Clinical Onset Of Alzheimer's Disease Research Articles

Default mode network and medial temporal lobe functional connectivity changes with Alzheimer’s disease severity and cognitive impairment in individuals with Down syndrome

AbstractBackgroundBy age 40, virtually all people with Down syndrome (DS) have sufficient beta‐amyloid and tau pathologies present to meet the criteria for pathological Alzheimer's disease (AD). Determining the timing and location of neurobiological changes caused by AD is critically important for effective intervention within this high‐risk population and more broadly in the general population, but little is known about the brain changes associated with clinical onset of AD in DS. Previous studies in sporadic AD suggest that functional connectivity of the default mode network (DMN) and medial temporal lobe (MTL) is vulnerable to AD pathology‐related impairment.MethodSeventy‐five individuals with DS (mean age 49.9±6.6, 36% women) from a subset of the Alzheimer’s Biomarkers Consortium ‐ Down Syndrome study underwent MRI, including an MPRAGE scan and a resting state functional scan. Participants completed a battery of neuropsychological tests and were assigned a consensus diagnosis for the presence or absence of mild cognitive impairment (MCI‐DS) or AD dementia. Forty‐eight participants were classified as cognitively stable (CS) (mean age 48±6.1, 42% women), 16 participants had MCI‐DS (mean age 50.8±4.2, 19% women), and 11 participants had dementia (mean age 57.2±6.6, 36% women).ResultParticipants with dementia had lower functional connectivity between the posterior DMN and the MTL relative to the CS and MCI‐DS groups. MCI‐DS participants had greater functional connectivity within the MTL relative to the CS group. Functional connectivity differences in these networks tracked with memory performance as well.ConclusionChanges in DMN and MTL functional connectivity are related to the progression of clinical symptoms of AD‐DS and may reflect synaptic changes stemming from AD pathology.

Risk Factors for Alzheimer's Disease: Focus on Stress.

In vulnerable individuals, chronic and persistent stress is an established risk factor for disorders that are comorbid with Alzheimer’s disease (AD), such as hypertension, obesity and metabolic syndrome, and psychiatric disorders. There are no disease-modifying drugs in the treatment of AD, and all phase-3 clinical trials with anti-amyloid drugs (e.g., β- or γ-secretase inhibitors and monoclonal antibodies) did not meet the primary endpoints. There are many reasons for the lack of efficacy of anti-amyloid drugs in AD, the most likely being a late start of treatment, considering that pathophysiological mechanisms underlying synaptic dysfunction and neuronal death begin several decades before the clinical onset of AD. The identification of risk factors is, therefore, an essential step for early treatment of AD with candidate disease-modifying drugs. Preclinical studies suggest that stress, and the resulting activation of the hypothalamic–pituitary–adrenal axis, can induce biochemical abnormalities reminiscent to those found in autoptic brain samples from individuals affected by AD (e.g., increases amyloid precursor protein and tau hyperphosphorylation). In this review, we will critically analyze the current knowledge supporting stress as a potential risk factor for AD.

Imaging tau and amyloid-β proteinopathies in Alzheimer disease and other conditions.

Most neurodegenerative disorders are associated with aggregated protein deposits. In the case of Alzheimer disease (AD), extracellular amyloid-β (Aβ) aggregates and intracellular tau neurofibrillary tangles are the two neuropathological hallmarks of the disease. Aβ-PET imaging has already been approved for clinical use and is being used in clinical trials of anti-Aβ therapies both for patient recruitment and as an outcome measure. These studies have shown that Aβ accumulation is a protracted process that can extend for more than 2 decades before the onset of clinical AD. This Review describes how in vivo brain imaging of Aβ pathology has revolutionized the evaluation of patients with clinical AD by providing robust and reproducible statements of global or regional brain Aβ burden and enabling the monitoring of disease progression. The role of selective tau imaging is discussed, focusing on how longitudinal tau and Aβ imaging studies might reveal the various effects (sequential and/or parallel, independent and/or synergistic) of these proteins on progression, cognition and other disease-specific biomarkers of neurodegeneration. Finally, imaging studies are discussed in the context of elucidating the respective roles of Aβ and tau in AD and in advancing our understanding of the relationship and/or interplay between these two proteinopathies.

