Evidence for an Alzheimer disease susceptibility locus on chromosome 12 and for further locus heterogeneity

Deficient Wnt Signaling and Synaptic Vulnerability in Alzheimer's Disease: Emerging Roles for the LRP6 Receptor

Synapse dysfunction and loss represent critical early events in the pathophysiology of Alzheimer’s disease (AD). While extensive research has elucidated the direct synaptotoxic effects of Amyloid-β (Aβ) oligomers, less is known about how signaling pathways at the synapse are affected by Aβ. A better understanding of the cellular and molecular mechanisms underlying synaptic vulnerability in AD is key to illuminating the determinants of AD susceptibility and will unveil novel therapeutic avenues. Canonical Wnt signaling through the Wnt co-receptor LRP6 has a critical role in maintaining the structural and functional integrity of synaptic connections in the adult brain. Accumulating evidence suggests that deficient Wnt signaling may contribute to AD pathology. In particular, LRP6 deficiency compromises synaptic function and stability, and contributes to Aß production and plaque formation. Here, we review the role of Wnt signaling for synaptic maintenance in the adult brain and the contribution of aberrant Wnt signaling to synaptic degeneration in AD. We place a focus on emerging evidence implicating the LRP6 receptor as an important modulator of AD risk and pathology.

Genomic variants, genes, and pathways of Alzheimer's disease: An overview

Alzheimer's disease (AD) (MIM: 104300) is a highly heritable disease with great complexity in its genetic contributors, and represents the most common form of dementia. With the gradual aging of the world's population, leading to increased prevalence of AD, and the substantial cost of care for those afflicted, identifying the genetic causes of disease represents a critical effort in identifying therapeutic targets. Here we provide a comprehensive review of genomic studies of AD, from the earliest linkage studies identifying monogenic contributors to early-onset forms of AD to the genome-wide and rare variant association studies of recent years that are being used to characterize the mosaic of genetic contributors to late-onset AD (LOAD), and which have identified approximately ∼20 genes with common variants contributing to LOAD risk. In addition, we explore studies employing alternative approaches to identify genetic contributors to AD, including studies of AD-related phenotypes and multi-variant association studies such as pathway analyses. Finally, we introduce studies of next-generation sequencing, which have recently helped identify multiple low-frequency and rare variant contributors to AD, and discuss on-going efforts with next-generation sequencing studies to develop statistically well- powered and comprehensive genomic studies of AD. Through this review, we help uncover the many insights the genetics of AD have provided into the pathways and pathophysiology of AD. © 2016 Wiley Periodicals, Inc.

Genomics and CSF analyses implicate thyroid hormone in hippocampal sclerosis of aging

We report evidence of a novel pathogenetic mechanism in which thyroid hormone dysregulation contributes to dementia in elderly persons. Two single nucleotide polymorphisms (SNPs) on chromosome 12p12 were the initial foci of our study: rs704180 and rs73069071. These SNPs were identified by separate research groups as risk alleles for non-Alzheimer's neurodegeneration. We found that the rs73069071 risk genotype was associated with hippocampal sclerosis (HS) pathology among people with the rs704180 risk genotype (National Alzheimer's Coordinating Center/Alzheimer's Disease Genetic Consortium data; n = 2113, including 241 autopsy-confirmed HS cases). Furthermore, both rs704180 and rs73069071 risk genotypes were associated with widespread brain atrophy visualized by MRI (Alzheimer's Disease Neuroimaging Initiative data; n = 1239). In human brain samples from the Braineac database, both rs704180 and rs73069071 risk genotypes were associated with variation in expression of ABCC9, a gene which encodes a metabolic sensor protein in astrocytes. The rs73069071 risk genotype was also associated with altered expression of a nearby astrocyte-expressed gene, SLCO1C1. Analyses of human brain gene expression databases indicated that the chromosome 12p12 locus may regulate particular astrocyte-expressed genes induced by the active form of thyroid hormone, triiodothyronine (T3). This is informative biologically, because the SLCO1C1 protein transports thyroid hormone into astrocytes from blood. Guided by the genomic data, we tested the hypothesis that altered thyroid hormone levels could be detected in cerebrospinal fluid (CSF) obtained from persons with HS pathology. Total T3 levels in CSF were elevated in HS cases (p < 0.04 in two separately analyzed groups), but not in Alzheimer's disease cases, relative to controls. No change was detected in the serum levels of thyroid hormone (T3 or T4) in a subsample of HS cases prior to death. We conclude that brain thyroid hormone perturbation is a potential pathogenetic factor in HS that may also provide the basis for a novel CSF-based clinical biomarker.

Genetics of Alzheimer's disease in Caribbean Hispanic and African American populations

Late-onset Alzheimer's disease (LOAD), which is characterized by progressive deterioration in cognition, function, and behavior, is the most common cause of dementia and the sixth leading cause of all deaths, placing a considerable burden on Western societies. Most studies aiming to identify genetic susceptibility factors for LOAD have focused on non-Hispanic white populations. This is, in part related to differences in linkage disequilibrium and allele frequencies between ethnic groups that could lead to confounding. However, in addition, non-Hispanic white populations are simply more widely studied. As a consequence, minorities are genetically underrepresented despite the fact that in several minority populations living in the same community as whites (including African American and Caribbean Hispanics), LOAD incidence is higher. This review summarizes the current knowledge on genetic risk factors associated with LOAD risk in Caribbean Hispanics and African Americans and provides suggestions for future research. We focus on Caribbean Hispanics and African Americans because they have a high LOAD incidence and a body of genetic studies on LOAD that is based on samples with genome-wide association studies data and reasonably large effect sizes to yield generalizable results.

Risk factors for dementia in a senegalese elderly population aged 65 years and over

Background

With the aging of the population, dementia is increasing worldwide. The objective of this study was to identify risk factors for dementia in an elderly population utilizing a primary health care service in Dakar, Senegal.

Methods

Through a cross-sectional study conducted from March 2004 to December 31, 2005, 507 elderly patients aged ≥65 years who came to the Social and Medical Center of IPRES, Dakar, Senegal, were first screened with the screening interview questionnaire ‘Aging in Senegal’. Those who were cognitively impaired underwent a clinical examination to detect dementia. Univariate, bivariate, and multivariate logistic regression analyses were done.

Results

The whole population had a mean age of 72.4 years (±5.2) and was mostly male, married, and non-educated. Hypertension, arthritis, and gastrointestinal diseases were the main health conditions reported in the past medical history. Smoking was important while alcohol consumption was rare. Social network was high. Forty-five patients (8.87%) had dementia. In the multivariate model, only advanced age, education, epilepsy, and family history of dementia were independently associated with dementia.

Conclusion

The risk factors identified are also found in developed countries confirming their role in dementia. It is important to take dementia into consideration in Senegal and to sensitize the community for prevention.

