAK1.

To identify genes associated with the clinical presentation of dengue, 50 cases of probable or possible dengue hemorrhagic fever (DHF), 236 dengue fever (DF), and 236 asymptomatic infections were genotyped for 593 single-nucleotide polymorphisms (SNPs) in 56 genes across the type 1 interferon (IFN) response pathway as well as other important candidate genes. By single locus analysis comparing DHF with DF, 11 of the 51 markers with P<0.05 were in the JAK1 gene. Five markers were significantly associated by false discovery rate criteria (q<0.20 when P<6 × 10(-4)). The JAK1 SNPs showed differential distribution by ethnicity and ancestry consistent with epidemiologic observations in the Americas. The association remained significant after controlling for ancestry and income. No association was observed with markers in the gene encoding CD209 (DC-SIGN). An association between DHF and JAK1 polymorphisms is in agreement with expression profiles showing generalized decreased type 1 IFN-stimulated gene expression in these patients.

Genetic ancestry and income are associated with dengue hemorrhagic fever in a highly admixed population.

To test whether African ancestry is protective for severe dengue, we genotyped 49 hospitalized cases of dengue hemorrhagic fever (DHF) as well as 293 neighborhood cases of dengue fever and 294 asymptomatic controls in Salvador, Bahia, Brazil. Ancestry-informative markers and 282 unlinked SNPs not associated with the clinical presentation of dengue were used to estimate ancestry. After controlling for income, both self-defined Afro-Brazilian ethnicity and African ancestry were protective for DHF (P=0.02, OR=0.28 and P=0.02, OR=0.13, respectively). Income or an index of income indicators, however, was also independently associated with the diagnosis of DHF.

Association of kallikrein gene polymorphisms with intracranial aneurysms.

BACKGROUND AND PURPOSE: Genomewide DNA linkage analysis identified a susceptibility locus for intracranial aneurysm (IA) on chromosome 19q13 in the Finnish population, a region including the kallikrein gene cluster. We investigated the association of single nucleotide polymorphisms (SNPs) in the kallikrein gene cluster with IA in the Finnish population. METHODS: We genotyped 18 haplotype-tagging SNPs spanning a 244 kbp region in the kallikrein gene cluster for 266 Finnish IA cases and 290 Finnish control subjects. In a second phase, we genotyped 2 SNPs (rs1722561 and rs1701946) in an additional set of 102 Finnish IA cases and 102 Finnish control subjects; and in a third phase, we genotyped these 2 SNPs in 156 Russian IA cases and 186 Russian control subjects. Both single-marker and haplotype-based tests of association were performed. RESULTS: In phase I, SNPs rs1722561 and rs1701946 were significantly associated with IA in the Finnish population for single locus models (rs1722561: P=0.0395; rs1701946: P=0.0253). A 2-SNP haplotype block (rs1722561-rs1701946) identified in phase I was also associated with IA in the expanded Finnish (phase II) data set (asymptotic P=0.012; empirical P=0.019). In the Finnish and Russian combined data set (phase III) with 524 cases and 578 control subjects, the same 2 SNPs (OR: 1.35, 95% CI: 1.14, 1.60; P=0.0005 for rs1722561 and OR: 1.32, 95% CI: 1.12, 1.57; P=0.0011 for rs1701946) were significantly associated with IA. These SNPs are located in the intronic region of KLK8, although linkage disequilibrium could extend from rs268912-rs2250066, a approximately 76-kbp region that includes KLK5-KLK10. CONCLUSIONS: Polymorphisms within the kallikrein gene cluster are associated with IA suggesting that the kallikreins are important candidate genes for IA.

Density-based clustering in haplotype analysis for association mapping.

