Developing a global strategy to prevent Alzheimer's disease: Leon Thal Symposium 2010

The fourth Leon Thal Symposium (LTS2010) was convened in Toulouse, France, on November 3, 2010. This symposium reviewed design parameters that are necessary to develop comprehensive national databases on healthy aging. Such datasets offer the potential to serve as the foundation for a systems-approach to solve the dual public health problems of: (1) early detection of people who are at elevated risk for Alzheimer's disease, and (2) the development of interventions to delay onset of, or prevent, late-life dementia. The symposium considered three interrelated components of a National Database for Longitudinal Studies on Healthy Aging as follows: (a) a registry of healthy aging adults; (b) refined computer-based assessments for data gathering, including assessments of behavioral/memory changes associated with aging that are appropriate for broad use in nonexpert settings; and (c) high performance computing/supercomputer-based approaches for health data modeling and mining.

Meta-analysis confirms CR1, CLU, and PICALM as alzheimer disease risk loci and reveals interactions with APOE genotypes

OBJECTIVES

To determine whether genotypes at CLU, PICALM, and CR1 confer risk for Alzheimer disease (AD) and whether risk for AD associated with these genes is influenced by apolipoprotein E (APOE) genotypes.

DESIGN

Association study of AD and CLU, PICALM, CR1, and APOE genotypes.

SETTING

Academic research institutions in the United States, Canada, and Israel.

PARTICIPANTS

Seven thousand seventy cases with AD, 3055 with autopsies, and 8169 elderly cognitively normal controls, 1092 with autopsies, from 12 different studies, including white, African American, Israeli-Arab, and Caribbean Hispanic individuals.

RESULTS

Unadjusted, CLU (odds ratio [OR], 0.91; 95% confidence interval [CI], 0.85-0.96 for single-nucleotide polymorphism [SNP] rs11136000), CR1 (OR, 1.14; 95% CI, 1.07-1.22; SNP rs3818361), and PICALM (OR, 0.89; 95% CI, 0.84-0.94, SNP rs3851179) were associated with AD in white individuals. None were significantly associated with AD in the other ethnic groups. APOE ε4 was significantly associated with AD (ORs, 1.80-9.05) in all but 1 small white cohort and in the Arab cohort. Adjusting for age, sex, and the presence of at least 1 APOE ε4 allele greatly reduced evidence for association with PICALM but not CR1 or CLU. Models with the main SNP effect, presence or absence of APOE ε4, and an interaction term showed significant interaction between presence or absence of APOE ε4 and PICALM.

CONCLUSIONS

We confirm in a completely independent data set that CR1, CLU, and PICALM are AD susceptibility loci in European ancestry populations. Genotypes at PICALM confer risk predominantly in APOE ε4-positive subjects. Thus, APOE and PICALM synergistically interact.

Neuropathology of nondemented aging: presumptive evidence for preclinical Alzheimer disease

OBJECTIVE

To determine the frequency and possible cognitive effect of histological Alzheimer's disease (AD) in autopsied older nondemented individuals.

DESIGN

Senile plaques (SPs) and neurofibrillary tangles (NFTs) were assessed quantitatively in 97 cases from 7 Alzheimer's Disease Centers (ADCs). Neuropathological diagnoses of AD (npAD) were also made with four sets of criteria. Adjusted linear mixed models tested differences between participants with and without npAD on the quantitative neuropathology measures and psychometric test scores prior to death. Spearman rank-order correlations between AD lesions and psychometric scores at last assessment were calculated for cases with pathology in particular regions.

SETTING

Washington University Alzheimer's Disease Research Center.

PARTICIPANTS

Ninety-seven nondemented participants who were age 60 years or older at death (mean=84 years).

RESULTS

About 40% of nondemented individuals met at least some level of criteria for npAD; when strict criteria were used, about 20% of cases had npAD. Substantial overlap of Braak neurofibrillary stages occurred between npAD and no-npAD cases. Although there was no measurable cognitive impairment prior to death for either the no-npAD or npAD groups, cognitive function in nondemented aging appears to be degraded by the presence of NFTs and SPs.