Vitamin D receptor and Alzheimer's disease: a genetic and functional study

Genetic studies on late-onset Alzheimer's disease (AD) have repeatedly mapped susceptibility loci onto chromosome 12q13, encompassing the vitamin D receptor (VDR) gene. Epidemiology studies have indicated vitamin D insufficiency as a risk factor for AD. Given that VDR is the major mediator for vitamin D's actions, we sought to clarify the role of VDR in late-onset AD. We conducted an association study in 492 late-onset AD cases and 496 controls with 80 tagging single nucleotide polymorphisms (SNPs). The strongest association was found at a promoter SNP rs11568820 (P = 9.1 × 10(-6), odds ratio (OR) = 1.69), which resides within the transcription factor Cdx-2 binding site and the SNP has been also known as CDX2. The risk-allele at rs11568820 is associated with lower VDR promoter activity (p < 10(-11)). The overexpression of VDR or vitamin D treatment suppressed amyloid precursor protein (APP) transcription in neuroblastoma cells (p < 0.001). We provide both statistical evidence and functional data suggesting VDR confers genetic risk for AD. Our findings are consistent with epidemiology studies suggesting that vitamin D insufficiency increases the risk of developing AD.

Identification of novel candidate genes for Alzheimer's disease by autozygosity mapping using genome wide SNP data

Alzheimer's disease (AD) is highly prevalent in Wadi Ara despite the low frequency of apolipoprotein E ε4 in this genetically isolated Arab community in northern Israel. We hypothesized that the reduced genetic variability in combination with increased homozygosity would facilitate identification of genetic variants that contribute to the high rate of AD in this community. AD cases (n = 124) and controls (n = 142) from Wadi Ara were genotyped for a genome-wide set of more than 300,000 single nucleotides polymorphisms (SNPs) which were used to calculate measures of population stratification and inbreeding, and to identify regions of autozygosity. Although a high degree of relatedness was evident in both AD cases and controls, controls were significantly more related and contained more autozygous regions than AD cases (p = 0.004). Eight autozygous regions on seven different chromosomes were more frequent in controls than the AD cases, and 116 SNPs in these regions, primarily on chromosomes 2, 6, and 9, were nominally associated with AD. The association with rs3130283 in AGPAT1 on chromosome 6 was observed in a meta-analysis of seven genome-wide association study (GWAS) datasets. Analysis of the full Wadi Ara GWAS dataset revealed 220 SNP associations with AD at p ≤ 10⁻⁵, and seven of these were confirmed in the replication GWAS datasets (p < 0.05). The unique population structure of Wadi Ara enhanced efforts to identify genetic variants that might partially explain the high prevalence of AD in the region. Several of these variants show modest evidence for association in other Caucasian populations.

Genetic association of rs11610206 SNP on chromosome 12q13 with late-onset Alzheimer's disease in a Han Chinese population

BACKGROUND

Several genome wide screens and candidate gene studies have implicated the chromosome 12p13 locus as possibly harboring genetic variants predisposed to late-onset Alzheimer's disease (LOAD). Recently, the strongest significant association was reported for the single nucleotide polymorphism (SNP) rs11610206 on chromosome 12q13 in an independent genome-wide association study (GWAS) in Caucasians.

METHODS

We investigated whether the SNP on chromosome 12q13 was associated with LOAD in a Han Chinese population. The common rs11610206 SNP on chromosome 12q13 was genotyped using MALDI-TOF mass spectrometry in 322 patients with LOAD and in 391 healthy controls matched for sex and age.

RESULTS

Patients with LOAD had higher frequencies of T allele (56.0% versus 49.2%) compared with controls [odds ratio (OR)=1.45, 95% confidence intervals (CI)=1.08-1.95, and P=0.01]. After stratification by APOE ε4-carrying status, the T allele of rs11610206 was significantly associated with LOAD only in APOE ε4 allele carriers (OR=2.05, 95% CI=1.21-3.47, and P=0.007). Furthermore, multivariate logistic regression analysis showed that the TT genotype carriers demonstrated a 1.52-fold risk when compared with (TC+CC) genotype carriers (OR=1.52, 95% CI=1.07-2.17, and P=0.02).

CONCLUSIONS

This study demonstrates an association of rs11610206 polymorphism locus on chromosome 12q13 with risk for LOAD in Han Chinese.

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.

Gene expression profiling in cells with enhanced gamma-secretase activity

Background

Processing by γ-secretase of many type-I membrane protein substrates triggers signaling cascades by releasing intracellular domains (ICDs) that, following nuclear translocation, modulate the transcription of different genes regulating a diverse array of cellular and biological processes. Because the list of γ-secretase substrates is growing quickly and this enzyme is a cancer and Alzheimer's disease therapeutic target, the mapping of γ-secretase activity susceptible gene transcription is important for sharpening our view of specific affected genes, molecular functions and biological pathways.

Methodology/Principal Findings

To identify genes and molecular functions transcriptionally affected by γ-secretase activity, the cellular transcriptomes of Chinese hamster ovary (CHO) cells with enhanced and inhibited γ-secretase activity were analyzed and compared by cDNA microarray. The functional clustering by FatiGO of the 1,981 identified genes revealed over- and under-represented groups with multiple activities and functions. Single genes with the most pronounced transcriptional susceptibility to γ-secretase activity were evaluated by real-time PCR. Among the 21 validated genes, the strikingly decreased transcription of PTPRG and AMN1 and increased transcription of UPP1 potentially support data on cell cycle disturbances relevant to cancer, stem cell and neurodegenerative diseases' research. The mapping of interactions of proteins encoded by the validated genes exclusively relied on evidence-based data and revealed broad effects on Wnt pathway members, including WNT3A and DVL3. Intriguingly, the transcription of TERA, a gene of unknown function, is affected by γ-secretase activity and was significantly altered in the analyzed human Alzheimer's disease brain cortices.

Conclusions/Significance

Investigating the effects of γ-secretase activity on gene transcription has revealed several affected clusters of molecular functions and, more specifically, 21 genes that hold significant potential for a better understanding of the biology of γ-secretase and its roles in cancer and Alzheimer's disease pathology.

A genomic scan for age at onset of Alzheimer's disease in 437 families from the NIMH Genetic Initiative

We performed linkage analysis for age at onset (AAO) in the total Alzheimer's disease (AD) NIMH sample (N = 437 families). Families were subset as late-onset (320 families, AAO > or = 65) and early/mixed (117 families, at least 1 member with 50 < AAO < 65). Treating AAO as a censored trait, we obtained the gender and APOE adjusted residuals in a parametric survival model and analyzed the residuals as the quantitative trait (QT) in variance-component linkage analysis. For comparison, AAO-age at exam (AAE) was analyzed as the QT adjusting for affection status, gender, and APOE. Heritabilities for residual and AAO-AAE outcomes were 66.3% and 74.0%, respectively for the total sample, 56.0% and 57.0% in the late-onset sample, and 33.0% for both models in the early/mixed sample. The residual model yielded the largest peaks on chromosome 1 with LOD = 2.0 at 190 cM in the total set, LOD = 1.7 at 116 cM on chromosome 3 in the early/mixed subset, and LOD = 1.4 at 71 and 86 cM, respectively, on chromosome 6 in the late-onset subset. For the AAO-AAE outcome model the largest peaks were identified on chromosome 1 at 137 cM (LOD = 2.8) and chromosome 6 at 69 cM (LOD = 2.3) and 86 cM (LOD = 2.2) all in the late-onset subset. Additional peaks with LOD > or = 1 were identified on chromosomes 1, 2, 3, 6, 8, 9, 10, and 12 for the total sample and each subset. Results replicate previous findings, but identify additional suggestive peaks indicating the genetics of AAO in AD is complex with many chromosomal regions potentially containing modifying genes.

