True about aetiopathogenesis of Alzheimers disease-a) Absence of tau proteinb) Involvement of Apolipoprotein Ec) Preseneline-1and 2 involved d) Mutation in chromosome 21e) Preseneline 2 is not involved
**Core Concept**
Alzheimer's disease is a complex neurodegenerative disorder characterized by the accumulation of amyloid-beta plaques and tau protein tangles in the brain, leading to neuronal damage and cognitive decline. The pathogenesis involves a multifaceted interplay between genetic, environmental, and molecular factors.
**Why the Correct Answer is Right**
The correct answer, **C. Preseneline-1 and 2 involved**, is correct because mutations in the presenilin-1 (PSEN1) and presenilin-2 (PSEN2) genes are associated with early-onset familial Alzheimer's disease. These genes encode for proteins that are involved in the processing of amyloid precursor protein (APP) to produce amyloid-beta, a key component of the amyloid plaques found in Alzheimer's disease. The mutations lead to increased production or reduced clearance of amyloid-beta, contributing to the pathogenesis of the disease.
**Why Each Wrong Option is Incorrect**
* **Option A:** Absence of tau protein - This is incorrect because tau protein is actually a key component of the neurofibrillary tangles found in Alzheimer's disease. Tau protein plays a crucial role in maintaining the structure and stability of microtubules, and its abnormal phosphorylation and aggregation contribute to neurodegeneration.
* **Option B:** Involvement of Apolipoprotein E - While Apolipoprotein E (APOE) is associated with Alzheimer's disease, it is not a primary cause of the disease. APOE is involved in lipid metabolism and has been linked to increased risk of late-onset Alzheimer's disease, but it is not directly involved in the pathogenesis.
* **Option D:** Mutation in chromosome 21 - This is incorrect because while chromosome 21 is involved in Alzheimer's disease, the primary mutation associated with the disease is the APP gene, which is located on chromosome 21. However, the mutation in the APP gene itself is not the primary cause of the disease.
* **Option E:** Preseneline 2 is not involved - This is incorrect because presenilin-2 (PSEN2) is indeed involved in the pathogenesis of Alzheimer's disease. Mutations in the PSEN2 gene have been identified in cases of early-onset familial Alzheimer's disease.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that Alzheimer's disease is a complex disorder with multiple genetic and environmental risk factors. While presenilin mutations are associated with early-onset familial Alzheimer's disease, the majority of cases are late-onset and involve a combination of genetic, lifestyle, and environmental factors.
**Correct Answer:** C. Preseneline-1 and 2 involved