Duchenne muscular dystrophy

Other Names: Muscular dystrophy, Duchenne; DMD; Muscular dystrophy, pseudohypertrophic progressive, Duchenne type

Duchenne muscular dystrophy (DMD) is a genetic condition that affects the muscles, leading to muscle wasting that gets worse over time. DMD occurs primarily in males, though in rare cases may affect females.

Drawing of 7-year-old boy with Duchenne muscular dystrophy. There is excessive development of the lower limbs (pseudohypertrophy), and thinness of the arms. In the figure on the right, lumbar hyperlordosis is visible.

cause

DMD is caused by genetic changes (DNA variants) in the DMD gene. Different DNA variants in the DMD gene can cause a spectrum of disorders known as dystrophinopathies. The dystrophinopathies can range from very mild symptoms to the more severe symptoms seen in people with DMD. Other dystrophinopathies include Becker muscular dystrophy (BMD) and DMD-associated dilated cardiomyopathy (DCM).

Signs and symptoms

The symptoms of DMD include progressive weakness and loss (atrophy) of skeletal and heart muscles. Early signs of DMD may include delayed ability to sit, stand, or walk and difficulties learning to speak. Muscle weakness is usually noticeable in early childhood. Most children with DMD use a wheelchair by their early teens. Heart and breathing problems also begin in the teen years and lead to serious, life threatening complications.

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. 80%-99% of people have these symptoms

• Calf muscle hypertrophy(Increased size of calf muscles)
• Cardiomyopathy(Disease of the heart muscle)
• Cognitive impairment(Abnormality of cognition)
• Delayed speech and language development(Deficiency of speech development)
• Elevated serum creatine kinase(Elevated blood creatine phosphokinase)
• Flexion contracture(Flexed joint that cannot be straightened)
• Global developmental delay
• Motor delay
• Progressive muscle weakness
• Proximal muscle weakness(Weakness in muscles of upper arms and upper legs)
• Respiratory insufficiency(Respiratory impairment)
• Scoliosis
• Skeletal muscle atrophy(Muscle degeneration)
• Specific learning disability
• Waddling gait

Inheritance

X-linked recessive inheritance

DMD is inherited in an X-linked recessive pattern and may occur in people who do not have a family history of DMD. X-linked means that the gene for the condition is located on the X-chromosome, one of the sex chromosomes. In males (who have only one X chromosome), one altered copy of the gene is enough to cause the condition. X-linked recessive conditions affect males much more frequently than females. Females, who have one altered gene, are called carriers. While, most female carriers have no signs or symptoms of the condition, in rare cases, female carriers may experience some mild signs or symptoms.

A female who carries one X-linked gene alteration has a 50% or 1 in 2 chance of having a son with the condition and a 50% chance of having a daughter who is also a carrier. A male with an X-linked recessive condition cannot pass on the disorder to his sons, but all of his daughters will be carriers.

Sometimes a male child is the first person in a family with the condition. In this case, the gene alteration may have been inherited from the mother, or the alteration may have occurred by chance for the first time in the child (de novo).

Diagnosis

Duchenne muscular dystrophy (DMD) is diagnosed in young boys based on clinical examination, signs and symptoms, family history, and genetic testing. Blood tests looking for increased levels of certain special proteins called muscle enzymes are used to check for muscle damage. Creatine kinase (CPK-MM) levels in the bloodstream are extremely high. An electromyography (EMG) shows that weakness is caused by destruction of muscle tissue rather than by damage to nerves. Tests used for diagnosis of DMD are

• DNA test
• Muscle biopsy
• Prenatal tests

Treatment

There is no known cure for Duchenne muscular dystrophy (DMD). Treatment is based on controlling the symptoms of DMD and related complications caused by severe progressive muscle weakness and loss. Medications (such as steroids) may improve the strength and function of muscles. Additional medications are available for people with DMD with a specific DNA variant. These can help improve muscle strength and function. An enlarged, weakened heart (dilated cardiomyopathy) may be treated with medications, but in severe cases, a heart transplant may be necessary. Assistive devices for breathing difficulties may be needed, especially at night and as the disease progresses. The medication(s) listed below have been approved by the Food and Drug Administration (FDA) as orphan products for treatment of this condition

• Deflazacort (Brand name: Emflaza) deflazacort (Emflaza) was approved for the treatment of Duchenne Muscular Dystrophy in patients 5 years of age and older.
• Eteplirsen (Brand name: Exondys 51) eteplirsen (Exondys 51) was approved for the treatment of Duchenne muscular dystrophy (DMD) in patients who have a confirmed mutation of the DMD gene that is amenable to exon 51 skipping.
• Golodirsen (Brand name: Vyondys 53) golodirsen (VYONDYS 53) was approved for the treatment of Duchenne muscular dystrophy (DMD) in patients who have a confirmed mutation of the DMD gene that is amenable to exon 53 skipping.

NIH genetic and rare disease info

• NIH info on Duchenne muscular dystrophy

Duchenne muscular dystrophy is a rare disease.

Duchenne muscular dystrophy Resources
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