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Alzheimer's Disease (G30.9)

Alzheimer’s disease is the leading cause of dementia, accounting for roughly 60–70% of cases worldwide and affecting more than 55 million people globally, including approximately 6–7 million in the United States alone. Its prevalence rises exponentially with age—doubling about every five years after 65—and nearly one in three individuals over 85 is affected, with women disproportionately impacted due to longevity and potential sex-specific biological factors. Beyond its profound emotional and economic toll, Alzheimer’s is now understood not simply as a disorder of amyloid plaques and tau tangles, but as a systems-level neurodegenerative process involving impaired protein clearance, neuroinflammation, synaptic dysfunction, vascular contributions, and genetic risk modifiers such as APOE ε4. Precision medicine has reshaped the field through biomarker-driven diagnosis (CSF and plasma Aβ/tau ratios, PET imaging), genotype-informed risk stratification, and targeted pathway modulation aimed at amyloid processing, tau aggregation, and microglial signaling. These advances are enabling earlier intervention, biologically defined patient segmentation, and more rational clinical trial design—shifting the therapeutic paradigm from symptomatic management toward mechanism-based disease modification.

Causes

The etiology of Alzheimer’s disease is multifactorial, arising from the convergence of genetic susceptibility, age-related proteostatic failure, metabolic and vascular stress, and maladaptive neuroimmune responses. In rare early-onset familial forms, autosomal dominant mutations in APP, PSEN1, or PSEN2 alter amyloid precursor protein processing, increasing production of aggregation-prone Aβ42 peptides and accelerating plaque deposition. In late-onset disease—the vast majority of cases—risk is polygenic, with APOE ε4 influencing lipid transport, amyloid clearance, and microglial phenotype. Aging-related impairments in proteostasis, mitochondrial function, and glymphatic clearance promote accumulation of misfolded proteins, including hyperphosphorylated tau, which spreads trans-synaptically and disrupts cytoskeletal stability. Concurrently, chronic neuroinflammation driven by microglial and complement activation amplifies synaptic pruning and neuronal injury, while vascular dysfunction and metabolic disease exacerbate hypoperfusion and oxidative stress. Rather than a single initiating lesion, Alzheimer’s emerges from dynamic network-level dysregulation in which protein aggregation, inflammation, synaptic failure, and systemic risk factors interact over decades before clinical symptoms appear.

Pathophysiology

Alzheimer’s disease pathophysiology reflects a progressive breakdown of synaptic and neuronal network integrity driven by interacting molecular cascades. Aberrant cleavage of amyloid precursor protein generates aggregation-prone Aβ peptides that oligomerize and deposit extracellularly, disrupting synaptic signaling and calcium homeostasis. Intraneuronally, hyperphosphorylated tau detaches from microtubules, misfolds, and propagates trans-synaptically, impairing axonal transport and cytoskeletal stability. These proteinopathies activate microglia and astrocytes, initiating a chronic neuroinflammatory state characterized by cytokine release, complement activation, and maladaptive synaptic pruning. Concurrent mitochondrial dysfunction, oxidative stress, and impaired proteostasis further compromise neuronal survival, while cerebrovascular insufficiency reduces metabolic support and accelerates degeneration. The cumulative effect is network-level disconnection—particularly within hippocampal and cortical circuits—leading to progressive memory loss, executive dysfunction, and ultimately widespread cortical atrophy.

Clinical features

Alzheimer’s disease typically presents insidiously with episodic memory impairment, particularly difficulty forming and retaining new information, reflecting early involvement of the hippocampus and medial temporal lobe structures. Patients often exhibit repetitive questioning, misplacement of objects, and increasing reliance on reminders. As the disease progresses, deficits extend to executive function, language (anomia, word-finding difficulty), visuospatial processing, and impaired judgment, leading to functional decline in complex activities such as financial management or navigation. Behavioral and neuropsychiatric symptoms—including apathy, depression, irritability, sleep disturbance, and later agitation or psychosis—are common and often contribute substantially to caregiver burden. In advanced stages, patients develop profound cognitive impairment, loss of independence in basic activities of daily living, motor slowing, dysphagia, and eventual immobility. The clinical course is typically gradual over years, with progression reflecting the spread of underlying neurodegenerative pathology across cortical networks.

