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      The development of a stochastic mathematical model of Alzheimer’s disease to help improve the design of clinical trials of potential treatments

      1 , * , 1 , 1 , 2 , 1 , for the Alzheimer's Disease Neuroimaging Initiative

      PLoS ONE

      Public Library of Science

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          Abstract

          Alzheimer’s disease (AD) is a neurodegenerative disorder characterised by a slow progressive deterioration of cognitive capacity. Drugs are urgently needed for the treatment of AD and unfortunately almost all clinical trials of AD drug candidates have failed or been discontinued to date. Mathematical, computational and statistical tools can be employed in the construction of clinical trial simulators to assist in the improvement of trial design and enhance the chances of success of potential new therapies. Based on the analysis of a set of clinical data provided by the Alzheimer's Disease Neuroimaging Initiative (ADNI) we developed a simple stochastic mathematical model to simulate the development and progression of Alzheimer’s in a longitudinal cohort study. We show how this modelling framework could be used to assess the effect and the chances of success of hypothetical treatments that are administered at different stages and delay disease development. We demonstrate that the detection of the true efficacy of an AD treatment can be very challenging, even if the treatment is highly effective. An important reason behind the inability to detect signals of efficacy in a clinical trial in this therapy area could be the high between- and within-individual variability in the measurement of diagnostic markers and endpoints, which consequently results in the misdiagnosis of an individual’s disease state.

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          Most cited references 71

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          The amyloid hypothesis of Alzheimer's disease: progress and problems on the road to therapeutics.

           D. Selkoe,  John Hardy (2002)
          It has been more than 10 years since it was first proposed that the neurodegeneration in Alzheimer's disease (AD) may be caused by deposition of amyloid beta-peptide (Abeta) in plaques in brain tissue. According to the amyloid hypothesis, accumulation of Abeta in the brain is the primary influence driving AD pathogenesis. The rest of the disease process, including formation of neurofibrillary tangles containing tau protein, is proposed to result from an imbalance between Abeta production and Abeta clearance.
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            Hypothetical model of dynamic biomarkers of the Alzheimer's pathological cascade.

            Currently available evidence strongly supports the position that the initiating event in Alzheimer's disease (AD) is related to abnormal processing of beta-amyloid (Abeta) peptide, ultimately leading to formation of Abeta plaques in the brain. This process occurs while individuals are still cognitively normal. Biomarkers of brain beta-amyloidosis are reductions in CSF Abeta(42) and increased amyloid PET tracer retention. After a lag period, which varies from patient to patient, neuronal dysfunction and neurodegeneration become the dominant pathological processes. Biomarkers of neuronal injury and neurodegeneration are increased CSF tau and structural MRI measures of cerebral atrophy. Neurodegeneration is accompanied by synaptic dysfunction, which is indicated by decreased fluorodeoxyglucose uptake on PET. We propose a model that relates disease stage to AD biomarkers in which Abeta biomarkers become abnormal first, before neurodegenerative biomarkers and cognitive symptoms, and neurodegenerative biomarkers become abnormal later, and correlate with clinical symptom severity. Copyright 2010 Elsevier Ltd. All rights reserved.
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              Clinical and biomarker changes in dominantly inherited Alzheimer's disease.