Genetic aspects of Alzheimer disease

Alzheimer disease is the most common cause of dementia and represents a major public health problem. The neuropathologic findings of amyloid-beta plaques and tau containing neurofibrillary tangles represent important molecular clues to the underlying pathogenesis. Genetic factors are well recognized, but complicated. Three rare forms of autosomal-dominant early-onset familial Alzheimer disease have been identified and are associated with mutations in amyloid precursor protein, presenilin 1, and presenilin 2 genes. The more common late-onset form of Alzheimer disease is assumed to be polygenic/multifactorial. However, thus far the only clearly identified genetic risk factor for Alzheimer disease is Apo lipoprotein E. The epsilon4 allele of Apo lipoprotein E influences age at onset of Alzheimer disease, but is neither necessary nor sufficient for the disease. The search continues for the discovery of additional genetic influences.

Further examination of the candidate genes in chromosome 12p13 locus for late-onset Alzheimer disease

A broad region on chromosome 12p13 has been intensely investigated for novel genetic variants associated with Alzheimer disease (AD). We examined this region with 23 microsatellite markers using 124 North European (NE) families and 209 Caribbean Hispanic families with late-onset AD (FAD). Significant evidence for linkage was present in a 5-cM interval near 20 cM in both the NE FAD (LOD = 3.5) and the Caribbean Hispanic FAD (LOD = 2.2) datasets. We further investigated these families and an independent NE case-control dataset using 14 single nucleotide polymorphisms (SNPs). The initial screening of the region at approximately 20 cM in the NE case-control dataset revealed significant association between AD and seven SNPs in several genes, with the strongest result for rs2532500 in TAPBPL (p = 0.006). For rs3741916 in GAPDH, the C allele, rather than the G allele as was observed by Li et al. (Proc Natl Acad Sci U S A 101(44):15688-15693, 2004), was the risk allele. When the two family datasets were examined, none of the SNPs were significant in NE families, but two SNPs were associated with AD in Caribbean Hispanics: rs740850 in NCAPD2 (p = 0.0097) and rs1060620 in GAPDH (p = 0.042). In a separate analysis combining the Caribbean Hispanic families and NE cases and controls, rs740850 was significant after correcting for multiple testing (empirical p = 0.0048). Subsequent haplotype analyses revealed that two haplotype sets-haplotype C-A at SNPs 6-7 within NCAPD2 in Caribbean Hispanics, and haplotypes containing C-A-T at SNPs 8-10 within GAPDH in Caribbean Hispanic family and NE case-control datasets-were associated with AD. Taken together, these SNPs may be in linkage disequilibrium with a pathogenic variant(s) on or near NCAPD2 and GAPDH.

[Risk factors and protective factors of the insanities]

The Alzheimer's disease (AD) is multifactorial. How to explain this group of very heterogeneous factors? Many of them can be considered as biopsychosocial risk factors. In other words, the risk factors, in link with the physiological functioning and a physiopathology, are difficultly dissociable of contingencies of psychological and/or social nature. The vital lead could be the stress bound to these variables, be it biological or psychosocial. It remains to ask the question of the preventive efficiency of treatments to relieve the impact of the traumatizing events of life that entail a depressive state or a state of posttraumatic stress. The hippocamp has to be the object of a quite particular attention. AD is a disease of the adaptation. This integrative model combines three vulnerabilities: a genetic vulnerability which would be there to dictate the type of lesions, their localization and the age of occurence; a psychobiographic vulnerability corresponding to a personality with inadequate mechanisms of defence, precarious adaptability in front of the adversity, weak impact strength and biography built on events of life during childhood, then during the grown-up life of traumatic nature, with a psychosocial environment insufficiently auxiliary; a neuroendocrinologic vulnerability which would base on a deregulation of the corticotrope axis, acquired during its infantile maturation, hampered by too premature stress. It would lead to a bad biological adaptability in stress later, at the origin of the observable lesions in the insanities.

Genetics of Alzheimer's disease: a centennial review

Alzheimer's disease (AD) genetics may be one of the most prolifically published areas in medicine and biology. Three early-onset AD genes with causative mutations (APP, PSEN1, PSEN2) and one late-onset AD susceptibility gene, apolipoprotein E (APOE), exist with ample biologic, genetic, and epidemiologic data. Evidence suggests a significant genetic component underlying AD that is not explained by the known genetic risk factors. This article summarizes the evidence for the genetic component in AD and the identification of the early-onset familial AD genes and APOE, and examines the current state of knowledge about additional AD susceptibility loci and alleles. The future directions for genetic research in AD as a common and complex condition are also discussed.

Common genetic variation within the low-density lipoprotein receptor-related protein 6 and late-onset Alzheimer's disease

Genome-wide linkage studies have defined a broad susceptibility region for late-onset Alzheimer's disease on chromosome 12, which contains the Low-Density Lipoprotein Receptor-Related Protein 6 (LRP6) gene, a coreceptor for Wnt signaling. Here, we report the association between common LRP6 variants and late-onset Alzheimer's disease in a multicenter case-control series as well as in a large family-based series ascertained by the National Institute of Mental Health-National Institute on Aging Genetics Initiative. As shown in the genome-wide linkage studies, our association depends mainly on apolipoprotein E-epsilon4 (APOE-epsilon4) carrier status. Haplotype tagging single-nucleotide polymorphisms (SNPs) with a set of seven allelic variants of LRP6 identified a putative risk haplotype, which includes a highly conserved coding sequence SNP: Ile-1062 --> Val. Functional analyses revealed that the associated allele Val-1062, an allele previously linked to low bone mass, has decreased beta-catenin signaling in HEK293T cells. Our study unveils a genetic relationship between LRP6 and APOE and supports the hypothesis that altered Wnt/beta-catenin signaling may be involved in this neurodegenerative disease.

The neuronal sortilin-related receptor SORL1 is genetically associated with Alzheimer disease

The recycling of the amyloid precursor protein (APP) from the cell surface via the endocytic pathways plays a key role in the generation of amyloid beta peptide (Abeta) in Alzheimer disease. We report here that inherited variants in the SORL1 neuronal sorting receptor are associated with late-onset Alzheimer disease. These variants, which occur in at least two different clusters of intronic sequences within the SORL1 gene (also known as LR11 or SORLA) may regulate tissue-specific expression of SORL1. We also show that SORL1 directs trafficking of APP into recycling pathways and that when SORL1 is underexpressed, APP is sorted into Abeta-generating compartments. These data suggest that inherited or acquired changes in SORL1 expression or function are mechanistically involved in causing Alzheimer disease.

