8:54
Alzheimer's disease - plaques, tangles, causes, symptoms & pathology
Osmosis from Elsevier
Overview
This video explains Alzheimer's disease, the most common cause of dementia. It details the underlying pathology, focusing on the roles of beta-amyloid plaques and tau tangles in neurodegeneration. The video differentiates between sporadic (late-onset) and familial (early-onset) forms of the disease, discussing genetic risk factors like APOE-e4 and mutations in PSEN-1/PSEN-2, as well as the link to Down syndrome. Finally, it outlines the progressive symptoms, diagnostic challenges, and current lack of a cure.
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Chapters
- Dementia is a set of symptoms (like memory loss) that impair independent function, not a disease itself.
- Alzheimer's disease is the most common cause of dementia.
- Alzheimer's is a neurodegenerative disease, meaning it causes the loss of neurons, particularly in the brain's cortex.
Understanding Alzheimer's as a specific neurodegenerative disease helps clarify its biological basis and distinguish it from the broader category of dementia.
- Amyloid precursor protein (APP) is normally broken down by alpha and gamma secretase.
- When beta secretase and gamma secretase interact with APP, they produce sticky amyloid-beta monomers.
- These monomers clump together outside neurons, forming beta-amyloid plaques that disrupt neuron signaling and can trigger inflammation.
- Plaques can also deposit around brain blood vessels (amyloid angiopathy), weakening them and increasing hemorrhage risk.
Identifying plaques as a key pathological hallmark helps explain how neuronal communication is disrupted, leading to cognitive decline.
Histology images showing clumps of beta-amyloid outside brain cells.
- Neurons rely on microtubules, supported by tau protein, to transport nutrients.
- Beta-amyloid buildup may trigger internal processes that cause tau to detach from microtubules and clump together inside neurons, forming neurofibrillary tangles.
- This disrupts nutrient transport and can lead to neuron death (apoptosis).
Understanding tangles explains the internal cellular damage within neurons, complementing the external damage caused by plaques and contributing to neuron loss.
Histology images showing neurofibrillary tangles inside brain cells.
- As neurons die, the brain atrophies (shrinks), leading to narrower gyri, wider sulci, and enlarged ventricles.
- Alzheimer's is divided into sporadic (late-onset, common, likely due to genetics and environment) and familial (early-onset, rare, caused by specific inherited gene mutations).
- Age is a major risk factor for sporadic Alzheimer's.
- The APOE-e4 gene variant increases risk by being less effective at breaking down beta-amyloid.
Distinguishing between sporadic and familial Alzheimer's helps explain the varying onset ages and genetic predispositions, guiding research and potential interventions.
Increased risk of Alzheimer's with one or two copies of the APOE-e4 allele.
- Familial Alzheimer's is often early-onset and linked to mutations in genes like PSEN-1 and PSEN-2, which affect how gamma-secretase processes APP.
- These mutations can lead to the production of beta-amyloid fragments that more readily form plaques.
- Down syndrome (Trisomy 21) also increases Alzheimer's risk because the APP gene is on chromosome 21, leading to potentially higher APP levels and plaque formation.
Identifying specific gene mutations provides concrete biological targets for understanding disease mechanisms and developing future therapies.
Mutations in PSEN-1 or PSEN-2 genes altering gamma-secretase activity and leading to increased plaque formation.
- Symptoms progress from early memory loss to difficulties with motor skills, language, and eventually long-term memory and disorientation.
- Late-stage patients become bedridden, with infection often being the cause of death.
- Definitive diagnosis requires autopsy; clinical diagnosis involves ruling out other causes of dementia.
- Currently, there is no cure, and available medications offer only modest benefits.
Understanding the progressive nature of symptoms and the limitations of current diagnosis and treatment highlights the significant unmet need in Alzheimer's care.
Early symptoms like forgetting what one ate for breakfast, progressing to forgetting a spouse's name.
Key takeaways
- Alzheimer's disease is characterized by the buildup of beta-amyloid plaques outside neurons and tau tangles inside neurons, both contributing to neuronal dysfunction and death.
- The processing of amyloid precursor protein (APP) by different secretase enzymes determines whether soluble peptides or sticky amyloid-beta monomers are produced.
- Tau protein's normal function is to stabilize neuronal microtubules; its dysfunction in Alzheimer's leads to tangled aggregates and impaired cellular transport.
- Sporadic Alzheimer's is the most common form, with age being a primary risk factor, while familial Alzheimer's is rarer, early-onset, and caused by specific genetic mutations.
- Genetic factors like the APOE-e4 allele and mutations in PSEN-1/PSEN-2 genes significantly influence an individual's risk and the disease's progression.
- Symptoms of Alzheimer's are progressive, affecting memory, cognition, motor skills, and language over time.
- Current diagnostic methods rely on excluding other conditions, and effective treatments to halt or cure the disease are still lacking.
Key terms
DementiaAlzheimer's diseaseNeurodegenerative diseaseNeuronsAmyloid precursor protein (APP)Beta-amyloid plaquesTau proteinNeurofibrillary tanglesMicrotubulesSporadic Alzheimer'sFamilial Alzheimer'sAPOE-e4Amyloid angiopathy
Test your understanding
- What are the two primary pathological hallmarks of Alzheimer's disease, and where are they located within the neuron?
- How does the enzymatic cleavage of amyloid precursor protein (APP) lead to the formation of beta-amyloid plaques?
- What is the normal function of tau protein in a neuron, and how does its dysfunction contribute to Alzheimer's pathology?
- What is the difference between sporadic and familial Alzheimer's disease in terms of onset, prevalence, and underlying causes?
- Why is diagnosing Alzheimer's disease challenging, and what are the current limitations in its treatment?