What Is Duchenne Muscular Dystrophy (DMD)?
Duchenne muscular dystrophy is a rare, progressive disorder that causes muscles to gradually weaken over time. It primarily affects muscles responsible for movement, breathing, and heart function.
The disease is genetic and occurs predominantly in males. Symptoms usually begin in early childhood and progressively worsen with age. As affected children grow, they may show signs such as developmental delay, walking on tiptoe, and increasing muscle weakness. Duchenne muscular dystrophy affects approximately one in every 3,600 male infants, making it the most common form of muscular dystrophy and one of the most severe inherited muscle diseases (myopathies).
Why Is It Called “Muscular Dystrophy”?
The term “muscular dystrophy” does not mean that muscles weaken due to poor nutrition. Instead, it refers to defects in the structure and repair mechanisms of muscle tissue itself. To understand why muscle degeneration occurs, it is first necessary to consider how healthy muscles maintain their strength.
Muscles rely on structural proteins to remain stable, and one of the most critical of these proteins is dystrophin. Dystrophin helps stabilize the muscle cell membrane and protects muscle fibers from damage during contraction. In Duchenne muscular dystrophy, mutations in the gene that encodes dystrophin prevent the body from producing this essential protein. As a result, muscle cell membranes become extremely fragile. Each movement causes microscopic tears, and because the muscle’s ability to repair itself is insufficient, muscle fibers gradually degenerate and are replaced by fat and connective tissue. Eventually, many individuals with DMD lose the ability to walk independently and must rely on a wheelchair (Figure 1).
Figure 1. A patient with Duchenne muscular dystrophy relies on a wheelchair
Where Does the Disease Begin, and Why Does It Primarily Affect Boys?
Duchenne muscular dystrophy is usually inherited within families and follows an X-linked recessive pattern of inheritance. In X-linked recessive conditions, the disease-causing gene is located on the X chromosome, and the condition develops only when there is no normal copy of the gene to compensate for the mutation. If an individual has two X chromosomes and only one carries the mutated gene while the other is normal, the disease typically does not manifest.
This explains why DMD predominantly affects boys. Males have one X chromosome and one Y chromosome, with the X chromosome inherited from the mother and the Y chromosome from the father. Females, in contrast, have two X chromosomes, one inherited from each parent.
Because boys possess only a single X chromosome, a mutation in the DMD gene on that chromosome will lead to the disease, as there is no second X chromosome to serve as a “backup” and compensate for the defect. Girls, however, usually have a second, unaffected X chromosome that can partially or fully compensate for the mutation, which is why they typically do not develop the disease.
As a result, most girls do not show symptoms or experience only very mild ones. However, they may be carriers of the condition. Carriers do not usually develop DMD themselves, but they carry the disease-causing gene and may pass it on to the next generation.
What Symptoms Does DMD Cause, and How Does It Affect Daily Life?
The symptoms of Duchenne muscular dystrophy progressively worsen over time. Individuals with DMD may experience increasing muscle weakness, joint stiffness, developmental delays—such as speaking their first words or sitting independently later than expected—easy fatigue, and a gradual loss of muscle mass. Muscle weakness significantly affects how a child walks and moves, often making it difficult to climb stairs, run, or jump. As the disease progresses, children may develop enlarged calves due to fatty infiltration (Figure 2), experience frequent falls (Figure 3), and rely on their hands to push against the ground or their legs when standing up, a compensatory movement known as Gowers’ sign (Figure 4). Walking on tiptoe (Figure 5) and a characteristic waddling gait are also common.
In addition to these features, the condition may lead to other physical changes, as depicted in the artwork. These include a protruding abdomen, weakened gluteal muscles, bent knees, thinning of the thighs, and unnatural positioning or movement of the shoulders and arms. Together, these symptoms affect not only mobility but also endurance, posture, and independence, shaping many aspects of daily life for individuals living with DMD.
Figure 2. Calf Muscle Enlargement
Figure 3. Frequent Falls
Figure 4. Using hands to push off the ground when standing up
Figure 5. Toe Walking