The ups and downs of Wnt signaling in prevalent neurological disorders

In order to function properly, the brain must be wired correctly during critical periods in early development. Mistakes in this process are hypothesized to occur in disorders like autism and schizophrenia. Later in life, signaling pathways are essential in maintaining proper communication between neuronal and non-neuronal cells, and disrupting this balance may result in disorders like Alzheimer's disease. The Wnt/beta-catenin pathway has a well-established role in cancer. Here, we review recent evidence showing the involvement of Wnt/beta-catenin signaling in neurodevelopment as well as in neurodegenerative diseases. We suggest that the onset/development of such pathological conditions may involve the additive effect of genetic variation within Wnt signaling components and of molecules that modulate the activity of this signaling cascade.

Parsing the genetic heterogeneity of chromosome 12q susceptibility genes for Alzheimer disease by family-based association analysis

Previous linkage studies have suggested that chromosome 12 may harbor susceptibility genes for late-onset Alzheimer disease (LOAD). No risk genes on chromosome 12 have been conclusively identified yet. We have reported that the linkage evidence for LOAD in a 12q region was significantly increased in autopsy-confirmed families particularly for those showing no linkage to alpha-T catenin gene, a LOAD candidate gene on chromosome 10 [LOD score increased from 0.1 in the autopsy-confirmed subset to 4.19 in the unlinked subset (optimal subset); p<0.0001 for the increase in LOD score], indicating a one-LOD support interval spanning 6 Mb. To further investigate this finding and to identify potential candidate LOAD risk genes for follow-up analysis, we analyzed 99 single nucleotide polymorphisms in this region, for the overall sample, the autopsy-confirmed subset, and the optimal subset, respectively, for comparison. We saw no significant association (p<0.01) in the overall sample. In the autopsy-confirmed subset, the best finding was obtained in the activation transcription factor 7 (ATF7) gene (single-locus association, p=0.002; haplotype association global, p=0.007). In the optimal subset, the best finding was obtained in the hypothetical protein FLJ20436 (FLJ20436) gene (single-locus association, p=0.0026). These results suggest that subset and covariate analyses may be one approach to help identify novel susceptibility genes on chromosome 12q for LOAD.

A genome-wide linkage analysis of dementia in the Amish

Susceptibility genes for Alzheimer's disease are proving to be highly challenging to detect and verify. Population heterogeneity may be a significant confounding factor contributing to this difficulty. To increase the power for disease susceptibility gene detection, we conducted a genome-wide genetic linkage screen using individuals from the relatively isolated, genetically homogeneous, Amish population. Our genome linkage analysis used a 407-microsatellite-marker map (average density 7 cM) to search for autosomal genes linked to dementia in five Amish families from four Midwestern U.S. counties. Our highest two-point lod score (3.01) was observed at marker D4S1548 on chromosome 4q31. Five other regions (10q22, 3q28, 11p13, 4q28, 19p13) also demonstrated suggestive linkage with markers having two-point lod scores >2.0. While two of these regions are novel (4q31 and 11p13), the other regions lie close to regions identified in previous genome scans in other populations. Our results identify regions of the genome that may harbor genes involved in a subset of dementia patients, in particular the North American Amish community.

Combinatorial Mismatch Scan (CMS) for loci associated with dementia in the Amish

BACKGROUND

Population heterogeneity may be a significant confounding factor hampering detection and verification of late onset Alzheimer's disease (LOAD) susceptibility genes. The Amish communities located in Indiana and Ohio are relatively isolated populations that may have increased power to detect disease susceptibility genes.

METHODS

We recently performed a genome scan of dementia in this population that detected several potential loci. However, analyses of these data are complicated by the highly consanguineous nature of these Amish pedigrees. Therefore we applied the Combinatorial Mismatch Scanning (CMS) method that compares identity by state (IBS) (under the presumption of identity by descent (IBD)) sharing in distantly related individuals from such populations where standard linkage and association analyses are difficult to implement. CMS compares allele sharing between individuals in affected and unaffected groups from founder populations. Comparisons between cases and controls were done using two Fisher's exact tests, one testing for excess in IBS allele frequency and the other testing for excess in IBS genotype frequency for 407 microsatellite markers.

RESULTS

In all, 13 dementia cases and 14 normal controls were identified who were not related at least through the grandparental generation. The examination of allele frequencies identified 24 markers (6%) nominally (p < or = 0.05) associated with dementia; the most interesting (empiric p < or = 0.005) markers were D3S1262, D5S211, and D19S1165. The examination of genotype frequencies identified 21 markers (5%) nominally (p < or = 0.05) associated with dementia; the most significant markers were both located on chromosome 5 (D5S1480 and D5S211). Notably, one of these markers (D5S211) demonstrated differences (empiric p < or = 0.005) under both tests.

CONCLUSION

Our results provide the initial groundwork for identifying genes involved in late-onset Alzheimer's disease within the Amish community. Genes identified within this isolated population will likely play a role in a subset of late-onset AD cases across more general populations. Regions highlighted by markers demonstrating suggestive allelic and/or genotypic differences will be the focus of more detailed examination to characterize their involvement in dementia.

Protective effect of Rosa laevigata against amyloid beta peptide-induced oxidative stress

The amyloid beta (Abeta) peptide is known to increase free radical production in nerve cells, leading to cell death. To investigate the effect of Rosa laevigata against Abeta-induced oxidative damage, in vitro assays and in vivo behavioral tests were performed. R. laevigata showed cell protective effects against oxidative stress-induced cytotoxicity. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) reduction assay exhibited significant increase in cell viability when rat pheochromocytoma (PC 12) cells were treated with R. laevigata extracts. Administration of R. laevigata extracts to mice significantly reversed the Abeta-induced learning and memory impairment in in vivo behavioral tests. These results suggest that R. laevigata extracts can reduce the cytotoxicity of Abeta in PC 12 cells, possibly by the reduction of oxidative stress, and these extracts may be useful in the prevention of Alzheimer's disease.