Association Between Amyloid and Tau Accumulation in Young Adults With Autosomal Dominant Alzheimer Disease

It is critically important to improve our ability to diagnose and track Alzheimer disease (AD) as early as possible. Individuals with autosomal dominant forms of AD can provide clues as to which and when biological changes are reliably present prior to the onset of clinical symptoms. To characterize the associations between amyloid and tau deposits in the brains of cognitively unimpaired and impaired carriers of presenilin 1 (PSEN1) E280A mutation. In this cross-sectional imaging study, we leveraged data from a homogeneous autosomal dominant AD kindred, which allowed us to examine measurable tau deposition as a function of individuals' proximity to the expected onset of dementia. Cross-sectional measures of carbon 11-labeled Pittsburgh Compound B positron emission tomography (PET) and flortaucipir F 18 (previously known as AV 1451, T807) PET imaging were assessed in 24 PSEN1 E280A kindred members (age range, 28-55 years), including 12 carriers, 9 of whom were cognitively unimpaired and 3 of whom had mild cognitive impairment, and 12 cognitively unimpaired noncarriers. We compared carbon 11-labeled Pittsburgh Compound B PET cerebral with cerebellar distribution volume ratios as well as flortaucipir F 18 PET cerebral with cerebellar standardized uptake value ratios in mutation carriers and noncarriers. Spearman correlations characterized the associations between age and mean cortical Pittsburgh Compound B distribution volume ratio levels or regional flortaucipir standardized uptake value ratio levels in both groups. Of the 24 individuals, the mean (SD) age was 38.0 (7.4) years, or approximately 6 years younger than the expected onset of clinical symptoms in carriers. Compared with noncarriers, cognitively unimpaired mutation carriers had elevated mean cortical Pittsburgh Compound B distribution volume ratio levels in their late 20s, and 7 of 9 carriers older than 30 years reached the threshold for amyloidosis (distribution volume ratio level > 1.2). Elevated levels of tau deposition were seen within medial temporal lobe regions in amyloid-positive mutation carriers 6 years before clinical onset of AD in this kindred. Substantial tau deposition in the neocortex was only observed in 1 unimpaired carrier and in those with mild cognitive impairment. β-Amyloid uptake levels were diffusely elevated in unimpaired carriers approximately 15 years prior to expected onset of mild cognitive impairment. In carriers, higher levels of tau deposition were associated with worse performance on the Mini-Mental State Examination (entorhinal cortex: r = -0.60; P = .04; inferior temporal lobe: r = -0.54; P = .06) and the Consortium to Establish a Registry for Alzheimer Disease Word List Delayed Recall (entorhinal cortex: r = -0.86; P < .001; inferior temporal lobe: r = -0.70; P = .01). The present findings add to the growing evidence that molecular markers can characterize biological changes associated with AD in individuals who are still cognitively unimpaired. The findings also suggest that tau PET imaging may be useful as a biomarker to distinguish individuals at high risk to develop the clinical symptoms of AD and to track disease progression.

Loss of precuneus dendritic spines immunopositive for spinophilin is related to cognitive impairment in early Alzheimer's disease

Precuneus (PreC) cortex is affected with amyloid plaques early in Alzheimer's disease (AD), and this pathology may be associated with alterations in PreC synapses and cognitive impairment. We quantified the spinophilin-immunoreactive (ir) dendritic spine density and the intensity of spinophilin immunofluorescence, the latter as a measure of relative protein levels of spinophilin, in PreC lamina III from 33 subjects with clinical diagnoses of no cognitive impairment (NCI), mild cognitive impairment (MCI), mild-moderate AD (mAD), or severe AD (sAD). Both measures of spinophilin were lower in mAD and sAD compared with NCI. The MCI group had higher protein levels of spinophilin compared with mAD and sAD, and higher spinophilin-ir dendritic spine density compared with sAD. Lower spinophilin-ir dendritic spine density and relative protein levels of spinophilin were associated with greater amyloid beta (Aβ) plaque burden, detected with a derivative of Pittsburgh compound-B (6-CN-PiB), and worse cognitive performance. Clinical onset of AD is marked by the loss of PreC spinophilin-ir dendritic spines that is related to Aβ pathology and may contribute to cognitive symptoms early in the disease.

