Learn The BasicsThe primary sign of Duchenne muscular dystrophy (DMD) is progressive muscle weakness. The disease is caused by a mutation in the DMD gene, which is situated on the X chromosome and primarily affects boys.
This gene codes for dystrophin, a protein essential for maintaining muscle strength and protecting muscle cells from damage. The mutation in the DMD gene causes the production of dysfunctional dystrophin leading to muscle tissue breakdown with repetitive use. Eventually, this results in muscle wasting and replacement with scar tissue.
Signs and symptoms in children
The signs and symptoms of DMD, which appear in early childhood (usually between two to six years of age) include:
- Frequent falls
- Delayed motor development
- Difficulty getting up from a lying or sitting position
- Difficulty running, jumping, and climbing stairs
- Waddling gait
- Toe walking
- Enlarged calf muscles (pseudohypertrophy, due to fat and scar tissue replacing muscle fibers)
- Muscle pain and stiffness
- Delayed growth
- Learning difficulties
Boys with DMD have a distinctive way of standing up from the floor called Gower’s Maneuver in which they assume the hands-and-knees position and then climb to a stand by “walking” their hands progressively up their shins, knees, and thighs.
This may help doctors suspect DMD and conduct further tests to reach a final diagnosis.
Signs and symptoms in adults
As the disease progresses patients start to develop other symptoms and complications associated with the disease. These include:
- Cardiomyopathy or heart muscle disease
- Shortness of breath and breathing difficulties
- Short stature
- Scoliosis or sideways curvature of the spine
In the later stages of the disease, patients lose the ability to walk altogether and require a wheelchair for mobility.
They eventually go on to require a ventilator to assist with breathing as the diaphragm becomes too weak to allow for independent breathing.
Symptoms of cardiomyopathy
The symptoms of cardiomyopathy usually develop when patients are in their early teens and affect almost all patients by the time they are in their twenties.
They may include:
- Arrhythmia or an irregular heartbeat
- Shortness of breath
- Fatigue
- Edema (swelling in the legs and feet from fluid buildup)
These heart problems usually become worse quickly as the disease progresses, and in most cases, becomes life-threatening.
Intellectual disability
While intellectual impairment is seen in all patient with DMD, only 20-30% of patients have an intelligence quotient (IQ) of less than 70. Most patients have mild learning impairment and can attend a regular school, though they may need additional educational support.
The degree of intellectual impairment does not correlate with the severity of the disease severity.
Epilepsy is more common among patients with DMD compared to the general population.
Autism-like behavior has also been described, though this is not common.
Signs and symptoms in girls
Although DMD mostly affects boys, girls who are carriers of the faulty gene may also show some signs and symptoms of the disease.
These may include:
- Muscle pain and cramps with physical exertion
- Mild to moderate muscle weakness
- Cardiomyopathy
The mutation in the DMD gene causes the production of dysfunctional dystrophin leading to muscle tissue breakdown with repetitive use. Eventually, this results in muscle wasting and replacement with scar tissue.
Because females have two copies of the X chromosome, even if they inherit one faulty copy from their parents, they usually do not usually develop the symptoms of DMD as enough dystrophin protein can be made from the healthy gene situated on the other X chromosome. However, some female carriers may experience mild muscle weakness or heart-related symptoms due to an imbalance in how the X chromosomes are expressed in their cells.