Diagnosis

The diagnosis of Alzheimer’s disease is based on a combination of clinical assessment, cognitive testing, functional evaluation, and biomarker evidence. Clinically, patients demonstrate a progressive decline in memory and other cognitive domains that interferes with daily functioning, confirmed through structured tools such as the MoCA or MMSE alongside detailed history from the patient and informants. Laboratory testing is performed to exclude reversible causes of cognitive impairment (e.g., thyroid dysfunction, B12 deficiency). Neuroimaging—typically MRI—assesses for medial temporal lobe atrophy and excludes alternative structural pathology. Increasingly, biomarker confirmation is incorporated into diagnostic frameworks: cerebrospinal fluid analysis showing reduced Aβ42 and elevated phosphorylated tau, plasma biomarker assays, or amyloid and tau PET imaging provide biological evidence of underlying pathology. Current diagnostic criteria emphasize a biologically defined continuum in which Alzheimer’s pathology may be identified years before overt dementia, enabling earlier and more precise stratification for therapeutic intervention.

Mechanism of action videos

Biological pathways

  • Tight junction
  • T cell receptor signaling pathway
  • Regulation of actin cytoskeleton
  • Ras signaling pathway
  • Protein processing in endoplasmic reticulum
  • Regulation of MITF-M-dependent genes involved in cell cycle and proliferation
  • Proteasome
  • Oxidative phosphorylation
  • NF-kappa B signaling pathway
  • Leukocyte transendothelial migration
  • Insulin signaling pathway
  • IgSF CAM signaling
  • Focal adhesion
  • Defective Base Excision Repair Associated with OGG1
  • Cell adhesion molecule (CAM) interaction
  • Calcium signaling pathway
  • Defective Intrinsic Pathway for Apoptosis
  • Autophagy - animal
  • Apoptosis
  • Alzheimer's disease and miRNA effects
  • Alzheimer disease
  • Adherens junction
  • AGE-RAGE signaling pathway in diabetic complications
  • Generic Transcription Pathway
  • Oncogene Induced Senescence
  • Assembly and cell surface presentation of NMDA receptors
  • RNA Polymerase II Transcription
  • Neurodegenerative Diseases
  • Deregulated CDK5 triggers multiple neurodegenerative pathways in Alzheimer's disease models
  • Gene expression (Transcription)
  • EPH-Ephrin signaling
  • Cellular Senescence
  • Synaptic adhesion-like molecules
  • Unblocking of NMDA receptors, glutamate binding and activation
  • Negative regulation of NMDA receptor-mediated neuronal transmission
  • NOTCH4 Activation and Transmission of Signal to the Nucleus
  • Long-term potentiation
  • Diseases of programmed cell death
  • Diseases of cellular response to stress
  • Diseases of Cellular Senescence