CAP--advancing the evaluation of preclinical Alzheimer disease treatments.

If we are to find treatments to postpone, reduce the risk of, or completely prevent the clinical onset of Alzheimer disease (AD), we need faster methods to evaluate promising preclinical AD treatments, new ways to work together in support of common goals, and a determination to expedite the initiation and performance of preclinical AD trials. In this article, we note some of the current challenges, opportunities and emerging strategies in preclinical AD treatment. We describe the Collaboration for Alzheimer's Prevention (CAP)-a convening, harmonizing and consensus-building initiative to help stakeholders advance AD prevention research with rigour, care and maximal impact-and we demonstrate the impact of CAP on the goals and design of new preclinical AD trials.

Higher education affects accelerated cortical thinning in Alzheimer's disease: a 5-year preliminary longitudinal study.

Epidemiological studies have reported that higher education (HE) is associated with a reduced risk of incident Alzheimer's disease (AD). However, after the clinical onset of AD, patients with HE levels show more rapid cognitive decline than patients with lower education (LE) levels. Although education level and cognition have been linked, there have been few longitudinal studies investigating the relationship between education level and cortical decline in patients with AD. The aim of this study was to compare the topography of cortical atrophy longitudinally between AD patients with HE (HE-AD) and AD patients with LE (LE-AD). We prospectively recruited 36 patients with early-stage AD and 14 normal controls. The patients were classified into two groups according to educational level, 23 HE-AD (>9 years) and 13 LE-AD (≤9 years). As AD progressed over the 5-year longitudinal follow-ups, the HE-AD showed a significant group-by-time interaction in the right dorsolateral frontal and precuneus, and the left parahippocampal regions compared to the LE-AD. Our study reveals that the preliminary longitudinal effect of HE accelerates cortical atrophy in AD patients over time, which underlines the importance of education level for predicting prognosis.

GABAergic neurotransmission and new strategies of neuromodulation to compensate synaptic dysfunction in early stages of Alzheimer's disease.

Alzheimer’s disease (AD) is a progressive neurodegenerative disease characterized by cognitive decline, brain atrophy due to neuronal and synapse loss, and formation of two pathological lesions: extracellular amyloid plaques, composed largely of amyloid-beta peptide (Aβ), and neurofibrillary tangles formed by intracellular aggregates of hyperphosphorylated tau protein. Lesions mainly accumulate in brain regions that modulate cognitive functions such as the hippocampus, septum or amygdala. These brain structures have dense reciprocal glutamatergic, cholinergic, and GABAergic connections and their relationships directly affect learning and memory processes, so they have been proposed as highly susceptible regions to suffer damage by Aβ during AD course. Last findings support the emerging concept that soluble Aβ peptides, inducing an initial stage of synaptic dysfunction which probably starts 20–30 years before the clinical onset of AD, can perturb the excitatory–inhibitory balance of neural circuitries. In turn, neurotransmission imbalance will result in altered network activity that might be responsible of cognitive deficits in AD. Therefore, Aβ interactions on neurotransmission systems in memory-related brain regions such as amygdaloid complex, medial septum or hippocampus are critical in cognitive functions and appear as a pivotal target for drug design to improve learning and dysfunctions that manifest with age. Since treatments based on glutamatergic and cholinergic pharmacology in AD have shown limited success, therapies combining modulators of different neurotransmission systems including recent findings regarding the GABAergic system, emerge as a more useful tool for the treatment, and overall prevention, of this dementia. In this review, focused on inhibitory systems, we will analyze pharmacological strategies to compensate neurotransmission imbalance that might be considered as potential therapeutic interventions in AD.

Routine lumbar puncture for the early diagnosis of Alzheimer's disease. Is it safe?

