**Core Concept**
Prion-associated diseases are a group of rare, fatal neurodegenerative disorders caused by misfolded proteins called prions. These diseases are characterized by the accumulation of abnormally folded prion proteins in the brain, leading to neuronal damage and death.

**Why the Correct Answer is Right**
Prion diseases are a specific group of conditions that are transmitted through the misfolding of proteins. They are distinct from other neurodegenerative diseases such as Alzheimer's, Parkinson's, and Huntington's, which are caused by different mechanisms. The correct answer is one of the options that is not a prion-associated disease.

**Why Each Wrong Option is Incorrect**
**Option A:** Bovine spongiform encephalopathy (BSE), also known as mad cow disease, is a prion-associated disease caused by the consumption of contaminated beef products. It is a classic example of a prion disease.

**Option B:** Creutzfeldt-Jakob disease (CJD) is a human prion disease characterized by rapid onset of dementia, ataxia, and myoclonus. It is a prion-associated disease that can be sporadic, inherited, or acquired through medical procedures.

**Option C:** Gerstmann-Sträussler-Scheinker disease (GSS) is a rare, autosomal dominant prion disease that affects the cerebellum and is characterized by ataxia, dementia, and myoclonus. It is a prion-associated disease.

**Option D:** Alzheimer's disease is a neurodegenerative disorder characterized by the accumulation of amyloid-beta plaques and tau tangles in the brain. It is not a prion-associated disease, but rather a distinct entity with a different underlying pathophysiology.

**Clinical Pearl / High-Yield Fact**
Remember that prion diseases are unique in their transmission mechanism, which involves the misfolding of proteins rather than infectious agents. This is a key distinction from other neurodegenerative diseases.

**Correct Answer:** D. Alzheimer's disease.