Retinoid receptors, transporters, and metabolizers as therapeutic targets in late onset Alzheimer disease

Vitamin A (retinoid) is required in the adult brain to enable cognition, learning, and memory. While brain levels of retinoid diminish over the course of normal ageing, retinoid deficit is greater in late onset Alzheimer disease (LOAD) brains than in normal-aged controls. This paper reviews recent evidence supporting these statements and further suggests that genes necessary for the synthesis, transport and function of retinoid to and within the ageing brain are appropriate targets for treatment of LOAD. These genes tend to be clustered with genes that have been proposed as candidates in LOAD, are found at chromosomal regions linked to LOAD, and suggest the possibility of an overall coordinated regulation. This phenomenon is termed Chromeron and is analogous to the operon mechanism observed in prokaryotes. Suggested treatment targets are the retinoic-acid inactivating enzymes (CYP26)s, the retinol binding and transport proteins, retinol-binding protein (RBP)4 and transthyretin (TTR), and the retinoid receptors. TTR as a LOAD target is the subject of active investigation. The retinoid receptors and the retinoid-inactivating enzymes have previously been proposed as targets. This is the first report to suggest that RBP4 is an amenable treatment target in LOAD. RBP4 is elevated in type-2 diabetes and obesity, conditions associated with increased risk for LOAD. Fenretinide, a novel synthetic retinoic acid (RA) analog lowers RBP4 in glucose intolerant obese mice. The feasibility of using fenretinide either as an adjunct to present LOAD therapies, or on its own as an early prevention strategy should be determined.

A scan of chromosome 10 identifies a novel locus showing strong association with late-onset Alzheimer disease

Strong evidence of linkage to late-onset Alzheimer disease (LOAD) has been observed on chromosome 10, which implicates a wide region and at least one disease-susceptibility locus. Although significant associations with several biological candidate genes on chromosome 10 have been reported, these findings have not been consistently replicated, and they remain controversial. We performed a chromosome 10-specific association study with 1,412 gene-based single-nucleotide polymorphisms (SNPs), to identify susceptibility genes for developing LOAD. The scan included SNPs in 677 of 1,270 known or predicted genes; each gene contained one or more markers, about half (48%) of which represented putative functional mutations. In general, the initial testing was performed in a white case-control sample from the St. Louis area, with 419 LOAD cases and 377 age-matched controls. Markers that showed significant association in the exploratory analysis were followed up in several other white case-control sample sets to confirm the initial association. Of the 1,397 markers tested in the exploratory sample, 69 reached significance (P < .05). Five of these markers replicated at P < .05 in the validation sample sets. One marker, rs498055, located in a gene homologous to RPS3A (LOC439999), was significantly associated with Alzheimer disease in four of six case-control series, with an allelic P value of .0001 for a meta-analysis of all six samples. One of the case-control samples with significant association to rs498055 was derived from the linkage sample (P = .0165). These results indicate that variants in the RPS3A homologue are associated with LOAD and implicate this gene, adjacent genes, or other functional variants (e.g., noncoding RNAs) in the pathogenesis of this disorder.

A 3'-UTR polymorphism in the oxidized LDL receptor 1 gene increases Abeta40 load as cerebral amyloid angiopathy in Alzheimer's disease

It is presently unclear whether polymorphic variations in the oxidized low-density lipoprotein receptor 1 (OLR1), or low-density lipoprotein receptor-related protein 1 (LRP1), genes act as risk factors for Alzheimer's disease (AD). In the present study, we have investigated the extent of amyloid beta protein (Abeta) deposition as cerebral amyloid angiopathy (CAA) or senile plaques (SP) in relationship to OLR1 +1071 and +1073 polymorphisms and LRP1 C766T polymorphism in patients with AD There was an increased Abeta40 load as CAA, but not as SP, in frontal cortex of AD patients carrying OLR1+1073 CC genotype, compared to those with CT, TT or CT+TT genotypes, but only in those individuals without apolipoprotein (APOE) epsilon4 allele. No differences in total Abeta or Abeta42 load as CAA or SP between OLR1+1073 genotypes was seen, nor were there any differences between OLR1+1071 and LRP1 genotypes for any measure of Abeta. Present data suggests that homozygosity for the C allele for OLR1+1073 polymorphism, selectively in individuals without APOE epsilon4 allele, may impair clearance of Abeta, and particularly Abeta40, from the brain across the blood-brain barrier, leading to its 'diversion' into perivascular drainage channels, thereby increasing the severity of CAA in such persons.

Candidate genes for late-onset Alzheimer's disease: Focus on chromosome 12

In recent years, there was an increasing interest on candidate genes may play an important role in the development of Alzheimer's disease (AD). Several genome wide screens have undertaken so far or expanded recently, and suggested a number of genomic areas that may contain novel susceptibility genes for AD, in particular most compelling have been the findings on chromosome 12. Polymorphisms in different susceptibility genes on chromosome 12 (A2M, LRP1, CP2 and OLR1) are now being suggested as possible genetic markers for increased risk of developing AD. However, many of these studies are controversial and have shown conflicting results. Thus far, the search for the chromosome 12 Alzheimer's gene must continue and there are several other genes in this region that we are looking at. In this article, we focused on the current knowledge of the genetics of familial late-onset and sporadic AD linked to the chromosome 12, and the future search for other candidate genes.

Association study of the A2M and LRP1 Genes with Alzheimer disease in the Han Chinese

BACKGROUND

Low-density lipoprotein receptor-related protein 1 (LRP1) and alpha-2-macroglobulin (A2M) are two plausible candidate genes for Alzheimer disease (AD) based on their important biological function and positional information. To date, numerous studies have investigated their possible association with AD but the results are controversial.

METHODS

To investigate the potential genetic contribution of the two genes in the Han Chinese population, we performed a case-control association study using 10 polymorphisms (4 in LRP1 and 6 in A2M) that span approximately the whole corresponding gene.

RESULTS

Comparison of allele, genotype, and haplotype frequencies for polymorphisms in A2M revealed no significant differences between patients and control subjects. For the LRP1 gene, however, we found an overrepresentation of the CTCG haplotype in the control group (p = .002). The difference was still of statistical significance in the apolipoprotein E (APOE) epsilon 4 negative subjects (p(CTCG) = .003). Multiple logistic regression analysis did not show any evidence of synergism between A2M, LRP1, and APOE.

CONCLUSIONS

Our results indicate that the CTCG haplotype of LRP1 may reduce the risk of late-onset AD, but A2M is not associated with this disease in the Han Chinese population.

Current knowledge of chromosome 12 susceptibility genes for late-onset Alzheimer's disease

In the last decade, it has become more apparent the important role genes play in the development of late-onset Alzheimer's disease (AD). Great efforts, involving human genome scans and candidate gene studies, have been given towards identifying susceptibility genes for AD. A number of regions on different chromosomes have been reported to demonstrate linkage for AD. Of these, findings on chromosome 12 are some of the most compelling. Worldwide genetic association studies pre-dating and subsequent to recent linkage studies have identified and focused upon a number of genes that map to the areas of reported linkage on chromosome 12, however, analyses of those genes studied to date, on the whole, remain inconclusive and ambiguous. This paper reviews studies that have provided evidence of linkage for AD on chromosome 12 and in turn discusses the work conducted to date on candidate genes that have been identified and map to the chromosome 12 regions of interest.

