**Core Concept**
Duchenne muscular dystrophy (DMD) is a genetic disorder characterized by progressive muscle degeneration and weakness. It is caused by an absence of **dystrophin**, a protein that helps keep muscle cells intact. This condition is inherited in an X-linked recessive pattern.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of DMD, which involves the lack of **dystrophin**. This leads to muscle cell damage and necrosis, resulting in muscle weakness and wasting. The **dystrophin** gene is located on the X chromosome, which explains the X-linked recessive inheritance pattern.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not relate to the primary cause of DMD.
**Option B:** This option is incorrect because it is not a characteristic of DMD.
**Option C:** This option is incorrect because it is not related to the **dystrophin** protein.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that DMD typically presents in early childhood, with symptoms such as delayed walking and muscle weakness.

**Correct Answer:** D. X-linked recessive disorder