**Question:** In Alzheimer’s disease, plaque is made up of:

A. Amyloid-beta peptide
B. Tau protein
C. Both A and B
D. Other proteins

**Core Concept:** Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the presence of extracellular amyloid plaques and intracellular neurofibrillary tangles in the brain. These pathological hallmarks lead to progressive cognitive decline and memory loss.

**Why the Correct Answer is Right:** Alzheimer's plaques are mainly composed of an amyloid-beta peptide, specifically the 42-amino acid version (Aβ42). This peptide is derived from the amyloid precursor protein (APP) through a process involving β- and γ-secretase enzymes. The accumulation of Aβ42 leads to the formation of extracellular plaques, which disrupt neuronal communication and contribute to neuronal death, ultimately causing cognitive impairment.

**Why Each Wrong Option is Incorrect:**

A. Alzheimer's plaques do contain some tau protein, particularly the hyperphosphorylated form (phosphorylated tau). However, the major component is the amyloid-beta peptide.
B. Tau protein is primarily associated with neurofibrillary tangles, not plaques.
C. While tau protein is present in Alzheimer's disease, it is not the primary component of plaques.
D. Alzheimer's plaques consist primarily of amyloid-beta peptide, not other proteins.

**Clearing Up Confusions:**

- Alzheimer's disease is often mistaken for vascular dementia due to their similar cognitive symptoms. However, Alzheimer's disease is characterized by extracellular plaques and neurofibrillary tangles, while vascular dementia results from ischemic lesions in the cerebral vasculature.
- The presence of Alzheimer's plaques is a defining feature of the disease, distinguishing it from other forms of dementia.

**Clinical Pearls:**

- Alzheimer's disease is a heterogeneous group of disorders, and the presence of plaques and tangles is essential for the diagnosis.
- Treatments targeting amyloid-beta peptide, such as monoclonal antibodies, are currently under development and show promise in reducing plaque burden in patients with mild to moderate Alzheimer's disease.

**Correct Answer:** C. Both A and B

**Why the Correct Answer is Right:** As mentioned, Alzheimer's disease is a heterogeneous group of disorders characterized by extracellular amyloid-beta plaques and intracellular neurofibrillary tangles. Both amyloid-beta peptide (option A) and tau protein (option B) are involved in Alzheimer's disease. The primary component is amyloid-beta peptide in the plaques, while tau protein forms the neurofibrillary tangles.

**Why Each Wrong Option is Incorrect:**

- Option A: Tau protein is present in Alzheimer's disease, but its role is confined to neurofibrillary tangles, not plaques.
- Option B: Tau protein is present in Alzheimer's disease, but plaques are primarily composed of amyloid-