In Duchenne muscular dystrophy (DMD), muscles weaken and degenerate over time. It mostly affects children assigned male at birth, but can sometimes affect children assigned female at birth who are carriers of the mutated gene. Muscular dystrophy, which affects the muscles, is the most common and severe type. DMD has no cure, but treatments can help manage the symptoms and improve the quality of life of people with the condition.
There is a mutation in a gene that produces a protein called dystrophin. Without dystrophin, muscle cells die and become damaged, resulting in muscle weakness and wasting.
DMD is caused by a mutation on the X chromosome, a sex chromosome that determines a person's biological sex. A person assigned to male at birth has one X chromosome and one Y chromosome, while a person assigned to female has two X chromosomes. Mutations in the DMD gene are inherited in an X-linked recessive pattern, which means:
In the case of a child assigned male at birth who inherits one X chromosome with the mutated gene from their mother, the child will have DMD, which is caused by the lack of another copy of the gene to produce dystrophin.
A child assigned female at birth who inherits one X chromosome with the mutated gene from either parent will be a carrier of DMD, but won't have the condition, because they have another copy of the gene that produces dystrophin. Due to random inactivation of one of their X chromosomes (a process called X-inactivation), some carriers may experience mild symptoms of DMD.
Children born male who inherit one X chromosome with the mutation from their father and one X chromosome without the mutation from their mother will not have DMD, but can carry the condition and pass it on to their children.
A child assigned female at birth who inherits two X chromosomes with the mutated gene from both parents will have DMD, but this is very rare.
About 30% of cases of DMD are not inherited, but are caused by new mutations that occur randomly in the egg or sperm cells of the parents or in the early development of the embryo.
The symptoms of DMD usually appear between the ages of 2 and 6, but can vary depending on the severity of the mutation and the amount of dystrophin produced by the cells. The symptoms of DMD include:
Muscle weakness and atrophy (loss of muscle mass) affecting the legs, pelvis, arms, neck, and other areas of the body, affecting walking, standing, sitting, climbing stairs, and other movements.
Enlarged calf muscles due to the accumulation of scar tissue and fat in the muscle fibers.
Frequent falls, waddling gait, toe walking, and difficulty maintaining balance.
Fatigue, shortness of breath, and reduced exercise tolerance due to the involvement of the respiratory and cardiac muscles.
Scoliosis (curvature of the spine), contractures (stiffening of the joints), and bone fractures due to the weakening of the skeletal muscles and bones.
Learning disabilities, cognitive impairment, speech and language delays, and behavioral problems due to the effects of the mutation on the brain and nervous system.
Cardiomyopathy (enlargement and weakening of the heart muscle), arrhythmias (irregular heartbeats), and heart failure due to the damage of the cardiac muscle cells.
By the time they are in their early teens, most people with DMD are unable to walk and have to use a wheelchair. Depending on the availability and effectiveness of treatments and the severity of the complications, people with DMD typically live between 20 and 30 years, but this can vary.
The diagnosis of DMD is based on the following tests and procedures:
A physical examination to assess the muscle strength, reflexes, and range of motion of the joints.
A blood test to measure the level of creatine kinase (CK), an enzyme that leaks from the damaged muscle cells into the bloodstream. A high level of CK indicates muscle damage and is a sign of DMD or other muscular dystrophies.
A genetic test to identify the mutation in the DMD gene and confirm the diagnosis. This test can also be used for prenatal diagnosis, carrier testing, and genetic counseling.
A muscle biopsy to take a small sample of the muscle tissue and examine it under a microscope. This test can show the absence or reduction of dystrophin in the muscle cells and rule out other causes of muscle weakness.
An electromyography (EMG) to measure the electrical activity of the muscles and nerves. This test can show the pattern and extent of muscle damage and dysfunction.
An electrocardiogram (ECG) to record the electrical signals of the heart and detect any abnormalities in the heart rhythm or function.
An echocardiogram (ECHO) to use sound waves to create an image of the heart and evaluate its structure and performance.
A pulmonary function test (PFT) to measure the lung capacity and airflow and assess the respiratory function.
Currently, there is no cure for DMD, but treatments can help slow down the progression of the disease, manage the symptoms, prevent or treat complications, and improve quality of life. DMD treatments include:
As well as corticosteroids, which reduce inflammation and delay muscle degeneration, exon-skipping drugs, which skip over the mutated part of the gene, gene therapy, which uses a viral vector to deliver a functional copy of the DMD gene to muscle cells, exon-skipping drugs, which partially restore dystrophin production. There is limited availability and effectiveness of these treatments due to their experimental nature.
Therapy that maintains muscle strength, flexibility, and function; prevents or delays contractures and scoliosis; and provides guidance on how to use assistive devices, such as braces, splints, and wheelchairs.
Occupational therapy, to help with the daily activities, such as dressing, eating, and bathing; and provide adaptive equipment, such as modified utensils, keyboards, and switches.
Speech therapy, to improve the speech and language skills; and provide augmentative and alternative communication (AAC) devices, such as speech-generating devices, tablets, and eye-gaze systems.
Provide speech therapy and augmentative and alternative communication (AAC) devices, such as tablets and eye-gaze systems, to improve speech and language skillss through a mask or a tracheostomy tube.
By providing mechanical ventilation, such as a BiPAP or CPAP machine, pressurized air is delivered to the lungs through a mask or a tracheostomy tube, to assist with breathing and prevent respiratory infectionsa pacemaker or a defibrillator, to regulate the heart rhythm and prevent sudden cardiac arrest.
A balanced and healthy diet is provided to prevent or treat nutritional deficiencies, obesity, constipation, and osteoporosis caused by reduced mobility and muscle weakness.
Psychological therapy, to provide emotional and mental support; and address the depression, anxiety, and stress that can affect the person with DMD and their family and caregivers.
Palliative care, to provide comfort and relief from the pain and symptoms; and improve the quality of life and dignity of the person with DMD and their family and caregivers.
Fortunately, some preventive measures can help reduce the risk of complications and improve the outcome of DMD, as it is a genetic condition inherited or caused by random mutations. These measures include:
Early diagnosis and intervention, to start the treatments as soon as possible and delay the disease progression and complications.
Regular follow-up and monitoring, to check the muscle, respiratory, cardiac, and bone health; and adjust the treatments as needed.
Immunization and infection prevention, to protect against the common infections, such as the flu and pneumonia, that can worsen the respiratory and cardiac function.
Exercise and physical activity, to maintain the muscle strength and function; and prevent the loss of bone density and the development of obesity.
Education and awareness, to learn about the condition and its management; and seek the support and resources from the healthcare providers, social workers, and advocacy groups.