An autosomal genomic screen for dementia in an extended Amish family

Apolipoprotein E (APOE) is the only universally confirmed susceptibility gene for late-onset Alzheimer disease (LOAD), although many loci are believed to modulate LOAD risk. The genetic homogeneity of isolated populations, such as the Amish, potentially provide increased power to identify LOAD susceptibility genes. Population homogeneity in these special populations may reduce the total number of susceptibility genes contributing to the complex disorder, thereby increasing the ability to identify any one susceptibility gene. Dementia in the Amish is clinically indistinguishable from LOAD in the general population. Previous studies in the Amish demonstrated a significantly decreased frequency of the APOE-4 susceptibility allele, but significant familial clustering of dementia [M.A. Pericak-Vance, C.C. Johnson, J.B. Rimmler, A.M. Saunders, L.C. Robinson, E.G. D'Hondt, C.E. Jackson, J.L. Haines, Alzheimer's disease and apolipoprotein E-4 allele in an Amish population, Ann. Neurol. 39 (1996) 700-704]. These data suggested that a genetic etiology independent of APOE may underlie the dementia observed in this population. In the present analysis, we focused on a large, multiplex, inbred Amish family (24 sampled individuals; 10 of whom are affected). We completed a genomic screen to identify novel LOAD loci (n=316 genetic markers), using both model-dependent "affecteds-only" analysis (dominant and recessive) and model-independent affected relative pair analysis. Interesting results (lod>1.5 or p<0.01) were obtained for markers on eight chromosomes (2q, 5q, 6q, 7p, 8p, 8q, 11p, 18p, 18q, and 19q). The highest overall score was a multipoint lod score of 3.1 on chromosome 11p. Most regions we identified were not previously detected by genomic screens of outbred populations and may represent population-specific susceptibilities to LOAD. These loci are currently under further investigation in a study of LOAD including additional Amish families.

Polymorphisms in the oxidized low-density lipoprotein receptor-1 gene and risk of Alzheimer's disease

The +1073 C/T polymorphism of the oxidized low-density lipoprotein receptor-1 (OLR1) gene has been reported to be associated with late-onset Alzheimer's disease, whereas for the +1071 T/A polymorphism no association was found. We genotyped 169 sporadic Alzheimer's disease patients and 264 sex- and age-matched nondemented controls from Southern Italy for OLR1 +1073 C/T and +1071 T/A polymorphisms and for apolipoprotein E and LBP-1c/CP2/LSF. We also performed haplotype analysis. For the +1073 C/T polymorphism, the C allele and the CC genotype have been associated with a higher risk for Alzheimer's disease without apolipoprotein E or CP2 interaction. The two polymorphisms were in linkage disequilibrium, with the haplotype T-C at significant increased risk of developing Alzheimer's disease in the whole sample and in elderly persons 70 years or older. In our population, the +1073 C/T OLR1 polymorphism exhibited a significant association with Alzheimer's disease, further supporting the role of OLR1 as a candidate risk gene for sporadic Alzheimer's disease.

Genome screen for loci influencing age at onset and rate of decline in late onset Alzheimer's disease

We performed an affected sib-pair (ASP) linkage analysis to test for the effects of age at onset (AAO), rate of decline (ROD), and Apolipoprotein E (APOE) genotype on linkage to late-onset Alzheimer's disease (AD) in a sample comprising 428 sib-pairs. We observed linkage of mean AAO to chromosome 21 in the whole sample (max LOD = 2.57). This came entirely from the NIMH sample (max LOD = 3.62), and was strongest in pairs with high mean AAO (>80). A similar effect was observed on chromosome 2q in the NIMH sample (max LOD = 2.73); this region was not typed in the IADC/UK sample. Suggestive evidence was observed in the combined sample of linkage of AAO difference to chromosome 19q (max LOD = 2.33) in the vicinity of APOE and 12p (max LOD = 2.22), with linkage strongest in sib-pairs with similar AAO. Mean ROD showed suggestive evidence of linkage to chromosome 9q in the whole sample (max LOD = 2.29), with the effect strongest in the NIMH sample (max LOD = 3.58), and in pairs with high mean ROD. Additional suggestive evidence was also observed in the NIMH sample with AAO difference on chromosome 6p (max LOD = 2.44) and 15p (max LOD = 1.87), with linkage strongest in pairs with similar AAO, and in the UK sample with mean ROD on chromosome 1p (max LOD = 2.73, linkage strongest in pairs with high mean ROD). We also observed suggestive evidence of increased identical by descent (IBD) in APOE epsilon4 homozygotes on chromosome 1 (max LOD = 3.08) and chromosome 9 (max LOD = 3.34). The previously reported genome-wide linkage of AD to chromosome 10 was not influenced by any of the covariates studied.

Molecular biology and genetics of Alzheimer's disease

Like several other adult onset neurodegenerative diseases, Alzheimer's disease is a multifactorial illness with both genetic and non-genetic causes. Recent genetic studies have identified four genes associated with inherited risk for AD (presenilin 1, presenilin 2, amyloid precursor protein, and apolipoprotein E). These genes account for about half of the total genetic risk for Alzheimer's disease. It is suspected that several other Alzheimer's disease-susceptibility genes exist, and their identification is the subject of ongoing research. Nevertheless, biological studies on the effects of mutations in the four known genes has led to the conclusion that all of these genes cause dysregulation of amyloid precursor protein processing and in particular dysregulation of the handling of a proteolytic derivative termed Abeta. The accumulation of Abeta appears to be an early and initiating event that triggers a series of downstream processes including misprocessing of the tau protein. This cascade ultimately causes neuronal dysfunction and death, and leads to the clinical and pathological features of Alzheimer's disease. Knowledge of this biochemical cascade now provides several potential targets for the development of diagnostics and therapeutics.

Candidate gene association study of solute carrier family 11a members 1 (SLC11A1) and 2 (SLC11A2) genes in Alzheimer's disease

Divalent cations are strongly implicated in Alzheimer's disease (AD) pathogenesis, and can regulate amyloid beta-peptide aggregation. The proton-divalent cation transporters encoded by SLC11A1 (formerly NRAMP1) on chromosome 2q35, and SLC11A2 (also known as DCT1 and DMT1) on chromosome 12q13, are expressed in the brain and regulate ion homeostasis from endosomal compartments. SLC11A1 also has pleiotropic effects on pro-inflammatory responses that may be important in AD. We analyzed seven informative polymorphisms in the SLC11A1 and SLC11A2 genes encoding these divalent cation transporters in a sample of 216 late-onset AD cases and 323 age-matched controls. We found only borderline evidence (p=0.08) for an allelic association between SNP rs407135 at SLC11A2 and AD, in which the variant allele was protective (odd ratio (OR) 0.77; 95% CI 0.56-1.04) relative to the more common allele. There was no interaction with apolipoprotein E (APOE) varepsilon4, but stratification by gender showed that all of the effect of SLC11A2 was in the male patient group. No other associations with AD were observed at SLC11A1 or SLC11A2, indicating no major effect of either gene for the occurrence of AD.