Routine lumbar puncture for the early diagnosis of Alzheimer's disease. Is it safe?

Change in Body Mass Index Before and After Alzheimer’s Disease Onset

A high body mass index (BMI) in middle-age or a decrease in BMI at late-age has been considered a predictor for the development of Alzheimer's disease (AD). However, little is known about the BMI change close to or after AD onset. BMI of participants from three cohorts, the Washington Heights and Inwood Columbia Aging Project (WHICAP; population-based) and the Predictors Study (clinic-based), and National Alzheimer's Coordinating Center (NACC; clinic-based) were analyzed longitudinally. We used generalized estimating equations to test whether there were significant changes of BMI over time, adjusting for age, sex, education, race, and research center. Stratification analyses were run to determine whether BMI changes depended on baseline BMI status. BMI declined over time up to AD clinical onset, with an annual decrease of 0.21 (p=0.02) in WHICAP and 0.18 (p=0.04) kg/m2 in NACC. After clinical onset of AD, there was no significant decrease of BMI. BMI even increased (b=0.11, p=0.004) among prevalent AD participants in NACC. During the prodromal period, BMI decreased over time in overweight (BMI≥25 and <30) WHICAP participants or obese (BMI≥30) NACC participants. After AD onset, BMI tended to increase in underweight/normal weight (BMI<25) patients and decrease in obese patients in all three cohorts, although the results were significant in NACC study only. Our study suggests that while BMI declines before the clinical AD onset, it levels off after clinical AD onset, and might even increase in prevalent AD. The pattern of BMI change may also depend on the initial BMI.

Polysomnographic and subjective sleep markers of mild cognitive impairment.

Growing evidence suggests that sleep disturbances precede by years the clinical onset of Alzheimer disease (AD). The goal of the current study is to determine whether changes in polysomnographic (PSG) sleep patterns accompany subjective sleep complaints in patients with mild cognitive impairment (MCI). We further examine whether meaningful changes in objective sleep physiology are predicted by self-reported sleep measures in MCI patients, and whether incipient neurodegeneration contributes to exacerbate sleep misperception. Overnight PSG recordings and self-reported sleep measures were obtained from 25 healthy elderly (HE) subjects and 25 patients with MCI at the sleep laboratory. Both PSG and self-reported sleep measures confirmed that sleep is altered in patients with MCI. Whereas subjective sleep responses predicted fragmentation of slow wave sleep (SWS) in HE individuals, this relationship was not evident in MCI patients. Furthermore, patients with MCI showed significant discrepancies in the estimation of sleep onset latency when compared with HE subjects. Sleep is significantly impaired in patients with mild cognitive impairment at both the objective and subjective level, which may be used as a surrogate marker of preclinical Alzheimer disease. Taken together, these findings aid in the development of novel therapeutic strategies devoted to improve sleep in the elderly population at risk of developing Alzheimer disease.

Cerebrospinal Fluid Aβ42, Phosphorylated Tau181, and Resting-State Functional Connectivity

Resting-state functional connectivity magnetic resonance imaging has great potential for characterizing pathophysiological changes during the preclinical phase of Alzheimer disease. To assess the relationship between default mode network integrity and cerebrospinal fluid biomarkers of Alzheimer disease pathology in cognitively normal older individuals. Cross-sectional cohort study at The Charles F. and Joanne Knight Alzheimer's Disease Research Center at Washington University in St Louis, St Louis, Missouri, among 207 older adults with normal cognition (Clinical Dementia Rating, 0). Resting-state functional connectivity magnetic resonance imaging measures of default mode network integrity. Decreased cerebrospinal fluid Aβ42 and increased cerebrospinal fluid phosphorylated tau181 were independently associated with reduced default mode network integrity, with the most prominent decreases in functional connectivity observed between the posterior cingulate and medial temporal regions. Observed reductions in functional connectivity were unattributable to age or structural atrophy in the posterior cingulate and medial temporal areas. Similar resting-state functional connectivity magnetic resonance imaging findings in relation to cerebrospinal fluid biomarkers were obtained using region-of-interest analyses and voxelwise correlation mapping. Both Aβ and tau pathology affect default mode network integrity before clinical onset of Alzheimer disease.