Clustering of related haplotypes in haplotype-based association mapping has the potential to improve power by reducing the degrees of freedom without sacrificing important information about the underlying genetic structure. We have modified a generalized linear model approach for association analysis by incorporating a density-based clustering algorithm to reduce the number of coefficients in the model. Using the GAW 15 Problem 3 simulated data, we show that our novel method can substantially enhance power to detect association with the binary rheumatoid arthritis (RA) phenotype at the HLA-DRB1 locus on chromosome 6. In contrast, clustering did not appreciably improve performance at locus D, perhaps a consequence of a rare susceptibility allele and of the overwhelming effect of HLA-DRB1/locus C, 5 cM distal. Optimization of parameters governing the clustering algorithm identified a set of parameters that delivered nearly ideal performance in a variety of situations. The cluster-based score test was valid over a wide range of haplotype diversity, and was robust to severe departures from Hardy-Weinberg equilibrium encountered near HLA-DRB1 in RA case-control samples.

HLA-DQA is associated with abdominal aortic aneurysms in the Belgian population.

Chronic inflammation and autoimmunity likely contribute to the pathogenesis of abdominal aortic aneurysms (AAAs). The aim of this study was to investigate the role of autoimmunity in the etiology of AAAs using a genetic association study approach with human leukocyte antigen (HLA) polymorphisms (HLA-DQA1, -DQB1, -DRB1 and -DRB3-5 alleles) in 387 AAA cases and 426 controls. We observed an association with the HLA-DQA1 locus among Belgian males, and found a significant difference in the HLA-DQA1*0102 allele frequencies between AAA cases and controls. In conclusion, this study showed potential evidence that the HLA-DQA1 locus harbors a genetic risk factor for AAAs suggesting that autoimmunity plays a role in the pathogenesis of AAAs.

Evidence for association between the HLA-DQA locus and abdominal aortic aneurysms in the Belgian population: a case control study.

BACKGROUND: Chronic inflammation and autoimmunity likely contribute to the pathogenesis of abdominal aortic aneurysms (AAAs). The aim of this study was to investigate the role of autoimmunity in the etiology of AAAs using a genetic association study approach with HLA polymorphisms. METHODS: HLA-DQA1, -DQB1, -DRB1 and -DRB3-5 alleles were determined in 387 AAA cases (180 Belgian and 207 Canadian) and 426 controls (269 Belgian and 157 Canadian) by a PCR and single-strand oligonucleotide probe hybridization assay. RESULTS: We observed a potential association with the HLA-DQA1 locus among Belgian males (empirical p = 0.027, asymptotic p = 0.071). Specifically, there was a significant difference in the HLA-DQA1*0102 allele frequencies between AAA cases (67/322 alleles, 20.8%) and controls (44/356 alleles, 12.4%) in Belgian males (empirical p = 0.019, asymptotic p = 0.003). In haplotype analyses, marginally significant association was found between AAA and haplotype HLA-DQA1-DRB1 (p = 0.049 with global score statistics and p = 0.002 with haplotype-specific score statistics). CONCLUSION: This study showed potential evidence that the HLA-DQA1 locus harbors a genetic risk factor for AAAs suggesting that autoimmunity plays a role in the pathogenesis of AAAs.

Linkage analysis of alcoholism-related electrophysiological phenotypes: genome scans with microsatellites compared to single-nucleotide polymorphisms.

P300 amplitude is an electrophysiological quantitative trait that is correlated with both alcoholism and smoking status. Using the Collaborative Study on the Genetics of Alcoholism data, we performed model-free linkage analysis to investigate the relationship between alcoholism, P300 amplitude, and habitual smoking. We also analyzed the effect of parent-of-origin on alcoholism, and utilized both microsatellites (MS) markers and single-nucleotide polymorphisms (SNPs). We found significant evidence of linkage for alcoholism to chromosome 10; inclusion of P300 amplitude as a covariate provided additional evidence of linkage to chromosome 12. This same region on chromosome 12 showed some evidence for a parent-of-origin effect. We found evidence of linkage for the P300 phenotype to chromosome 7 in non-smokers, and to chromosome 17 in alcoholics. The effects of alcoholism and habitual smoking on P300 amplitude appear to have separate genetic determinants. Overall, there were few differences between MS and SNP genome scans. The use of covariates and parent-of-origin effects allowed detection of linkage not seen otherwise.