              The order and magnitude of pathologic processes in Alzheimer's disease are not well understood, partly because the disease develops over many years. Autosomal dominant Alzheimer's disease has a predictable age at onset and provides an opportunity to determine the sequence and magnitude of pathologic changes that culminate in symptomatic disease. In this prospective, longitudinal study, we analyzed data from 128 participants who underwent baseline clinical and cognitive assessments, brain imaging, and cerebrospinal fluid (CSF) and blood tests. We used the participant's age at baseline assessment and the parent's age at the onset of symptoms of Alzheimer's disease to calculate the estimated years from expected symptom onset (age of the participant minus parent's age at symptom onset). We conducted cross-sectional analyses of baseline data in relation to estimated years from expected symptom onset in order to determine the relative order and magnitude of pathophysiological changes. Concentrations of amyloid-beta (Aβ)(42) in the CSF appeared to decline 25 years before expected symptom onset. Aβ deposition, as measured by positron-emission tomography with the use of Pittsburgh compound B, was detected 15 years before expected symptom onset. Increased concentrations of tau protein in the CSF and an increase in brain atrophy were detected 15 years before expected symptom onset. Cerebral hypometabolism and impaired episodic memory were observed 10 years before expected symptom onset. Global cognitive impairment, as measured by the Mini-Mental State Examination and the Clinical Dementia Rating scale, was detected 5 years before expected symptom onset, and patients met diagnostic criteria for dementia at an average of 3 years after expected symptom onset. We found that autosomal dominant Alzheimer's disease was associated with a series of pathophysiological changes over decades in CSF biochemical markers of Alzheimer's disease, brain amyloid deposition, and brain metabolism as well as progressive cognitive impairment. Our results require confirmation with the use of longitudinal data and may not apply to patients with sporadic Alzheimer's disease. (Funded by the National Institute on Aging and others; DIAN ClinicalTrials.gov number, NCT00869817.).
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                Author and article information

                Contributors
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: InvestigationRole: MethodologyRole: ValidationRole: VisualizationRole: Writing – original draftRole: Writing – review & editing
                Role: Data curationRole: Formal analysisRole: Writing – review & editing
                Role: Funding acquisitionRole: Writing – review & editing
                Role: Funding acquisitionRole: Writing – review & editing
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                29 January 2018
                2018
                : 13
                : 1
                PONE-D-17-23365
                10.1371/journal.pone.0190615
                5788351
                29377891
                © 2018 Hadjichrysanthou et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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                Figures: 4, Tables: 1, Pages: 19
                Product
                Funding
                Funded by: Janssen Prevention Centre
                Award Recipient :
                This study was funded by Janssen Prevention Centre, http://www.janssen.com/janssen-prevention-center, funding received by RMA. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Medicine and Health Sciences
                Mental Health and Psychiatry
                Dementia
                Alzheimer's Disease
                Medicine and Health Sciences
                Neurology
                Dementia
                Alzheimer's Disease
                Medicine and Health Sciences
                Neurology
                Neurodegenerative Diseases
                Alzheimer's Disease
                Biology and Life Sciences
                Neuroscience
                Cognitive Science
                Cognitive Neuroscience
                Cognitive Neurology
                Cognitive Impairment
                Biology and Life Sciences
                Neuroscience
                Cognitive Neuroscience
                Cognitive Neurology
                Cognitive Impairment
                Medicine and Health Sciences
                Neurology
                Cognitive Neurology
                Cognitive Impairment
                Medicine and Health Sciences
                Clinical Medicine
                Clinical Trials
                Medicine and Health Sciences
                Pharmacology
                Drug Research and Development
                Clinical Trials
                Research and Analysis Methods
                Clinical Trials
                Physical Sciences
                Mathematics
                Probability Theory
                Markov Models
                Biology and Life Sciences
                Neuroscience
                Cognitive Science
                Cognition
                Memory
                Biology and Life Sciences
                Neuroscience
                Learning and Memory
                Memory
                Physical Sciences
                Mathematics
                Probability Theory
                Probability Distribution
                Research and Analysis Methods
                Imaging Techniques
                Neuroimaging
                Biology and Life Sciences
                Neuroscience
                Neuroimaging
                Medicine and health sciences
                Clinical medicine
                Clinical trials
                Phase I clinical investigation
                Medicine and health sciences
                Pharmacology
                Drug research and development
                Clinical trials
                Phase I clinical investigation
                Research and analysis methods
                Clinical trials
                Phase I clinical investigation
                Custom metadata
                The data underlying this study were secured from ADNI, a third-party organization, and are available from http://adni.loni.usc.edu/data-samples/access-data/ for researchers who meet the criteria for access to data. All data required to replicate this study are available in the paper and its Supporting Information files.

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