## Core Concept
Gerstmann syndrome, also known as Gerstmann-Sträussler-Scheinker disease (GSS), is a rare, degenerative, and fatal brain disorder. It is one of the prion diseases, which are caused by misfolded proteins. A key feature of GSS is the accumulation of abnormal prion protein in the brain, leading to neuronal degeneration.

## Why the Correct Answer is Right
The characteristic features of Gerstmann syndrome include:
- **Cognitive decline**: A progressive decline in cognitive functions.
- **Cerebellar ataxia**: Problems with coordination and balance.
- **Pyramidal signs**: Indicative of upper motor neuron lesions, such as spasticity and weakness.
- **Personality changes**: Including apathy, depression, and anxiety.

## Why Each Wrong Option is Incorrect
- **Option A:** Cognitive decline is a core feature of Gerstmann syndrome, making it incorrect as an "EXCEPT" option.
- **Option B:** Cerebellar ataxia is another hallmark, characterized by difficulties with walking, balance, and coordination, making it incorrect as an "EXCEPT" option.
- **Option C:** Pyramidal signs are also present, indicating upper motor neuron involvement, which makes this option incorrect as well.

## Clinical Pearl / High-Yield Fact
A crucial point to remember about prion diseases like Gerstmann syndrome is that they are **not transmissible** in the traditional sense (e.g., through casual contact) but can be transmitted through certain medical procedures (e.g., corneal transplant) or contaminated surgical instruments. A classic clinical correlation is the association of these diseases with specific genetic mutations.

## Correct Answer Line
**Correct Answer: D.**