Identification of Barrett's esophagus in relatives by endoscopic screening.

AIM: Familial aggregation of Barrett's esophagus and its associated cancers has been termed familial Barrett's esophagus (FBE). The aim of the study was to determine whether endoscopic screening would identify Barrett's esophagus (BE) in relatives of probands with BE or esophageal adenocarcinoma (EAC). METHODS: All living first-degree relatives of patients with long segment BE or EAC presenting to the endoscopy suite of two academic hospitals were sent validated questionnaires inquiring about gastroesophageal reflux symptoms and prior endoscopic evaluation. First-degree relatives of affected probands or affected relatives who reported no prior upper endoscopy were offered screening unsedated esophagoscopy. Relatives with chronic gastroesophageal reflux symptoms were also offered an alternative of conventional sedated upper endoscopy. The yield of screening endoscopy was measured. Screening endoscopy findings were then compared between family members of known FBE patients and those with "isolated" disease. RESULTS: One hundred and ninety-eight relatives from 69 families, 23 known FBE probands and 46 probands with apparently "isolated" disease, were enrolled. Forty relatives (29 FBE relatives and 11 relatives of probands with "isolated" disease) reported prior upper endoscopy. Screening upper endoscopies performed on 62 (25 FBE and 37 "isolated" disease relatives) of the remaining 158 relatives identified Barrett's epithelium in 13 (21%). Compared to probands with apparently "isolated" disease, Barrett's epithelium (EAC, BE, or SSBE) was identified significantly more often in siblings and offspring of FBE probands, p

Map error reduction: using genetic and sequence-based physical maps to order closely linked markers.

The Marshfield comprehensive genetic maps are frequently used for linkage and association studies, however, for some regions of these maps the marker order has low level of likelihood ratio support. In order to investigate the level of statistical support and the accuracy of the genetic maps compared to sequence-based physical maps, two approximately 30 cM autosomal regions were selected. The first region was selected from chromosome 3 and consisted predominately of draft sequence. The second region was selected from chromosome 21 and consisted of finished sequence data. The physical order of these markers was based upon their position on Celera (CEL) and Human Genome Project-Santa Cruz (HGP-sc) sequence-based physical maps. The chromosome 3 and 21 regions contained 100 and 61 markers, respectively, on the Marshfield genetic map. The genetic and physical map order was consistent for 88.9 and 89.2% of the markers in the region on chromosome 3 and 21, respectively. Using a novel scoring criterion to assess inconsistent marker order between genetic and physical maps, it was determined that the physical order was likely the correct order for 3.3 and 7.1% of the markers in the chromosome 3 and 21 regions, respectively. To increase the accuracy of the order of markers selected for fine mapping a method is presented which combines information from genetic and sequence-based physical maps.

The map problem: a comparison of genetic and sequence-based physical maps.

The genetic order of autosomal genome-scan markers from Marshfield panels 9 and 10 were compared with their physical order, on the basis of the assembled nonredundant human genome sequence from the Human Genome Project-Santa Cruz (HGP-sc; October 2000 and April 2001 releases) and Celera (CEL; February 2001 release) databases. The genetic order of 96% of the markers on the Marshfield map for panel 10 is supported by a likelihood ratio of > or = 3 (odds ratio of 1,000:1). Inconsistencies with the genetic panel 10 map were found for 5% and 2% of the markers in the CEL and HGP-sc sequences, respectively. These inconsistencies consisted of both positional and chromosomal-assignment disagreements. For the majority of these inconsistent markers, the genetic order was supported by a likelihood ratio of > or = 3, and the physical order in the other assembly matched the genetic order. The majority of the inconsistencies between the physical- and genetic-map order point to errors in the physical-map order. A Web site is made available that displays inconsistencies for genetic markers from Marshfield panels 9 and 10 between their genetic-map positions and sequence-based physical-map positions, as well as inconsistencies between their sequence-based physical position. This Web site also contains genetic-map distances, physical-map positions from the Celera and Human Genome Project sequence, and likelihood-ratio support for the genetic maps.