What Is Duchenne Muscular Dystrophy? Causes, Symptoms, and Treatment

Muscular dystrophies are a group of diseases that make the muscles of the body weaker over a period of time. The muscles become less flexible in this condition. Out of the nine types of muscular dystrophy, Duchenne muscular dystrophy is one of the most common.

The main characteristics of this medical condition are progressive degeneration of muscles and muscle weakness. Certain genes are present to control the function of the muscles and keep the body healthy, and any flaws in these genes can cause Duchenne muscular dystrophy. The disease usually affects boys, and its symptoms generally begin in early childhood. Children with this condition have a hard time walking, standing up, and climbing stairs. Eventually, they need wheelchairs to move around.

Children suffering from DMD may also have heart- and lung-related problems. There are therapies that can help ease the symptoms, and researchers are finding new ways to help patients cope with the condition. The outlook for this disease has positively changed over time. In the past few decades, children who were born with DMD did not have any chance of survival once they reached their teenage years. But today, with improvements in technology, they at least live well into their 30s, and some even live longer to their 40s or 50s.

What Are the Causes of Duchenne Muscular Dystrophy?

Genes in our cells carry information that the body needs to make proteins. With the help of these proteins, the body is able to carry out many different functions. DMD is caused by a flaw in one of the genes. Dystrophin is a protein that normally keeps the muscles strong and protects them from injury. In children suffering from DMD, the protein is broken. This medical condition is commonly seen in boys due to the inheritance of the DMD genes from their parents. Scientists call it a sex-linked disease because it is connected to the chromosomes that determine the sex of the child.

Sometimes, even people who do not have a family history of this disease might get it due to some flaw in their genes, which occurs on its own. However, such cases are quite rare.

The first person to describe Duchenne muscular dystrophy was a French neurologist named Guillaume Benjamin Amand Duchenne, after whom the disease was named. The condition was first described in the late 1860s. However, very little was known about the causes of muscular dystrophy until the 1980s. In 1986, MDA-supported researchers identified a specific gene on the X chromosome. A flaw in this gene would lead to DMD. The protein linked to this gene was identified in 1987 and this protein was named dystrophin. It was later concluded that the lack of this protein would make muscles become more fragile and easily damaged.

DMD has an X-linked recessive inheritance pattern. When the gene is passed on from the mother to the child, the unborn child can be affected. In such cases, the mother is known as a carrier of the gene. Mostly, DMD carriers have one normal dystrophin gene on one X chromosome and one abnormal dystrophin gene on the other X chromosome. A majority of carriers may not show signs or symptoms of the disease, but some do. The symptoms can be mild, such as mild skeletal muscle weakness or cardiac involvement. 

Symptoms of Duchenne Muscular Dystrophy

The initial signs of Duchenne muscular dystrophy can be observed before a child turns six. The primary muscles affected are those found in the hips, thighs, pelvic area, and shoulders. The skeletal muscles in the legs, trunk, and arms are also affected later on, and the calves become enlarged as well.

The disease can also damage the heart, lungs, and other parts of the body. The child may experience any of the following symptoms as they grow older:

• Scoliosis, or curved spine
• Shortened, tight muscles in the legs or contractures
• Severe headaches
• Problems while learning new things or when memorizing
• Shortness of breath or irregular breathing
• Sleepiness
• Trouble while concentrating on a particular thing

The condition is not regarded as painful, but the muscle problems can cause cramps. Some children with DMD have learning disorders and behavior problems. However, the intelligence of the child is not affected.

Signs and Symptoms of Duchenne Muscular Dystrophy

Children who suffer from DMD are often late walkers.

• Toddlers with DMD: Parents might notice enlarged calf muscles, known as pseudohypertrophy, or false enlargement. In this condition, the muscle tissues may contain scar tissue.

• Preschoolers with DMD: Children may seem to be clumsy and often fall once they start walking. They can also have difficulty climbing stairs or getting up from the floor.

• DMD at school age: By the time the child comes of school age, the child walks on his toes or waddles and falls often. Such children tend to stick out their bellies and pull their shoulders back in order to maintain balance. Even while raising their arms they face difficulty.

• 7–12 years old: By this age, many children with DMD use a wheelchair.

• Teenage years: Assistance or mechanical support may be needed for activities that involve the arms, legs, or trunk.

• Pain and sensations: In DMD, the muscles tend to deteriorate. Although not painful, some might experience cramps. Over-the-counter pain relievers can be taken to relieve pain. Duchenne muscular dystrophy does not directly affect the nerves, hence, all the senses are normal.

• Heart: Due to low amounts of dystrophin, the muscle layer of the heart weakens. This condition results in cardiomyopathy. In severe cases, the damage caused to the heart can be life-threatening, so the heart should be closely monitored.

• Respiratory function: Once the child reaches the age of ten, the muscles that help in the functioning of the lungs and diaphragm may weaken, which then leads to the lungs being less efficient when it comes to the movement of air. The child may show symptoms such as shortness of breath and problems related to poor respiratory function. These symptoms can cause mental dullness, difficulty concentrating, severe headaches, nightmares, and sleeping problems. If the respiratory muscles are weak, the child may have difficulties with coughing, which will lead to an increased risk of developing severe respiratory infections. In such cases, a simple cold can easily progress to pneumonia.

Learning and Development

About a third of boys suffering from DMD have certain kinds of learning disabilities. A few may even have mental retardation. Studies have revealed that dystrophin abnormalities in the brain can cause subtle effects on behavior and cognition. This kind of learning behavior is identified in three general areas: emotional interaction, attention focusing, and verbal learning/memory.