Body mass change in Alzheimer's disease

A high body mass index (BMI) at mid-age or a decrease in BMI at late-age has been considered as a predictor for the development of Alzheimer's disease (AD). However, little is known about the BMI change close to or after AD onset. BMI of participants from three cohorts -the Washington Heights / Inwood Columbia Aging Project (WHICAP; population-based), the Predictors Study (clinic-based), and the National Alzheimer's Coordinating Center (NACC; clinic-based)- were analyzed longitudinally. We separately examined change of BMI before AD diagnosis in incident AD patients and after AD diagnosis in incident and prevalent AD patients. We used generalized estimating equations to test whether there were significant changes of BMI over time, adjusting for age, sex, education, race, and research center (for NACC study and Predictors study). Stratification analyses were run to determine whether the BMI changes depended on baseline BMI status (underweight or normal <25 kg/m 2, overweight ≥25-<30 kg/m 2, and obese ≥30 kg/m 2). BMI declined over time up to AD clinical onset, with an annual decrease of 0.21 (p=0.02) and 0.19 (p=0.03) kg/m 2(in WHICAP and NACC, respectively). Following the clinical onset of AD, there was no longer a significant decrease of BMI. BMI even increased (b=0.10, p=0.01) in prevalent AD participants of NACC study. During the prodromal period BMI decreased significantly over time only in obese participants of the NACC study (β= -0.82, p<0.0001). During the period shortly after diagnosis of AD, BMI increased in underweight/normal weight subjects (β= 0.31, p<0.0001) and BMI decreased in obese subjects (β= -0.40, p=0.05) in NACC. Among prevalent AD participants, BMI increased in underweight/normal weight in Predictors study (β= 0.21, p=0.06) and NACC (β= 0.21, p<0.0001), and decreased in underweight/normal weight participants in NACC (β= -0.26, p=0.001). No significant change was observed for overweight subjects in any of the three cohorts. Our study suggests that while BMI declines before AD incidence, decline levels off after clinical AD onset and it might even increase. The pattern of BMI change may also depend on the initial BMI.

Ushering in the study and treatment of preclinical Alzheimer disease

Researchers have begun to characterize the subtle biological and cognitive processes that precede the clinical onset of Alzheimer disease (AD), and to set the stage for accelerated evaluation of experimental treatments to delay the onset, reduce the risk of, or completely prevent clinical decline. In this Review, we provide an overview of the experimental strategies, and brain imaging and cerebrospinal fluid biomarker measures that are used in early detection and tracking of AD, highlighting at-risk individuals who could be suitable for preclinical monitoring. We discuss how advances in the field have contributed to reconceptualization of AD as a sequence of biological changes that occur during progression from preclinical AD, to mild cognitive impairment and finally dementia, and we review recently proposed research criteria for preclinical AD. Advances in the study of preclinical AD have driven the recognition that efficacy of at least some AD therapies may depend on initiation of treatment before clinical manifestation of disease, leading to a new era of AD prevention research.

