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What Is Duchenne Muscular Dystrophy?
By Get Science Staff: This article originally published on Get Science
Muscular dystrophies are a debilitating group of illnesses that not only rob children of their ability to move properly, but can dramatically shorten their lives.
They are caused by a genetic defect that lead to weakness and degeneration in the muscles. Duchenne muscular dystrophy (DMD) is the most common type of muscular dystrophy and occurs mostly in boys.
About 15 out of every 100,000 males in the United States between the ages of 5 and 24 were reported in 2007 to have either DMD or a less severe form known as Becker muscular dystrophy (BMD), according to the U.S. Centers for Disease Control and Prevention.
The symptoms often begin to appear when they are toddlers
The symptoms of DMD usually appear between the ages of 3 and 5 – almost always in boys, but in rare cases in girls.
Children with DMD often start walking later than normal, and toddlers sometimes have enlarged calf muscles because the muscle tissue is abnormal and may contain scar tissue, according to the Muscular Dystrophy Association (MDA).
Toddlers with DMD may have difficulty running, climbing stairs or standing up, and may fall often, according to the MDA. By the time they enter school, children with DMD may walk on their toes or the balls of their feet with a waddling gait and some children may also have trouble raising their arms. Many children with DMD begin using a wheelchair sometime between ages of 7 and 12.
As the disease progresses, a child may also experience serious heart and lung conditions.
DMD is caused by the lack of a key protein
DMD is caused by an absence of a protein called dystrophin that helps keep muscle cells healthy. Dystrophin is one of the proteins in skeletal and cardiac muscles that strengthen muscle fibers and protect them as those fibers contract and lengthen . "The lack of dystrophin results in muscle damage and progressive loss of motor function as well as pulmonary and cardiac function," says Michael Binks, MD, Vice President in Pfizer's Rare Disease Research Unit in Kendall Square, Cambridge, Mass.
DMD is found primarily in boys because the defective gene is carried on the X chromosome – one of the chromosomes that determines the baby’s sex. Because a girl has two sets of X chromosomes, whereas a boy has an X chromosome and a Y chromosome, there’s less of a chance the defective gene will be expressed in a girl . That’s because even if a girl inherits a defective gene on one X chromosome, the gene on the other, unaffected X chromosome can take over, whereas a boy who inherits the defect on his one and only X chromosome has no backup gene, so to speak.
There are many steps to diagnosing DMD
If a parent notices delays in developmental milestones such as walking and running, there are a number of ways a doctor can test for DMD , including:
A blood test: This measures an enzyme called creatine kinase, which is released by the muscles when they are damaged. A high creatine kinase level could be an indication that a child may have DMD.
A genetic test: This tests for the flaw in the dystrophin gene itself.
A muscle biopsy: The doctor takes a small sample of the muscle using a needle and studies it under a microscope.
DMD treatments have boosted life expectancy
There is no cure for DMD yet, but the life expectancy for people with DMD has increased in recent years, with many people surviving into their early 30s.
This is primarily thanks to advances in heart and lung care and physical therapy regimens that can improve the function of the heart and lungs while also slowing the damage to muscle. These treatments can help some patients to continue walking for longer as well as maintain their independence.
Despite the gravity of a DMD diagnosis for a child, the outlook for a child living with this disorder has improved in recent years, with advancements in treatments, including drugs specifically targeting the gene responsible for the disorder.
"In DMD, there have been numerous clinical studies conducted in the past decade that have greatly improved our understanding of the course of this disease and it is very exciting to see a variety of therapeutic approaches in clinical development with potential to transform the outlook for these children," says Binks.