Lecture 6 - BS3580

Alzheimer's Disease (AD) is a complex neurodegenerative disorder that leads to gradual and progressive mental deterioration, primarily affecting memory, cognitive functions, and the ability to perform daily activities. AD is the most prevalent cause of dementia, accounting for 50-75% of dementia cases globally, and poses significant challenges for individuals, families, and healthcare systems.

Epidemiology

AD is more prevalent in women than men, with a ratio of approximately 1.17:1, which may be attributed to women's longer life expectancy. In the UK, around 360,000 new cases of AD are diagnosed annually, translating to roughly 980 new cases daily and 40 new cases every hour. Worldwide, the number of individuals affected by Alzheimer's is estimated at 43.8 million, with approximately 850,000 of those living in the UK. The risk of developing Alzheimer's Disease doubles approximately every five years after the age of 60, with nearly 40% of individuals over 85 being affected.

Economic Impact

The economic burden of dementia in the UK is substantial, with estimated costs expected to rise from £34.7 billion to £94 billion by 2040. This increase will significantly impact healthcare systems, social care services, and unpaid family caregivers who provide crucial support to individuals living with AD. Understanding these costs is critical for policymakers to address the growing demand for resources in the coming decades.

Diagnosis of Alzheimer's Disease

Diagnosing Alzheimer's Disease can be challenging, as misdiagnosis occurs frequently. Research indicates that only 28% of patients are initially diagnosed correctly with AD. Key diagnostic features that healthcare providers look for include:

  • Gradual cognitive decline over time

  • Increasing difficulty in performing familiar tasks

  • Language problems, such as difficulty finding words or understanding conversations

  • Changes in mood or behavior, which may manifest as anxiety, depression, or irritability
    These features highlight the need for comprehensive assessments, including neuropsychological testing and imaging studies, to arrive at an accurate diagnosis.

Pathophysiology

AD is characterized by two primary pathological hallmarks: amyloid plaques and neurofibrillary tangles.

  • Amyloid plaques are aggregates primarily composed of beta-amyloid (A(\beta)) peptides, which accumulate outside neurons and are believed to disrupt cell function and lead to neuronal death.

  • Neurofibrillary tangles are intracellular aggregates formed by hyperphosphorylated tau protein. The accumulation of tau tangles within neurons is associated with synaptic dysfunction and cell loss.
    Research has shown that the formation of A(\beta) plaques is crucial in AD pathology, leading to subsequent cognitive decline.

APP and Amyloid Formation

The amyloid precursor protein (APP) plays a vital role in the formation of A(\beta) peptides. It is processed by different secretases to generate these peptides, which can proceed through two main pathways:

  • The amyloidogenic pathway, which involves both beta-secretase and gamma-secretase and leads to the generation of pathogenic A(\beta) peptides.

  • The non-amyloidogenic pathway, which utilizes alpha-secretase and produces non-amyloidogenic fragments.
    Mutations in the APP gene can increase the risk of developing AD by enhancing the production of the more toxic A(\beta)42 peptide.

Tau Pathology

Hyperphosphorylation of tau protein leads to its detachment from microtubules, resulting in instability of the neuronal cytoskeleton. The formation of tau tangles not only disrupts normal neuronal function but also contributes to neuronal loss and subsequent memory impairment, marking a critical aspect of the disease’s progression.

Genetic Factors

Alzheimer's Disease can be classified into two main types based on its onset:

  • Sporadic AD (late onset), which is significantly influenced by genetic factors, notably the presence of the ApoE4 allele, accounting for 40-60% of cases linked to genetic mutations.

  • Familial AD (early onset), linked to specific mutations in APP or presenilins, such as Presenilin 1, which often leads to earlier development of symptoms and a more aggressive disease course.
    Genetic testing and family history can help identify individuals at risk for familial AD.

Current Treatment Approaches

While there is currently no cure for Alzheimer's Disease, several treatment options are available:

  • Cholinesterase inhibitors (e.g., Donepezil, Rivastigmine, Galantamine) can improve cognitive function and overall quality of life for some patients by increasing acetylcholine levels in the brain, thus enhancing neuronal communication.

  • Memantine, an NMDA receptor antagonist, has been shown to limit excitotoxicity caused by excessive calcium influx into neurons, which can protect against cell death.

  • New medications, such as Aducanumab and Lecanemab, are designed to promote the clearance of A(\beta) plaques from the brain. While these have shown promise, results in cognitive improvement among patients have been mixed and further studies are ongoing.

Research Focus Areas

Current research is exploring various aspects of Alzheimer's Disease, including:

  • The role of soluble A(\beta) oligomers in affecting synaptic transmission and serving as early indicators of AD onset.

  • The biochemical pathways involved in the progression of AD, with a focus on tau pathology and the pathological role of amyloid plaques.

  • The potential influence of infections and inflammatory processes in the development of AD, as well as investigating dietary interventions such as ketogenic diets for their therapeutic benefits.

Conclusion

A comprehensive understanding of Alzheimer’s disease necessitates a multidisciplinary approach that encompasses epidemiology, genetics, pathophysiology, and therapeutic strategies. This highlights the critical need for early diagnosis, intervention measures, and ongoing research aimed at slowing the disease’s progression and improving the quality of life for those affected by AD.