Cholesterol at the crossroads: Alzheimer's disease and lipid metabolism

Alzheimer's Disease (AD) is a devastating disease that affects millions of elderly persons. Despite years of intense investigations, genetic risk factors that affect the majority of AD cases have yet to be determined. Recent studies suggest that cholesterol metabolism has integral part in AD pathogenesis, suggesting that genes that regulate lipid metabolism may also play roles in AD. This review will first describe emerging evidence that links cholesterol to the mechanisms thought to underlie AD. Based on this rationale, candidate genes located in regions implicated in AD that have roles in lipid metabolism will then be discussed.

Fine mapping of 10q and 18q for familial Alzheimer's disease in Caribbean Hispanics

Familial Alzheimer's disease (AD [MIM 104300]) has been a focus of intense investigation, primarily in Caucasian families from Europe and North America families. Although the late-onset form of familial AD, beginning after age 65 years, has been linked to regions on chromosomes 10q and 12p, the specific genetic variants have not yet been consistently identified. Using a unique cohort of families of Caribbean Hispanics ancestry, we screened the genome using 340 markers on 490 family members from 96 families with predominantly late-onset AD. We observed the strongest support for linkage on 18q (LOD=3.14). However, 17 additional markers (chromosomes 1-6, 8, 10, 12, and 14) exceeded a two-point LOD score of 1.0 under the affecteds-only autosomal dominant model or affected sibpair model. As we previously reported the fine-mapping effort on 12p showing modest evidence of linkage, we focused our fine-mapping efforts on two other candidate regions in the current report, namely 10q and 18q. We added 31 family members and eight additional Caribbean Hispanic families to fine map 10q and 18q. With additional microsatellite markers, the evidence for linkage for 18q strengthened near 112 cM, where the two-point LOD score for D18S541 was 3.37 and the highest NPL score in that region was 3.65 (P=0.000177). This narrow region contains a small number of genes expressed in the brain. However, at 10q (134-138 cM), the NPL score decreased from 3.15 (P=0.000486) to 2.1 (P=0.0218), but two broad peaks remained overlapping with previously reported peaks. Our results provide modest support for linkage on 10q and 12p in this cohort of Caribbean Hispanic families with familial Alzheimer's disease, and strong evidence for a new locus on 18q.

Association of late-onset Alzheimer's disease with genetic variation in multiple members of the GAPD gene family

Although several genes have been implicated in the development of the early-onset autosomal dominant form of Alzheimer's disease (AD), the genetics of late-onset AD (LOAD) is complex. Loci on several chromosomes have been linked to the disease, but so far only the apolipoprotein E gene has been consistently shown to be a risk factor. We have performed a large-scale single-nucleotide polymorphism (SNP)-based association study, across the region of linkage on chromosome 12, in multiple case-control series totaling 1,089 LOAD patients and 1,196 control subjects and report association with SNPs in the glyceraldehyde-3-phosphate dehydrogenase (GAPD) gene. Subsequent analysis of GAPD paralogs on other chromosomes demonstrated association with two other paralogs. A significant association between LOAD and a compound genotype of the three GAPD genes was observed in all three sample sets. Individually, these SNPs make differential contributions to disease risk in each of the casecontrol series, suggesting that variants in functionally similar genes may account for series-to-series heterogeneity of disease risk. Our observations raise the possibility that GAPD genes are AD risk factors, a hypothesis that is consistent with the role of GAPD in neuronal apoptosis.

Molecular Genetics of Late-Onset Alzheimer's Disease

Late-onset Alzheimer's disease (AD) is a complex and multifactorial disease with the possible involvement of several genes. Apolipoprotein E (APOE), especially the APOE*4 allele, has been established as a strong susceptibility marker that accounts for nearly 30% of the risk in late-onset AD. However, as the APOE*4 allele is neither necessary nor sufficient for the development of AD, it emphasizes the involvement of other genetic and/or environmental factors which, alone or in conjunction with APOE*4, can modify the risk of AD. Recently, genome-wide linkage or linkage disequilibrium studies on late-onset AD have provided informative data for the existence of multiple putative genes for AD on several chromosomes, with the strongest evidence on chromosomes 12, 10, 9 and 6. This paper attempts to review the current progress on the identification of additional genetic loci for late-onset AD.

Familial clustering and genetic risk for dementia in a genetically isolated Dutch population

Despite advances in elucidating the genetic epidemiology of Alzheimer's disease and frontotemporal dementia, the aetiology for most patients with dementia remains unclear. We examined the genetic epidemiology of dementia in a recent genetically isolated Dutch population founded around 1750. The series of 191 patients ascertained comprised 122 probable Alzheimer's disease patients with late onset and 17 with early onset, and 22 with possible Alzheimer's disease. It further included 10 patients with vascular dementia, nine with Lewy body dementia and six with frontotemporal dementia. All patients, except those with vascular dementia, were more closely related than healthy individuals from the same area. Clustering was strongest for patients with early-onset Alzheimer's disease or Lewy body dementia. Although 14% of late-onset Alzheimer's disease patients had evidence of autosomal dominant disease, consanguinity was found in three late-onset Alzheimer's disease patients, suggesting a recessive or polygenic model underlying the trait. We found no clustering of vascular dementia, implying a difference in genetic risk for late-onset Alzheimer's disease and vascular dementia. Mutations in known genes could not explain the occurrence of dementia, but the population attributable proportion of apolipoprotein E gene (APOE*4) was high (45%) due to a high frequency of APOE*4 carriers. Earlier identified regions on chromosomes 10 and 12, nor the effect of the alpha-2-macroglobulin (A2M) I/D polymorphism on Alzheimer's disease could be confirmed in our study. We did find evidence for association between the A2M D-allele and Lewy body dementia. Our data showed a strong familial clustering of various forms of dementia in this isolated Dutch population. A high percentage of late-onset Alzheimer's disease could be explained by APOE*4, but 55% of its origin is still unknown.

Molecular genetics of Alzheimer's disease

Alzheimer disease (AD) is the most common cause of dementia. In the past decade, many advances in the understanding of the etiology of AD have been reported. Familial early onset AD is a heterogeneous disorder that can be caused by mutations in at least three different genes. Current studies are focused on identifying genetic risk factors for late onset AD. In this article, the authors will review the progress in understanding the pathogenic implications of the genes mutated in familial early onset AD and the mapping studies to identify additional genes involved in late-onset AD.

Evidence of linkage and association on chromosome 20 for late-onset Alzheimer disease

Recently, we reported evidence of linkage on chromosome 20 for Alzheimer disease (AD) using a novel statistical approach to incorporate covariates (e.g., age, ApoE genotype) into the analysis. These results suggest that very elderly subjects (>85 years), and individuals who carry an epsilon2 allele at the ApoE locus are more likely to be linked to this candidate region. The region on chromosome 20 includes a strong candidate gene, cystatin C (CST3), which has previously been associated with AD in case-control studies. We investigated these findings further by genotyping additional markers to narrow the candidate region, and to identify evidence of linkage disequilibrium as additional support for a susceptibility locus on chromosome 20. We selected 43 elderly sibships (89 subjects) from the NIMH AD Genetics Initiative based on current age older than 84 years, and identified 129 unrelated control subjects who were older than 84 years from the Oregon Brain Aging Study to conduct linkage and association studies in this region. Fourteen additional markers were evaluated, including 4 markers located within or near CST3. We narrowed the candidate region on chromosome 20 to an 11.8-cM region between markers D20S174 and D20S471, which includes the CST3 candidate gene. In addition, we observed evidence of association for markers located near the CST3 candidate gene, with P values between 0.002 and 0.08 for two-locus haplotypes. These results support the presence of a susceptibility locus for AD in the vicinity of CST3 for very elderly subjects with AD.