CONCLUSIONS

Neuropathological processes related to AD in persons without dementia appear to be associated with subtle cognitive dysfunction and may represent a preclinical stage of the illness. By age 80-85 years, many nondemented older adults have substantial AD pathology.

GAB2 alleles modify Alzheimer's risk in APOE epsilon4 carriers

The apolipoprotein E (APOE) epsilon4 allele is the best established genetic risk factor for late-onset Alzheimer's disease (LOAD). We conducted genome-wide surveys of 502,627 single-nucleotide polymorphisms (SNPs) to characterize and confirm other LOAD susceptibility genes. In epsilon4 carriers from neuropathologically verified discovery, neuropathologically verified replication, and clinically characterized replication cohorts of 1411 cases and controls, LOAD was associated with six SNPs from the GRB-associated binding protein 2 (GAB2) gene and a common haplotype encompassing the entire GAB2 gene. SNP rs2373115 (p = 9 x 10(-11)) was associated with an odds ratio of 4.06 (confidence interval 2.81-14.69), which interacts with APOE epsilon4 to further modify risk. GAB2 was overexpressed in pathologically vulnerable neurons; the Gab2 protein was detected in neurons, tangle-bearing neurons, and dystrophic neuritis; and interference with GAB2 gene expression increased tau phosphorylation. Our findings suggest that GAB2 modifies LOAD risk in APOE epsilon4 carriers and influences Alzheimer's neuropathology.

Predicting lewy body pathology in a community-based sample with clinical diagnosis of Alzheimer's disease

Accurate antemortem prediction of Lewy body pathology in patients with dementia is problematic. This study generates a model that better predicts Lewy body pathology in community-based patients with clinical Alzheimer's disease. Lewy body pathology was detected in 80 of 152 participants (52.6%) with an initial diagnosis of probable Alzheimer's disease. In a stepwise logistic regression model, female gender, lower education, being married, bradykinesia, hallucinations, and absence of irritability predicted the greatest likelihood of Lewy body pathology. The predictive model correctly diagnosed Lewy body pathology with an estimated sensitivity of 75%, specificity of 68%, and accuracy of 72%; the area under the receiver operating characteristic curve was 0.75. In a community-based autopsy sample, this predictive model confirmed parkinsonism and hallucinations as important predictors of Lewy body pathology in patients with clinical Alzheimer's disease. The model also identified other demographic and clinical characteristics that might enhance the prediction of Lewy body pathology.

The North American Multiple System Atrophy Study Group

The North American Multiple System Atrophy Study Group involves investigators in 12 US medical centers funded by a grant from the National Institutes of Health. The objectives are to examine the environmental and genetic risk factors for MSA; elucidate pathogenic mechanisms underlying the disorder; and refine evaluations used for assessment. During its first year, the group enrolled 87 patients, implemented four cores, and initiated four scientific projects. Most patients among the 87 had parkinsonian features, which frequently began asymmetrically and remained asymmetrical; one-third responded to levodopa and many developed levodopa complications; almost two-thirds of the patients had cerebellar dysfunction, of these 90% had ataxia; urinary incontinence occurred commonly, and sleep disorders affected most. The investigators studied the effects of oxidative and nitrative stress upon the formation of alpha-synuclein inclusions; generated transgenic models of alpha-synuclein accumulation that recapitulate several behavioral and neuropathological features of MSA; and compared the severity of the autonomic features of MSA, Parkinson's disease and dementia with Lewy bodies.

Exercise is associated with reduced risk for incident dementia among persons 65 years of age and older

BACKGROUND

Alzheimer disease and other dementing disorders are major sources of morbidity and mortality in aging societies. Proven strategies to delay onset or reduce risk for dementing disorders would be greatly beneficial.

OBJECTIVE

To determine whether regular exercise is associated with a reduced risk for dementia and Alzheimer disease.

DESIGN

Prospective cohort study.

SETTING

Group Health Cooperative, Seattle, Washington.