Epigenetic drugs for Alzheimer's disease: hopes and challenges

In his letter Peedicayil [1] suggests that epigenetic mechanisms, in particular histone deacetylases (HDACs) and gene methylation, might represent a promising target for drug discovery in Alzheimer's disease (AD). In our recent review [2] we focused on disease modifying drugs in advanced clinical development (Phase II/III). Therefore we did not discuss drugs that specifically exert epigenetic effects, because none of them so far has reached advanced clinical development for AD. However, as suggested by Peedicayil, epigenetic mechanisms in neurodegenerative diseases have been the object of intensive research in recent years and deserve attention because they might soon constitute a novel paradigm in AD arena. Histone acetylation is dynamically regulated by histone acetyltransferases (HATs) and HDACs. HATs neutralize the positive charge on lysine residues allowing chromatin to adopt a more relaxed structure and to recruit the transcriptional machinery. HDACs reverse lysine acetylation, restore histone positive charge and locally stabilize chromatin architecture [3]. Thus, the level of histone acetylation dramatically affects chromatin condensation and gene transcription. DNA methylation is also involved in histone modification. Methylation of CpG islands in promoter regions is associated with gene silencing and is highly interactive with histone acetylation and the other histone-modifying mechanisms [3]. Studies of late-onset AD in twins support the notion that risk factors may affect AD pathophysiology through epigenetic mechanisms [4]. On the other hand, some AD risk factors, such as chronic stress [5], induce strong epigenetic modifications in animal models [6]. Alteration of physiological stress responses, such as those affecting the hypothalamic-pituitary-adrenal axis, may further increase the epigenetic impact of chronic adverse stress in AD [7]. Chronic psychological distress has been also associated with late-life non-AD dementia [8], but the role of epigenetic mechanisms in this condition has not been investigated so far. HDAC2, but not HDAC1, is known as a negative regulator of memory [9]. Cognitive function in AD may be affected by an epigenetic blockade of gene transcription. A recent study suggests that this blockade is mediated by HDAC2 in patients with AD and shows that it is potentially reversible in mouse models of neurodegeneration [10]. Non-specific pan-HDAC inhibitors include valproic acid, trichostatin A, sodium 4-phenylbutyrate and vorinostat. All these drugs, however, have been shown to affect, by different mechanisms, Aβ plaque deposition and/or tau hyperphosphorylation [11]. It remains unclear, therefore, whether or not these drugs, endowed with neuroprotective action in vitro, re-instate memory and reverse learning deficits in AD mouse models through Aβ clearance, rather than primarily through HDAC inhibition. The causal involvement of epigenetic mechanisms in AD, if confirmed, may help in understanding failure of clinical trials with disease modifying drugs despite their proven efficacy in Aβ clearing. According to this view, if the epigenetic blockade starts before the clinical onset of AD, then reducing Aβ generation and deposition alone may not be sufficient to rescue cognitive functions. Finally, as with any novel drug treatment, epigenetic modifiers must be carefully considered in terms of safety and tolerability, particularly considering the fundamental role of epigenetics in the regulation of global gene expression patterns. HDAC inhibitors have been initially studied and used in neoplastic diseases, such as haematological malignancies [3]. Vorinostat and romidepsin were first approved for the treatment of cutaneous T cell lymphoma, but the potential therapeutic utility of HDAC inhibitors for non-oncology indications requires more stringent safety profiles. Key safety issues include the long term effects on stem cells and germ cells. Potential effects on human reproduction are not relevant in AD patients (generally beyond the reproductive age), but other effects involving immune function [12, 13] might prevent the use of HDAC inhibitors in AD patients. Furthermore it should be considered that HDAC inhibitors developed for cancer may poorly permeate the blood–brain barrier [14]. Recently a CNS-penetrant HDAC (Class I) inhibitor, EVP-0334, has been developed and studied in a phase I clinical trial for the treatment of AD [3], but further detailed information has not yet been disclosed. Identification of subtype- or target-selective HDAC inhibitors, such as for HDAC2 will hopefully provide, in the near future, transcriptional and synaptic effects in neurons, with fewer off target effects, making possible the clinical development of these drugs for AD.

The Microtubule-Associated Protein 1A (MAP1A) is an Early Molecular Target of Soluble Aβ-Peptide

A progressive accumulation of amyloid β-protein (Aβ) is widely recognized as a pathological hallmark of Alzheimer's disease (AD). Substantial progress has been made toward understanding the neurodegenerative cascade initiated by small soluble species of Aβ and recent evidence supports the notion that microtubule rearrangements may be proximate to neuritic degeneration and deficits in episodic declarative memory. Here, we examined primary cortical neurons for changes in markers associated with synaptic function following exposure to sublethal concentrations of non-aggregated Aβ-peptide. This data show that soluble Aβ species at a sublethal concentration induce degradation of the microtubule-associated protein 1A (MAP1A) without concurrently affecting dendritic marker MAP2 and/or the pre-synaptic marker synaptophysin. In addition, MAP1A was found to highly co-localize with the postsynaptic density-95 (PSD-95) protein, proposing that microtubule perturbations might be central for the Aβ-induced neuronal dysfunctions as PSD-95 plays a key role in synaptic plasticity. In conclusion, this study suggests that disruption of MAP1A could be a very early manifestation of Aβ-mediated synaptic dysfunction-one that presages the clinical onset of AD by years. Moreover, our data support the notion of microtubule-stabilizing agents as effective AD drugs.

