Concept:
Wilson disease is a genetic disorder of copper metabolism. In this disease, copper is not properly excreted from the body.
Step 1: Normal copper metabolism.
Normally, excess copper is removed from the body through bile.
Step 2: What happens in Wilson disease?
In Wilson disease, copper accumulates in tissues because its excretion is defective.
Step 3: Organs affected.
Excess copper may accumulate mainly in:
• Liver
• Brain
• Eyes
Step 4: Clinical importance.
Copper accumulation can cause liver disease, neurological symptoms, and Kayser-Fleischer rings in the eyes.
Step 5: Final answer.
Therefore, Wilson disease is due to excess copper.
\[
\boxed{\text{Copper}}
\]