PARTICIPANTS

1740 persons older than age 65 years without cognitive impairment who scored above the 25th percentile on the Cognitive Ability Screening Instrument (CASI) in the Adult Changes in Thought study and who were followed biennially to identify incident dementia.

MEASUREMENTS

Baseline measurements, including exercise frequency, cognitive function, physical function, depression, health conditions, lifestyle characteristics, and other potential risk factors for dementia (for example, apolipoprotein E epsilon4); biennial assessment for dementia.

RESULTS

During a mean follow-up of 6.2 years (SD, 2.0), 158 participants developed dementia (107 developed Alzheimer disease). The incidence rate of dementia was 13.0 per 1000 person-years for participants who exercised 3 or more times per week compared with 19.7 per 1000 person-years for those who exercised fewer than 3 times per week. The age- and sex-adjusted hazard ratio of dementia was 0.62 (95% CI, 0.44 to 0.86; P = 0.004). The interaction between exercise and performance-based physical function was statistically significant (P = 0.013). The risk reduction associated with exercise was greater in those with lower performance levels. Similar results were observed in analyses restricted to participants with incident Alzheimer disease.

LIMITATIONS

Exercise was measured by self-reported frequency. The study population had a relatively high proportion of regular exercisers at baseline.

CONCLUSION

These results suggest that regular exercise is associated with a delay in onset of dementia and Alzheimer disease, further supporting its value for elderly persons.

Gene expression correlates of neurofibrillary tangles in Alzheimer's disease

Neurofibrillary tangles (NFT) constitute one of the cardinal histopathological features of Alzheimer's disease (AD). To explore in vivo molecular processes involved in the development of NFTs, we compared gene expression profiles of NFT-bearing entorhinal cortex neurons from 19 AD patients, adjacent non-NFT-bearing entorhinal cortex neurons from the same patients, and non-NFT-bearing entorhinal cortex neurons from 14 non-demented, histopathologically normal controls (ND). Of the differentially expressed genes, 225 showed progressively increased expression (AD NFT neurons > AD non-NFT neurons > ND non-NFT neurons) or progressively decreased expression (AD NFT neurons < AD non-NFT neurons < ND non-NFT neurons), raising the possibility that they may be related to the early stages of NFT formation. Immunohistochemical studies confirmed that many of the implicated proteins are dysregulated and preferentially localized to NFTs, including apolipoprotein J, interleukin-1 receptor-associated kinase 1, tissue inhibitor of metalloproteinase 3, and casein kinase 2, beta. Functional validation studies are underway to determine which candidate genes may be causally related to NFT neuropathology, thus providing therapeutic targets for the treatment of AD.

Atherosclerosis and AD: analysis of data from the US National Alzheimer's Coordinating Center

BACKGROUND

Epidemiologic studies have implicated cerebrovascular disease and its antecedents as risk factors for Alzheimer disease (AD). Cerebral atherosclerosis or strokes may increase the deposition of neuritic plaques or the formation of neurofibrillary tangles. Alternatively, they may simply hasten the age at onset of disease, or increase the severity of disease symptoms. This investigation examined the association between cerebrovascular disease and the pathologic manifestations of AD in an autopsy series.

METHODS

This was a cross-sectional study using data from the United States National Alzheimer's Coordinating Center database. The primary analysis included 1,054 individuals with clinical information and semiquantitative neuropathologic measurements: 921 had AD as the primary neuropathologic diagnosis and 133 were considered neuropathologically normal.

RESULTS

Overall, 9% of the individuals had clinical history of stroke during life, but 33% had evidence of cerebral infarcts at postmortem. There was no association between neuritic plaques or neurofibrillary tangles, the primary neuropathologic manifestations of AD, with either clinical history of stroke or the presence of cerebral infarcts at postmortem. The authors did find a higher frequency of neuritic plaques and neurofibrillary tangles with increased amyloid angiopathy. Neither plaques nor tangles were associated with small vessel cerebrovascular disease, arteriosclerosis. However, the presence of large-vessel cerebrovascular disease, or atherosclerosis, was strongly associated with an increased frequency of neuritic plaques.