Alzheimer’s disease: ageing-related or age-related? New hypotheses from an old debate

The view that Alzheimer's disease (AD) is a fatal outcome of ageing prevails over the view that it mainly affects people aged 75-95. The former is based on the exponential increase in the incidence of AD with ageing, while the latter on AD prevalence rates. Both views share the idea that neurofibrillary degeneration (NFD) is secondary to the loading of β-protein (Aβ) and its more toxic species in nervous tissue that occurs with ageing in everybody, but is greater in people predisposed to AD. They differ in terms of the complexity attributed to the concept of neuronal vulnerability to Aβ. In the ageing-related hypothesis, it is seen as a phylogenetic characteristic of neurons that predisposes some of them to Aβ-dependent NFD, which spreads from the more vulnerable allocortex to the less vulnerable neocortex and accordingly causes memory decline progressing to dementia. To adapt this to the discontinuity of AD prevalence, it is necessary to see neuronal vulnerability as being modulated by additional ontogenetic factors that make some vulnerable neurons more or less sensitive to Aβ toxicity. This may give the Aβ/NFD relationship enough flexibility to explain the cognitive reserve of the oldest old and the phenotypical variability of AD, in particular why it is that the clinical onset of AD may be characterised by focal signs other than memory loss. Introducing this concept offers a new perspective of AD pathogenesis based on the role played by Aβ and related proteins in nerve cell selection during brain development and adult neurogenesis.

Elevation of β-Amyloid 1-42 Autoantibodies in the Blood of Amnestic Patients With Mild Cognitive Impairment

To develop a blood-based test for screening populations at risk for Alzheimer disease. Case-control study. Subjects A total of 180 patients with mild cognitive impairment (MCI) and 105 age-matched, cognitively normal controls. The titer of beta-amyloid 1-42 autoantibodies in the plasma was obtained at the time of diagnosis and evaluated by enzyme-linked immunosorbent assay before and after dissociation of the antigen-antibody complexes. A total of 107 patients with MCI were followed up for 36 months; 70 of the 107 cases progressed to Alzheimer disease. The average level of beta-amyloid 1-42 plasma autoantibodies in patients with MCI that progressed to Alzheimer disease, but not that of the stable cases, was significantly higher than in cognitively normal controls (P < .001). The results suggest that the plasma beta-amyloid 1-42 autoantibodies parallel beta-amyloid 42 deposition in the brain, which is known to precede by several years the clinical onset of Alzheimer disease. The evaluation of beta-amyloid 1-42 autoantibodies after dissociation of the complexes is a simple and inexpensive method that can be used to predict the occurrence of Alzheimer disease.

Association of early-onset Alzheimer's disease with an interleukin-1? gene polymorphism

Overexpression of the pluripotent cytokine interleukin-1 (IL-1) by microglial cells correlates with formation of neuritic beta-amyloid plaques in Alzheimer's disease (AD). We evaluated polymorphisms in the genes coding for the IL-1alpha, IL-1beta, and IL-1 receptor antagonist cytokines, and tested their association with the occurrence and age at onset of sporadic AD. We found a strong association between the IL-1A T/T genotype and AD onset before 65 years of age (odds ratio, 4.86), with carriers of this genotype showing an onset of disease 9 years earlier than IL-1A C/C carriers. A weaker association with the age at onset was also shown for the IL-1B and IL-1RN genes. These data suggest either a direct effect of the IL-1 gene family, mainly IL-1A, on the clinical onset of AD, or a linkage dysequilibrium with an unknown locus relevant to AD on chromosome 2.