Genetic and environmental epidemiology of Alzheimer's disease in arabs residing in Israel

We have found an unusually high prevalence of Alzheimer's disease (AD) in Wadi Ara, an inbred Arab community in northern Israel. Allele frequencies of 4.5% and 3.5% were found for the apolipoprotein E e4 allele among AD cases and nondemented controls, respectively, showing that other genetic or environmental influences must be responsible. Family studies revealed that more than one-third of the AD cases are members of one hamula (tribal group) within Wadi Ara. We hypothesize that the high risk of AD in this genetic isolate may be attributable to a founder effect enhanced by consanguinity. It is also possible that smoking or high fat diet are responsible. To map chromosomal loci contributing to AD susceptibility, we conducted a genome scan from specific hamulas and followed candidate regions found to be linked to disease. Markers from 18 chromosomal regions showed significant allelic association with AD. Smoking was very common in men but was not linked to the presence of AD in Wadi Ara, The unique characteristics of this community, together with the large amount of human genome data, should allow for the identification of AD genes in candidate regions.

Epidemiology of neurodegeneration

Alzheimer's disease, Parkinson's disease, and motor neuron disease share a propensity to occur with increasing age and as either a sporadic or a familial disorder. A number of behavioral and environmental risk factors have been proposed for each disorder, but most associations lack consistency and specificity. Over the last decade the remarkable frequency of these disorders has become apparent, and the identification of mutations in genes has provided the means to understand their pathogenesis. Better and more accurate means to characterize and diagnose these diseases has greatly facilitated analytic epidemiology. The analysis of behavioral and genetic factors that may lower disease risk has led to clinical trials that are either in progress or being planned with the aim of preventing these disorders.

The Genetics of Adult-Onset Neuropsychiatric Disease: Complexities and Conundra?

Genetic factors play a major role in the etiology of adult-onset neurodegenerative and neuropsychiatric disorders. Several highly penetrant genes have been cloned for rare, autosomal-dominant, early-onset forms of neurodegenerative diseases. These genes have provided important insights into the mechanisms of these diseases (often altering neuronal protein processing). However, the genes associated with inherited susceptibility to late-onset neurodegenerative diseases, schizophrenia, and bipolar disorder appear to have smaller effects and are likely to interact with each other (and with nongenetic factors) to modulate susceptibility and/or disease phenotype. Several strategies have recently been applied to address this complexity, leading to the identification of a number of candidate susceptibility loci/genes.

Association of 3'-UTR polymorphisms of the oxidised LDL receptor 1 (OLR1) gene with Alzheimer's disease

Although possession of the epsilon 4 allele of the apolipoprotein E gene appears to be an important biological marker for Alzheimer's disease (AD) susceptibility, strong evidence indicates that at least one additional risk gene exists on chromosome 12. Here, we describe an association of the 3'-UTR +1073 C/T polymorphism of the OLR1 (oxidised LDL receptor 1) on chromosome 12 with AD in French sporadic (589 cases and 663 controls) and American familial (230 affected sibs and 143 unaffected sibs) populations. The age and sex adjusted odds ratio between the CC+CT genotypes versus the TT genotypes was 1.56 (p=0.001) in the French sample and 1.92 (p=0.02) in the American sample. Furthermore, we have discovered a new T/A polymorphism two bases upstream of the +1073 C/T polymorphism. This +1071 T/A polymorphism was not associated with the disease, although it may weakly modulate the impact of the +1073 C/T polymorphism. Using 3'-UTR sequence probes, we have observed specific DNA protein binding with nuclear proteins from lymphocyte, astrocytoma, and neuroblastoma cell lines, but not from the microglia cell line. This binding was modified by both the +1071 T/A and +1073 C/T polymorphisms. In addition, a trend was observed between the presence or absence of the +1073 C allele and the level of astrocytic activation in the brain of AD cases. However, Abeta(40), Abeta(42), Abeta total, and Tau loads or the level of microglial cell activation were not modulated by the 3'-UTR OLR1 polymorphisms. Finally, we assessed the impact of these polymorphisms on the level of OLR1 expression in lymphocytes from AD cases compared with controls. The OLR1 expression was significantly lower in AD cases bearing the CC and CT genotypes compared with controls with the same genotypes. In conclusion, our data suggest that genetic variation in the OLR1 gene may modify the risk of AD.

Lewy body pathology is a frequent co-pathology in familial Alzheimer's disease

Our institution is currently engaged in ongoing genetic studies of familial Alzheimer's disease (AD), which include clinical ascertainment and brain autopsy of both affected and non-affected family members. Here we describe the analysis of 22 AD families, each with at least one family member with a postmortem diagnosis of dementia with Lewy bodies (DLB). For this study, 47 brains were examined according to NINCDS-Reagan Institute criteria for the diagnosis of AD. Lewy body pathology was evaluated with alpha-synuclein immunohistochemistry. Four families, with either one or two autopsies showing Lewy body pathology, demonstrated linkage to 12p. Five families had two or more autopsies with Lewy body pathology, but their linkage status was unknown. The remaining 13 families had one autopsy demonstrating Lewy bodies. These findings suggest that at least one pathological form of DLB may be familial. In some families, the pathological phenotype is identical in all examined affected family members; but in others, there may be several pathologies that coexist. Careful neuropathological examination of affected family members may prove critical for future genetic analysis of AD and DLB.

Evidence for defective retinoid transport and function in late onset Alzheimer's disease

The hypothesis of this article is that late onset Alzheimer's disease (AD) is influenced by the availability in brain of retinoic acid (RA), the final product of the vitamin A (retinoid) metabolic cascade. Genetic, metabolic, and environmental/dietary evidence is cited supporting this hypothesis. Significant genetic linkages to AD are demonstrated for markers close to four of the six RA receptors, RA receptor G at 12q13, retinoid X receptor B at 6p21.3, retinoid X receptor G at 1q21, and RA receptor A at 17q21. Three of the four retinol-binding proteins at 3q23 and 10q23 and the RA-degrading cytochrome P450 enzymes at 10q23 and 2p13 map to AD linkages. Synthesis of the evidence supports retinoid hypofunction and impaired transport as contributing factors. These findings suggest testable experiments to determine whether increasing the availability of retinoid in brain, possibly through pharmacologic targeting of the RA receptors and the cytochrome P450 RA-inactivating enzymes, can prevent or decrease amyloid plaque formation.