CONCLUSIONS

Atherosclerotic cerebrovascular disease may have a role in the pathogenesis of Alzheimer disease, because of a strong association with frequent neuritic plaques.

Similarities and differences in attitudes toward long-term care between Japanese Americans and Caucasian Americans

The purpose of this study was to compare attitudes toward the use of long-term care between older Japanese Americans (n = 1,244) and older Caucasian Americans (n = 1,354). When presented with a hypothetical situation in which they have dementia, 39% of older Japanese Americans and 42% of older Caucasians intended to be cared for at home, whereas 53% versus 38%, respectively, intended to use nursing home care (P <.001). If the hypothetical situation was hip fracture, 81% of older Japanese Americans and 72% of older Caucasians intended to be cared for at home, with 13% of both groups intending to use nursing home care (P = NS). The subjects' perceptions of what their families, friends, ministers, and communities would want them to choose differed, with more uncertainty among Caucasians (P <.001). For provision of home care, Japanese Americans were more likely to rely on loved ones than Caucasians, who were more likely to rely on paid providers. Multivariate logistic regression showed ethnicity to be independently related to intention to use nursing home care in the dementia scenario, controlling for demographic variables. Being married lowered the odds of intending to use nursing homes in any situation. We conclude that Caucasian Americans intend to use paid home health care at higher rates than Japanese Americans if they become disabled by dementia. Japanese Americans demonstrated more certainty about the influences of others on their opinions, suggesting a more stable cultural norm in this population, and intended to use more nursing home care in the event of permanent debility (dementia).

The utility of apolipoprotein E genotyping in the diagnosis of Alzheimer disease in a community-based case series

CONTEXT

A recent collaborative study found that apolipoprotein E (APOE) genotype, in conjunction with the clinical diagnosis of Alzheimer disease (AD), was useful in improving diagnostic specificity (correctly not diagnosing AD) relative to the clinical diagnosis alone. Since these samples are particularly enriched with patients with AD and the APOE epsilon4 allele, results may not be generalizable to patients seen in the general medical community.

OBJECTIVE

To evaluate the diagnostic utility of the APOE genotype in diagnosing AD in a community-based case series from the largest health maintenance organization in an urban area.

DESIGN

We examined the effect of including APOE genotype on the diagnosis of AD in a community-based case series of patients presenting with memory complaints.

PATIENTS

Clinical and neuropathologic diagnoses and APOE genotype were obtained from 132 patients who underwent evaluation for dementia and subsequent autopsy.

MAIN OUTCOME MEASURES

Sensitivity, specificity, and positive and negative predictive values given various combinations of clinical diagnoses and the presence of an APOE epsilon4 allele.

RESULTS

Of the 132 patients, 94 had neuropathologically confirmed AD, yielding a prevalence of 71%. The clinical diagnosis alone yielded a sensitivity of 84%, an estimated specificity of 50%, and positive and negative predictive values of 81% and 56%, respectively. The presence of an epsilon4 allele alone was associated with an estimated sensitivity of 59%, specificity of 71%, and positive and negative predictive values of 83% and 41%, respectively. Using the presence of clinical AD and an epsilon4 allele decreased the sensitivity to 49% and increased the specificity to 84%. The positive and negative predictive values were 88% and 40%, respectively. Alternatively, the clinical diagnosis of AD or the presence of an epsilon4 allele in individuals not meeting clinical criteria for AD increases the estimated sensitivity to 94% but decreases the specificity to 37%. The positive and negative predictive values were 79% and 70%, respectively. The changes in the sensitivity and specificity for the combined tests relative to clinical diagnosis alone offset each other. For lower prevalence communities, the positive predictive value will be much lower than those observed herein.

CONCLUSIONS

Our findings do not support the use of APOE genotyping alone in the diagnosis of AD in the general medical community. Although the presence of an epsilon4 allele in older persons with clinical AD increased the probability of having AD and the absence of an epsilon4 allele in this group decreased the probability of having AD, the association is not strong enough in the differential diagnosis of non-Alzheimer dementia and AD.

