**Core Concept**
Wilson disease is a genetic disorder characterized by excessive accumulation of copper in the body, particularly in the liver, brain, and other organs. Treatment with chelating agents such as trientine and penicillamine aims to remove excess copper from the body.

**Why the Correct Answer is Right**
The goal of treatment is to maintain a low level of free serum copper to prevent further accumulation and toxicity. Free serum copper levels should be kept below 10-15 μmol/L (micrograms per liter) to prevent neurological symptoms and liver damage. This is achieved through regular monitoring and adjustment of medication doses. The chelating agents work by binding to copper ions in the blood, which are then excreted in the urine.

**Why Each Wrong Option is Incorrect**
**Option A:** Keeping free serum copper levels above 20 μmol/L can lead to worsening of neurological symptoms and liver damage.
**Option B:** There is no specific threshold for free serum copper levels in Wilson disease treatment, but maintaining levels below 10-15 μmol/L is generally recommended.
**Option C:** Free serum copper levels should not be kept below 0 μmol/L, as this would indicate a deficiency of copper, which is essential for various bodily functions.

**Clinical Pearl / High-Yield Fact**
To remember the goal of treatment in Wilson disease, the mnemonic "COPPER" can be used: Control accumulation, Observe for toxicity, Prevent neurological damage, Evaluate response to treatment, and Pursue regular monitoring.

**Correct Answer:** C. 10-15 μmol/L