**Core Concept**
Wilson's disease is a genetic disorder characterized by excessive accumulation of copper in the body, particularly in the liver, brain, and other organs. This accumulation leads to oxidative stress, inflammation, and ultimately, tissue damage. The disease is caused by mutations in the ATP7B gene, which encodes a copper-transporting P-type ATPase responsible for regulating copper levels in the body.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of Wilson's disease, where the accumulation of copper in the liver leads to the formation of toxic compounds, such as reactive oxygen species (ROS) and lipid peroxides. These toxic compounds damage liver cells, leading to liver dysfunction and cirrhosis. The ATP7B gene plays a crucial role in regulating copper levels by transporting excess copper into bile for excretion. Mutations in this gene disrupt this process, leading to copper accumulation.

**Why Each Wrong Option is Incorrect**

* **Option A:** Wilson's disease is characterized by copper deficiency.
- This is incorrect because Wilson's disease is actually characterized by copper accumulation, not deficiency.
* **Option B:** Wilson's disease is caused by mutations in the ATP7A gene.
- This is incorrect because Wilson's disease is caused by mutations in the ATP7B gene, not ATP7A.
* **Option C:** Wilson's disease primarily affects the kidneys.
- This is incorrect because Wilson's disease primarily affects the liver and brain, not the kidneys.

**Clinical Pearl / High-Yield Fact**
Wilson's disease is often referred to as "hepatolenticular degeneration" due to its effects on the liver and the brain's basal ganglia, leading to neurological symptoms such as tremors and dystonia.

**Correct Answer:** B. Wilson's disease is caused by mutations in the ATP7B gene.