Biomarkers and Risk Factors of Dementia

Dementia is a devastating disease that is common in elderly people. The prevalence increases from almost 1% at age 65 to over 40% of people older than 90 years.1 Because the population is aging, the number of people living with dementia world- wide is expected to double every 20 years with an expected number of 81 million people with dementia in 2040.2 Currently, dementia is still a clinical diagnosis of disturbances in cognitive functions that interfere with normal daily functioning.3,4 The major subtype of dementia is Alzheimer disease, which based on a clinical diag- nosis, accounts for around 70% of all dementia. The second most common subtype is vascular dementia, which is diagnosed in about 15% of dementia cases.1 Nowadays, however, we know that most patients with dementia have a mix of the neurodegen- erative changes that typically occur in Alzheimer disease, vascular pathology and other pathological signs, like Lewy bodies.5,6 In addition, vascular risk factors have repeatedly been associated with not only vascular dementia, but also with Alzheim- er disease,7 supporting the neuropathological findings of mixed brain pathologies. Although many risk factors for dementia have been identified in the past decades, the exact mechanisms that lead to dementia are still unclear. When the clinical di- agnosis of dementia is made, the actual neuropathological processes that have lead to dementia have already been ongoing for many years. Biomarkers that can detect these processes before a clinical diagnosis can be made are strongly needed in order to identify persons who will develop dementia, to gain more insight in the pathogen- esis of dementia and ultimately to help find new therapeutic agents that may alter or stop the disease. Currently, the most explored biomarkers are imaging markers and the proteins β-Amyloid (Aβ)-42 and tau that are altered in the cerebrospinal fluid of patients with Alzheimer disease early in the disease process.8,9 A lumbar puncture, required to obtain cerebrospinal fluid, is a relative invasive procedure that is not easily performed on large numbers of patients or in the general population, and imaging methods such as PET are not routinely available in all clinical settings. Less invasive biomarkers of dementia are therefore wanted

Genome-wide haplotype association study identifies the FRMD4A gene as a risk locus for Alzheimer's disease

Recently, several genome-wide association studies (GWASs) have led to the discovery of nine new loci of genetic susceptibility in Alzheimer's disease (AD). However, the landscape of the AD genetic susceptibility is far away to be complete and in addition to single-SNP (single-nucleotide polymorphism) analyses as performed in conventional GWAS, complementary strategies need to be applied to overcome limitations inherent to this type of approaches. We performed a genome-wide haplotype association (GWHA) study in the EADI1 study (n=2025 AD cases and 5328 controls) by applying a sliding-windows approach. After exclusion of loci already known to be involved in AD (APOE, BIN1 and CR1), 91 regions with suggestive haplotype effects were identified. In a second step, we attempted to replicate the best suggestive haplotype associations in the GERAD1 consortium (2820 AD cases and 6356 controls) and observed that 9 of them showed nominal association. In a third step, we tested relevant haplotype associations in a combined analysis of five additional case-control studies (5093 AD cases and 4061 controls). We consistently replicated the association of a haplotype within FRMD4A on Chr.10p13 in all the data set analyzed (OR: 1.68; 95% CI: (1.43-1.96); P=1.1 × 10 -10). We finally searched for association between SNPs within the FRMD4A locus and Aβ plasma concentrations in three independent non-demented populations (n=2579). We reported that polymorphisms were associated with plasma Aβ42/Aβ40 ratio (best signal, P=5.4 × 10 -7). In conclusion, combining both GWHA study and a conservative three-stage replication approach, we characterised FRMD4A as a new genetic risk factor of AD

Insulin metabolism and the risk of Alzheimer disease: The Rotterdam Study

Objective: Diabetes mellitus has been associated with an increased risk of Alzheimer disease (AD), but how it exerts its effect remains controversial. Possible pathophysiologic mechanisms are glucose toxicity and a direct effect of insulin on amyloid metabolism. Most studies had short follow-up, and longer-term effects of diabetes on AD risk are unknown. We investigated whether fasting glucose and insulin levels and insulin resistance are associated with the risk of AD and whether this risk is constant over time. Methods: The study was based on 3,139 participants of the Rotterdam Study, a population-based cohort study. All subjects were free from dementia, did not have a history of diabetes, and had fasting levels of glucose and insulin measured at baseline. Insulin resistance was estimated with the homeostasis model assessment. We investigated how fasting glucose, insulin, and insulin resistance are related to the risk of AD in 3 different strata according to time-to-event, using Cox proportional hazards models. Results: During follow-up, 211 participants developed AD, 71 of them within 3 years of baseline. Levels of insulin and insulin resistance were associated with a higher risk of AD within 3 years of baseline. After 3 years, the risk was no longer increased. Glucose was not associated with a higher risk of AD. There was no interaction of APOE ε4 carriership and insulin metabolism on the risk of AD. ConclusionS: Our findings suggest that insulin metabolism influences the clinical manifestation of AD only within 3 years. Copyrigh

Retinopathy and risk of dementia: the Rotterdam Study.

