**Core Concept**
Menke's kinky (Steely) hair disease is a rare, inherited disorder that affects copper levels in the body, particularly in the brain, connective tissue, and hair. It is characterized by progressive neurological degeneration, sparse and coarse hair, and a distinctive "kinky" or "steely" appearance.

**Why the Correct Answer is Right**
Menke's kinky (Steely) hair disease is caused by mutations in the ATP7A gene, which encodes a copper-transporting ATPase. This enzyme plays a crucial role in regulating copper levels in the body by transporting it from the intestine to the bloodstream and from the bloodstream to other tissues. Defects in ATP7A lead to excessive loss of copper in the urine and impaired copper uptake by cells, resulting in copper deficiency and the characteristic symptoms of Menke's disease.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Menke's disease is not caused by a deficiency of the vitamin biotin.
**Option B:** This option is incorrect because Wilson's disease, not Menke's disease, is caused by a mutation in the ATP7B gene, which also regulates copper levels but in a different manner.
**Option C:** This option is incorrect because Menke's disease is not caused by a deficiency of the mineral zinc.

**Clinical Pearl / High-Yield Fact**
Menke's kinky (Steely) hair disease is a genetic disorder that affects copper levels in the body, leading to progressive neurological degeneration and distinctive physical symptoms.

**Correct Answer: C. A mutation in the ATP7A gene.**