An evaluation of the child by a pediatric neuropsychologist should be done if the child is suspected of having a learning disability. If a child is diagnosed with a learning disability, educational and psychological interventions should be started right away. Exercises and techniques that will help improve certain areas may be recommended by a specialist. The school may also help by providing special aid with learning.

Diagnosis of Duchenne Muscular Dystrophy

The following tests are requested if the doctor suspects DMD:

• Blood test: This test requires a sample of blood. The blood sample is used to test for creatine kinase, which is an enzyme released by the muscles if they get damaged. A higher level of creatine kinase could indicate DMD.

• Gene tests: A blood sample is taken and then used to check for any dystrophin changes. Females can undergo genetic testing to identify whether or not they are carriers of the gene.

• Muscle biopsy: A tiny piece of muscle is removed with the help of a needle. This muscle sample is then examined under a microscope to identify low levels of the dystrophin protein. This protein is usually missing in people suffering from DMD.

What Are the Treatment Options for Duchenne Muscular Dystrophy?

Currently, there is no cure for Duchenne muscular dystrophy. However, there are certain medications and therapies available that can help reduce symptoms and protect the muscles. These drugs can also keep the heart and lungs healthy.

• Exondys 51 (eteplirsen): This drug comes in the form of an injection, which is approved by the FDA to treat DMD. Individuals with a specific type of gene mutation leading to DMD can be treated with this medication. However, this drug has certain side effects, such as balance problems and vomiting.

• Emflaza (deflazacort): This oral corticosteroid was recently approved by the FDA to treat DMD. It is also the first approved corticosteroid for the treatment of DMD. It helps patients retain muscle strength and maintain their ability to walk. The side effects of this drug include puffiness, weight gain, and increased appetite.

• Prednisone: This drug is also a corticosteroid, which slows down muscle damage. Children who are on this medication are able to walk for many years compared to those who do not take the drug. It also helps the heart and lungs to function better.

• Cardiologist: Since DMD can affect the heart, it is important to see a cardiologist once every two years for a check-up until the age of ten, and also one more year after that. Girls and women with DMD should also regularly visit a cardiologist, because, if they are carriers of the gene, they have an increased risk of heart-related problems. A regular visit to a cardiologist will help detect any problems in their late teens or early adulthood.

• Surgery: To fix shortened muscles, surgery may be helpful. Surgery might also fix problems such as straightening of the spine and lung and heart problems.

• Other medications: There are some blood pressure medications that can help provide protection against heart muscle damage.

Taking Care of a Child with DMD

A treatment plan for DMD needs to be followed, and you should know what works best for your child to help them live an active life.

• Stand and walk technique: Stand and walk as much as possible. This will help the body to stay upright. Being upright will make the bones strong as well as straighten the spine. To make standing and getting around easier, braces or standing walkers can be used.

• Eat right: There is no special diet that should be followed for people with DMD. Healthy foods will help prevent constipation and weight problems. To decide the right nutrients for your child, consult a dietitian so that your child gets the right balance of nutrients and daily caloric intake. See a specialist if your child has trouble swallowing.

• Stay active: To keep the muscles limber, exercises and stretches should be done. This will also make your child feel better. With the help of a physical therapist, you will learn to teach your child how to exercise without overdoing it.

• Support: Contact family members living with DMD. Look out for a local support group for DMD. Explore and take part in online discussion boards. If required, talk to a counselor or psychologist.

Outlook 

The muscles tend to become weaker as the child gets older. Due to this weakness, the child may not be able to walk. By the time the child is 12 years old, a wheelchair may be required to help them move around.

Due to newer technologies, the outlook of this condition is better. In the past, children with DMD used to live only until their teens. Researchers are looking for new and better ways to treat the DMD-causing gene. The outlook might improve even more as years pass by. In 2014, European officials approved the drug Translarna (ataluren) to treat the genetic cause of DMD. More gene therapies will soon be available in the U.S.

Status of Research

MDA-supported researchers are studying several exciting ways and strategies to deal with DMD. They include gene therapy, exon skipping, stop codon read-through drugs, and gene repair. There are some human clinical trials underway for these strategies as well.

Extensive research is conducted to gain understanding on the causes of the muscle dysfunction in DMD. Research is also ongoing to use this understanding in making effective medications and treatments for the disease. The FDA is evaluating multiple therapies for approval. In DMD, the protein dystrophin is missing, which makes the body more susceptible to injury. It then leads to muscle loss and weakness. Scientists are trying hard to develop complementary therapies that can replace dystrophin. Such therapies could protect the muscles from injury and promote muscle repair and growth. Hopefully, these potential therapies can be used for maximum benefit. Research in the following areas is being done:

• Driving muscle growth
• Inserting a new dystrophin gene
• Accelerating muscle repair 
• Controlling the way genetic instructions are read by the cells
• Muscle protection from damage
• Blocking muscle fibrosis
• Increasing the blood flow to the muscles
• Protecting a heart that is dystrophin deficient
• Fighting muscle inflammation

Possible complications include:

• Cardiomyopathy
• Congestive heart failure
• Deformities
• Heart arrhythmia
• Mental retardation
• Pneumonia
• Respiratory failure
• Decreased mobility and ability to take care of oneself

Prevention

If you suspect a family history of DMD, seek genetic counseling. During pregnancy, genetic studies are accurately done to detect DMD.