To investigate the relation between retinopathy and the risk of dementia. We investigated the associations between retinopathy and dementia and its subtypes Alzheimer disease (AD) and vascular dementia both cross-sectionally and prospectively in the Rotterdam Study, a large population-based cohort study. Digitized retinal images were available for 195 participants with prevalent dementia and 6,078 participants without dementia at baseline (1990-1993). Participants were reexamined in 1993-1994, 1997-1999, and 2002-2004 and were continuously monitored for development of dementia until January 1, 2007. Retinopathy was graded on fundus photographs and was defined as the presence of one or more dot/blot hemorrhages, microaneurysms, cotton wool spots, or evidence of laser treatment for retinopathy. Retinopathy was associated with prevalent dementia (age and sex-adjusted odds ratio 2.04, 95% confidence interval [CI] 1.34-3.09). Results were similar for AD and vascular dementia. During a mean follow-up of 11.4 years, 735 participants developed incident dementia, of whom 583 had AD and 80 had vascular dementia. There was no association of retinopathy at baseline with the risk of incident dementia during follow-up (age- and sex-adjusted hazard ratio 1.15, 95% CI 0.88-1.48) or the risk of incident AD or vascular dementia. Retinopathy is more prevalent in persons with dementia but is not associated with an increased risk of dementia over time. AD: Alzheimer disease ARIC: Atherosclerosis Risk in Communities CI: confidence interval CRP: C-reactive protein DSM-III-TR: Diagnostic and Statistical Manual of Mental Disorders, 3rd edition, revised GMS: Geriatric Mental State schedule MMSE: Mini-Mental State Examination OR: odds ratio

Plasma amyloid β, depression, and dementia in community-dwelling elderly

Plasma amyloid β (Aβ) levels have been associated with an increased risk of Alzheimer's disease (AD). As depression is common before the onset of AD, a few clinical studies tested the cross-sectional association of Aβ levels with depression in elderly and showed incongruous findings. Hence, we tested the longitudinal association between Aβ levels and depressive symptoms in community-dwelling elderly. The study is embedded in a population-based cohort of 980 participants aged 60 years or older from the Rotterdam Study with Aβ levels. Participants were evaluated for depressive symptoms with the Centre for Epidemiological Studies-Depression scale at baseline and repeatedly over the mean follow-up of 11 years. We first performed cross-sectional analyses. Then, we tested the longitudinal association between Aβ levels and depressive symptoms after excluding participants with dementia during follow-up. In cross-sectional analyses, persons with high Aβ1-40 levels had more clinically relevant depressive symptoms. However, this association was accounted for by persons with clinically relevant depressive symptoms who developed dementia within the next 11 years. In longitudinal analyses, persons with low levels of Aβ1-40 and Aβ1-42 without dementia had a higher risk of clinically relevant depressive symptoms during the follow-up. These findings suggest that the cross-sectional association between high plasma Aβ levels and clinically relevant depressive symptoms in the elderly is due to prodromal dementia. In contrast, the longitudinal association between low plasma Aβ levels and depressive symptoms could not be explained by dementia during follow-up suggesting that Aβ peptides may play a distinct role on depression etiology

Genome-wide analysis of genetic loci associated with Alzheimer disease

Context: Genome-wide association studies (GWAS) have recently identified CLU, PICALM, and CR1 as novel genes for late-onset Alzheimer disease (AD). Objectives: To identify and strengthen additional loci associated with AD and confirm these in an independent sample and to examine the contribution of recently identified genes to AD risk prediction in a 3-stage analysis of new and previously published GWAS on more than 35 000 persons (8371 AD cases). Design, Setting, and Participants: In stage 1, we identified strong genetic associations (P<10-3) in a sample of 3006 AD cases and 14 642 controls by combining new data from the population-based Cohorts for Heart and Aging Research in Genomic Epidemiology consortium (1367 AD cases [973 incident]) with previously reported results from the Translational Genomics Research Institute and the Mayo AD GWAS. We identified 2708 single-nucleotide polymorphisms (SNPs) with P<10-3. In stage 2, we pooled results for these SNPs with the European AD Initiative (2032 cases and 5328 controls) to identify 38 SNPs (10 loci) with P<10-5. In stage 3, we combined data for these 10 loci with data from the Genetic and Environmental Risk in AD consortium (3333 cases and 6995 controls) to identify 4 SNPs with P<1.7 × 10-8. These 4 SNPs were replicated in an independent Spanish sample (1140 AD cases and 1209 controls). Genome-wide association analyses were completed in 2007-2008 and the meta-analyses and replication in 2009. Main Outcome Measure: Presence of Alzheimer disease. Results: Two loci were identified to have genome-wide significance for the first time: rs744373 near BIN1 (odds ratio [OR],1.13; 95% confidence interval [CI],1.06-1.21 per copy of the minor allele; P=1.59×10-11) and rs597668 near EXOC3L2/BLOC1S3/ MARK4 (OR, 1.18; 95% CI, 1.07-1.29; P=6.45×10-9). Associations of these 2 loci plus the previously identified loci CLU and PICALM with AD were confirmed in the Spanish sample (P<.05). However, although CLU and PICALM were confirmed to be associated with AD in this independent sample, they did not improve the ability of a model that included age, sex, and APOE to predict incident AD (improvement in area under the receiver operating characteristic curve from 0.847 to 0.849 in the Rotterdam Study and 0.702 to 0.705 in the Cardiovascular Health Study). Conclusions: Two genetic loci for AD were found for the first time to reach genome-wide statistical significance. These findings were replicated in an independent population. Two recently reported associations were also confirmed. These loci did not improve AD risk prediction. While not clinically useful, they may implicate biological pathways useful for future research