**Question:** Duchnne's muscular dystrophy –

A. X-linked recessive inheritance
B. Symptoms appearing in early childhood
C. Muscle weakness and wasting
D. Defective glycogen synthesis

**Correct Answer:**

**Core Concept:**

Duchenne muscular dystrophy (DMD) is a severe genetic disorder characterized by the progressive loss of muscle function and strength. It is caused by mutations in the **DMD gene** located on the X-chromosome, which encodes the protein dystrophin. **Dystrophin** is a structural protein that helps maintain the integrity of muscle fibers and prevents muscle damage during contraction and relaxation. The absence of dystrophin in DMD leads to muscle degeneration, inflammation, and replacement by fatty and fibrous tissue.

**Why the Correct Answer is Right:**

Duchenne muscular dystrophy is an **X-linked recessive disorder**, meaning that it is inherited from an affected mother to her male children. In this case, the mother is usually asymptomatic due to the possibility of having a functional copy of the DMD gene on her other X-chromosome. Boys with DMD will have only the mutated gene, resulting in the absence of dystrophin and the progression of the disease.

**Why Each Wrong Option is Incorrect:**

A. Mutation in the DMD gene causing Duchenne muscular dystrophy is **not** related to defects in glycogen synthesis (option D). Glycogen synthesis has no direct connection to the disease, while DMD focuses on dystrophin deficiency.

B. Symptoms in Duchenne muscular dystrophy typically appear during early childhood, typically before the age of 6 years (option B). This is a key feature of the disease and distinguishes it from other muscular dystrophies.

C. Muscle weakness and wasting are indeed present in Duchenne muscular dystrophy (option C). However, this option is too broad and does not differentiate the correct answer from the wrong options.

**Clinical Pearl:**

Understanding the genetics and clinical features of Duchenne muscular dystrophy is essential for diagnosing and managing patients affected by this condition. Early recognition and intervention can significantly improve the quality of life and slow the progression of the disease.