Clinical trials

  • The Pain Identification and Communication Toolkit: A Training Program to Support Family Caregivers of Persons With ADRD
  • Impact of a Novel Socially Assistive Robotic Architecture on Engaging Older Adults With Mild Cognitive Impairment, Alzheimer's Disease and Related Dementia in Long Term Care Settings
  • Attenuation of Postprandial Inflammatory Processes in Alzheimer's Disease Patients by Consumption of Pomace Oil
  • D- PRESCRIBE-AD Phase 2(The Developing a PRogram to Educate and Sensitize Caregivers to Reduce the Inappropriate Prescription Burden in Elderly With Alzheimer's Disease Study: Trial 2)
  • A Phase 3, Randomized, Double-Blind, Placebo-Controlled, Parallel Group Study to Evaluate the Safety and Efficacy of KarXT for the Treatment of Psychosis Associated With Alzheimer's Disease
  • Assessment of Foralumab Safety and Modulation of Microglial Activation Evaluated by PET Imaging in Patients With Early Symptomatic Alzheimer's Disease
  • Early Onset Alzheimer's Disease Genomic Study
  • Blood Biomarkers for Early and Accurate Diagnosis of Alzheimer's Disease in Primary Care
  • Neurophysiological Benefits of Live Music for Early Alzheimer's Patients and Their Caregivers
  • Automated, Assistive, Non-Contact Sleep Quality Monitor for Individuals With Alzheimer's Disease
  • Postherpetic Neuralgia After Herpes Zoster and Risk of Incident Dementia: Real-World Evidence From an International Matched Cohort With Landmark Analysis
  • A Phase 3, Randomized, Double-Blind, Placebo-Controlled, Parallel Group Study to Evaluate the Safety and Efficacy of KarXT + KarX-EC for the Treatment of Agitation Associated With Alzheimer's Disease
  • Task-evoked Pupillometry in AD, MCI, and Depression-Related Cognitive Impairment
  • Wearables-and Blood-based Biomarkers-incorporated Modernisation of Circadian Rhythm Disruption Management in People Living With Alzheimer's Dementia: A Stepwise Study From Digital Inclusivity, Digital Therapy, to Digital Phenotyping and Biomarker Exploration
  • Care for America's Aging (CfAA): A Study to Improve Behavioral and Quality of Life Outcomes of Older Adults With Cognitive Impairment and Dementia and Their Care Partners
  • A Phase 2, Placebo-Controlled, Double-Blind, Parallel-Group, Dose-Finding Study to Evaluate Safety, Tolerability, and Biomarker Efficacy of E2814 With Concurrent Lecanemab Treatment in Subjects With Early Alzheimer's Disease
  • Detection of Elevated Plasma pTau217 in Donated Human Blood Samples: Implications for Blood Transfusion Safety
  • Efficacy of Virtual Reality Reminiscence Therapy in Nursing Home Residents With Alzheimer's Disease or Related Diseases
  • Decision Making and Implementation of Aging-in-Place/Long Term Care Plans Among Older Adults
  • Development of a Database to Investigate Digital and Blood-Based Biomarkers and Their Relationship to Tau and Amyloid PET Imaging in Older Participants Who Are Cognitively Normal (CN), Have Mild Cognitive Impairment (MCI), or Have Mild-to-Moderate AD Dementia
  • A Phase 3, Randomized, Double-Blind, Placebo-Controlled, Parallel Group Study to Evaluate the Safety and Efficacy of KarXT + KarX-EC for the Treatment of Agitation Associated With Alzheimer's Disease
  • Unraveling the SIGNature of ALzheimer's Disease: Integrating Multimodal Biomarkers Through Machine Learning
  • Facilitating the Measurement and Treatment of the Behavioral Symptoms of Dementia (BPSD) and Understanding Caregiver Burden Using Wearable Devices in Rural Taiwan - A Dyadic Feasibility Pilot Study
  • Randomized, Double-Blind, Placebo-Controlled Investigation to Validate the Efficacy and Safety of an Auditory Stimulation Treatment During Sleep to Improve Cognitive Abilities Related to Long-Term Memory in Amnestic Mild Cognitive Impairment (aMCI)
  • Advancing Alzheimer's Care: Home-based tDCS (Transcranial Direct Current Stimulator) for Affective Symptoms
  • Sleep Interventions and Neurocognitive Outcomes in Amnestic Mild Cognitive Impairment
  • Supporting Our Caregivers In ADRD Learning (SOCIAL): Reducing Stress for Caregivers of Persons With Dementia, a Pilot Randomized Control Trial
  • A Multicenter, Randomized, Double-Blind, Placebo-Controlled Phase 2a Study to Evaluate the Effect of HT-4253 for the Prevention of Alzheimer's Disease in APOE4 Carriers
  • Global Study to Investigate Safety and Efficacy of Donanemab in Early Symptomatic Alzheimer's Disease
  • A Phase 3, Randomized, Double-Blind, Placebo-Controlled, Parallel-Group Study to Evaluate the Efficacy and Safety of KarXT + KarX-EC for the Treatment of Cognitive Impairment Associated With Mild to Moderate Alzheimer's Disease (MINDSET 1)
  • Impact of Novel Rehabilitative Approaches for Dysphagia in Patients With Alzheimer's Disease and Related Dementias
  • Improving Primary Care Clinician's Advance Care Planning Alzheimer's Disease and Related Dementias
  • A Longitudinal, Prospective Epidemiology Study in Alzheimer's Disease: Assessing Neurocognitive and Biomarker Changes and Health Outcomes in Individuals at Risk for Symptoms of Alzheimer's Disease (ANCHOR-AD)
  • A Phase 2 Randomized, Placebo-Controlled, Double-Blind, Parallel-group Study to Evaluate the Efficacy and Safety of MK-1167 as Adjunctive Therapy in Participants With Mild to Moderate Alzheimer's Disease Dementia
  • TRIAD - Tracking Risk in Integrated Alzheimer's Diagnostics. A Biopsychosocial Model for the Early and Accurate Diagnosis of the Alzheimer's Disease Continuum.
  • A Phase 3, Randomized, Double-Blind, Placebo-Controlled, Efficacy and Safety Study of Povorcitinib in Participants With Prurigo Nodularis
  • A Nutritional Intervention for Body, Brain, and Longevity Effects (NIBBLE) - A Randomized Open-label Intervention of the Fasting-mimicking Diet (FMD)
  • Master Screening Study to Determine Individuals With Potential Trial Eligibility for Alzheimer's Disease Studies as Assessed by Biomarker Status and Cognition
  • CommunityRx-Dementia + Peer Navigation (CRxDpeer): A Real-World Implementation and Effectiveness Study of an IT-Based Social Care Intervention
  • A Community-Based Approach for ALDH2 Genetic Testing in East Asian Americans

Therapeutic area: Neurology