Clinico-neuropathological correlation of Alzheimer's disease in a community-based case series

OBJECTIVES

Most clinico-neuropathological correlative studies of Alzheimer's Disease (AD) are based on research cohorts that are not necessarily generalizable to patients seen in the general medical community. In this study, we examine the accuracy of the criteria used in diagnosing AD in a community-based case series of patients with memory complaints.

DESIGN AND PARTICIPANTS

Clinical and neuropathological diagnoses were obtained from 134 patients evaluated for dementia who subsequently underwent autopsy.

SETTING

Subjects who exhibited new symptoms of dementia and were enrolled in the University of Washington/Group Health Cooperative Alzheimer's Disease Patient Registry were eligible for this study.

MEASUREMENTS

Clinico-pathological correlation was performed using NINCDS-ADRDA (National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association) and CERAD (Consortium to Establish a Registry for Alzheimer's Disease) criteria.

RESULTS

Ninety-five of the 134 cases studied met CERAD neuropathological criteria for AD. The sensitivity of NINCDS-ADRDA "probable AD" was 83% (diagnosing AD correctly) and overall clinical diagnostic accuracy was 75%. However, there was a high rate of additional neuropathological findings. Only 34 of the 94 cases had pure AD on neuropathology, whereas the remainder frequently had coexisting vascular or Parkinson's disease lesions.

CONCLUSIONS

This study of a large series of community-based incident dementia cases provides a way of judging the adequacy of currently available clinical diagnostic criteria. It also shows that co-existing neuropathological findings are common in community-based AD.

Progression to dementia in patients with isolated memory loss

BACKGROUND

The diagnosis of dementia requires both memory loss and at least one other type of cognitive impairment. The natural history of patients with severe memory loss but no other type of cognitive impairment is poorly understood. We studied progression to dementia in patients with isolated memory loss.

METHODS

From a registry of 811 patients with cognitive complaints, 21 patients with severe isolated memory loss of unknown cause were identified and followed up for a mean of 48 months. A comparison group of 198 patients on the same register was identified with newly recognised cognitive complaints but without dementia or isolated memory loss (mean follow-up 31 months). We did a range of neuropsychological tests at intake.

FINDINGS

During follow-up, 48% (n = 10) of patients with isolated memory loss-developed dementia compared with 18% (n = 36) of the comparison group. Life-table analysis showed the mean times to a diagnosis of dementia was 3.77 years (95% CI 2.99-4.56) and 5.96 years (5.60-6.31), respectively (p = 0.01). The neuropsychological tests did not predict which patients would progress to dementia.

INTERPRETATION

Patients with severe isolated memory loss have an increased risk of developing dementia and should be closely followed-up.

Secreted amyloid beta-protein similar to that in the senile plaques of Alzheimer's disease is increased in vivo by the presenilin 1 and 2 and APP mutations linked to familial Alzheimer's disease

To determine whether the presenilin 1 (PS1), presenilin 2 (PS2) and amyloid beta-protein precursor (APP) mutations linked to familial Alzheimer's disease (FAD) increase the extracellular concentration of amyloid beta-protein (A beta) ending at A beta 42(43) in vivo, we performed a blinded comparison of plasma A beta levels in carriers of these mutations and controls. A beta 1-42(43) was elevated in plasma from subjects with FAD-linked PS1 (P < 0.0001), PS2N1411 (P = 0.009), APPK670N,M671L (P < 0.0001), and APPV7171 (one subject) mutations. A beta ending at A beta 42(43) was also significantly elevated in fibroblast media from subjects with PS1 (P < 0.0001) or PS2 (P = 0.03) mutations. These findings indicate that the FAD-linked mutations may all cause Alzhelmer's disease by increasing the extracellular concentration of A beta 42(43), thereby fostering cerebral deposition of this highly amyloidogenic peptide.

Impact of sample selection on APOE epsilon 4 allele frequency: a comparison of two Alzheimer's disease samples

OBJECTIVE

In a highly selected sample of unrelated Alzheimer's disease (AD) patients, we found that the APOE epsilon 4 allele frequency was higher than previously reported. Differing selection and ascertainment criteria may lead to these differences. To address this possibility, we compared the epsilon 4 allele frequency in two samples of AD patients selected from the same geographical area.

SETTING AND PARTICIPANTS

Cases (n = 55) and controls (n = 99) from a research clinic-based sample were compared with subjects (n = 537) from a community-based AD patient sample. The samples consisted of unrelated cases who met NINCDS/ADRDA criteria for probable AD.

DESIGN AND MEASUREMENTS

Clinical characteristics and APOE genotype data were obtained from AD cases and controls from both samples.

RESULTS

Frequency of APOE epsilon 4 allele in the research cases compared with the community cases (0.45 vs 0.36) was nearly significant. We compared demographic and clinical characteristics that might account for this difference and found that the research cases were younger, had an earlier age of onset, and had more advanced disease than the community cases. After onset age was controlled, there was no overall difference between epsilon 4 allele frequency of the two samples.

CONCLUSIONS

We found that the epsilon 4 allele frequency tended to be higher in the research AD sample compared the community-based sample. The two samples differed in several demographic and clinical characteristics. We conclude that research-based samples may lead to enrollment of younger patients with more severe disease who have higher APOE epsilon 4 allele load. This potential selection bias must be considered in the interpretation of studies of APOE allele frequency.

Geographically overlapping Alzheimer's disease registries: comparisons and implications

In the medical and epidemiologic literature, a registry denotes a data base in which registrants share some common characteristic such as disease category. One criticism of registries is that they frequently collect subjects in a haphazard fashion and, hence, are "nonrepresentative of the population purportedly being represented." In this report, we compare two registries: an incident-based Alzheimer's Disease Patient Registry (ADPR) recruiting subjects for epidemiologic studies from a large health maintenance organization; and an Alzheimer's Disease Research Center (ADRC) registry recruiting subjects for phenomenologic, biologic, and pharmacologic studies. While these registries share personnel, overlap geographically, and use similar diagnostic procedures, they differ substantially in their missions and resulting recruitment strategies. We compared these registries with respect to demographic characteristics and cognitive features at subject entry. Subjects enrolled in the incident-based registry are older and report shorter time between symptom onset and recruitment. They are less demented and mirror the general population demographically more closely than do subjects in the other registry. The ADRC registry contains a much greater proportion of subjects with higher educational attainment.

The Consortium to Establish a Registry for Alzheimer's Disease (CERAD). Part VI. Family history assessment: a multicenter study of first-degree relatives of Alzheimer's disease probands and nondemented spouse controls

Although familial factors in Alzheimer's disease (AD) are well established, uniform family-history assessment in genetic and epidemiologic studies of AD is needed to reconcile the divergent estimates of the cumulative risk of this illness among relatives of AD probands. To answer the need, the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) has developed a standardized Family History Assessment of AD to identify the presence of AD, Parkinson's disease (PD), and Down's syndrome (DS) in family members. This paper describes the use of this new assessment instrument in 118 patients with AD (estimated mean age at onset [+/- SD] = 64.5 +/- 7.7 years) and their nondemented spouses who were enrolled in 11 different CERAD sites in the U.S. The first-degree relatives of the probands with AD had a significantly greater cumulative risk (p < 0.005) of AD or primary progressive dementia (24.8%) than did the relatives of spouse controls (15.2%). Furthermore, the cumulative risk for this disorder among female relatives of probands was significantly greater than that among male relatives. There were no differences between the families of probands and controls for the numbers of affected first-degree relatives with PD or DS. This is the first reported multicenter family-history study of AD, and it supports earlier reports of familial factors in AD and indicates a higher risk to female relatives of AD probands. The CERAD Family History Assessment instrument may be useful for further multicenter and epidemiologic studies designed to delineate familial factors associated with AD.