Muscular dystrophy is a group of genetic diseases that cause progressive muscle weakness and loss of muscle mass. There are nine recognized types, each caused by mutations in different genes, but they share a common problem: the proteins that protect muscle fibers during contraction are missing or defective, so muscles break down faster than the body can repair them.
How Muscle Breakdown Happens
Healthy muscle cells rely on a protein called dystrophin to survive the stress of repeated contractions. Dystrophin acts like an internal shock absorber, linking the structural skeleton inside each muscle fiber to a protective complex on its outer membrane. This connection stabilizes the membrane every time the muscle contracts and relaxes.
When dystrophin is missing or malformed, the outer membrane of the muscle cell becomes fragile. Normal movements that a healthy muscle handles easily cause tiny tears in the membrane of a dystrophin-deficient one. The body tries to repair the damage, but over time the cycle of tearing and incomplete repair replaces muscle tissue with scar tissue and fat. That’s why muscles in people with muscular dystrophy gradually lose their ability to generate force, even though the muscles may initially look normal or even enlarged.
The Nine Major Types
Each type of muscular dystrophy affects different muscle groups, appears at different ages, and progresses at different rates.
Duchenne (DMD) is the most common and severe form. Symptoms usually appear before age 5, starting with weakness in the upper legs and upper arms. About 1 in every 5,000 boys born is diagnosed with DMD. It almost exclusively affects males.
Becker (BMD) involves the same gene as Duchenne but produces a partially functional version of dystrophin rather than none at all. Symptoms appear later, sometimes not until adulthood, and progress more slowly. The same upper leg and upper arm muscles are affected first.
Myotonic dystrophy (DM) is the most common form in adults, typically appearing between ages 10 and 30, though onset can range from birth to age 70. It affects the face, neck, arms, hands, hips, and lower legs, and it also causes difficulty relaxing muscles after contraction.
Limb-girdle (LGMD) covers a large group of subtypes that weaken the muscles around the shoulders and hips. Onset varies widely from childhood to adulthood depending on the specific subtype. Facioscapulohumeral (FSHD) usually begins in young adulthood and first affects the face, shoulders, and upper arms. Congenital (CMD) is present at birth or early infancy, affecting the neck, upper arms, upper legs, and sometimes the lungs.
Distal dystrophy appears in adulthood and starts in the hands, feet, and lower limbs. Oculopharyngeal (OPMD) typically begins after age 40, causing weakness in the eyes and throat that leads to drooping eyelids and difficulty swallowing. Emery-Dreifuss (EDMD) starts in childhood, affecting the upper arms, lower legs, and heart, along with stiffness in the elbows, ankles, and neck.
How It’s Inherited
Duchenne and Becker muscular dystrophy follow an X-linked recessive inheritance pattern, which is why they overwhelmingly affect boys. The dystrophin gene sits on the X chromosome. Males have only one X chromosome, so a single mutated copy is enough to cause the disease. Females have two X chromosomes, so a working copy on the second X typically compensates for a defective one on the first.
Women who carry one mutated copy are called carriers. They usually don’t develop full-blown disease, but some experience mild muscle weakness, cramping, or an increased risk of heart problems. A carrier mother has a 50% chance of passing the mutation to each child. Fathers with DMD cannot pass the trait to their sons (since sons inherit their father’s Y chromosome, not his X), but all of their daughters will be carriers.
Not every case is inherited. A significant number of Duchenne cases result from new, spontaneous mutations, meaning there’s no family history of the disease.
Other types of muscular dystrophy follow different inheritance patterns. Myotonic dystrophy and some forms of limb-girdle dystrophy are autosomal dominant, meaning a single copy of the mutated gene from either parent can cause disease. Some limb-girdle subtypes are autosomal recessive, requiring a mutated gene from both parents.
Early Signs and Symptoms
In Duchenne, parents often notice that a child is slower to walk, falls frequently, or has difficulty running and climbing stairs. One of the earliest and most characteristic signs is the way a child gets up from the floor. Rather than standing up normally, children with proximal muscle weakness will roll onto their stomach, get on all fours, and then “walk” their hands up their own thighs to push themselves upright. This maneuver, first described in 1879 by neurologist William Gowers, reflects weakness in the pelvic and thigh muscles that normally power standing.
Before that classic pattern becomes obvious, subtler changes appear: a wider-than-normal stance, walking on tiptoes, and an exaggerated curve in the lower back to compensate for weakened hip muscles. Another early clue is calf muscles that look unusually large. This isn’t extra muscle but rather muscle tissue being replaced by fat and scar tissue, a process called pseudohypertrophy.
In adult-onset types like myotonic or facioscapulohumeral dystrophy, early symptoms are different. Difficulty whistling, inability to drink through a straw, or trouble raising the arms overhead may be the first things someone notices.
Diagnosis
When muscular dystrophy is suspected, a blood test measuring creatine kinase (CK) is typically the first step. CK is an enzyme that leaks out of damaged muscle cells into the bloodstream. In healthy individuals, CK levels fall between roughly 35 and 232 units per liter. In Duchenne muscular dystrophy, levels are 10 to 100 times higher than normal, often reaching into the thousands. Elevated CK confirms that muscle damage is occurring but doesn’t pinpoint the cause.
Genetic testing provides a definitive diagnosis. Modern testing panels use next-generation sequencing to analyze the entire coding region of genes associated with muscular dystrophy. The process typically starts with deletion and duplication analysis, since large deletions in the dystrophin gene account for the majority of Duchenne and Becker cases. If no deletion is found, full gene sequencing follows to identify smaller mutations. Any significant findings are confirmed through a second, independent round of testing to ensure accuracy.
Heart and Lung Complications
Muscular dystrophy doesn’t only affect the muscles you use to walk and lift. The heart is a muscle, and the diaphragm and rib cage muscles that power breathing are skeletal muscles. As the disease progresses, both systems come under threat.
Cardiac involvement ranges from minor electrical rhythm changes to full-blown dilated cardiomyopathy, where the heart muscle stretches and weakens until it can no longer pump blood efficiently. Depending on the type and subtype of muscular dystrophy, anywhere from 17% to 50% of patients develop some degree of heart dysfunction. Regular heart monitoring with echocardiograms is a standard part of long-term care.
Respiratory decline follows a parallel track. As the muscles that expand the chest weaken, lung capacity drops. Some patients eventually retain too much carbon dioxide because they can’t exhale forcefully enough, particularly during sleep. Yearly lung function testing and sleep studies help catch this decline early. Many patients eventually benefit from non-invasive ventilation, a mask-based breathing support used especially at night, which can significantly extend both comfort and survival.
Treatment Options
There is no cure for muscular dystrophy, but treatment has improved dramatically. Corticosteroids remain the backbone of Duchenne management, slowing muscle breakdown and helping children maintain the ability to walk for additional years.
Gene therapy has reached clinical use. In 2023, the FDA approved a gene therapy called Elevidys for Duchenne muscular dystrophy. It delivers a shortened, functional version of the dystrophin gene into the body through a single intravenous infusion. The therapy produces a mini-dystrophin protein that’s about one-third the size of the full protein but retains key protective functions. It is approved for individuals aged 4 and older with a confirmed DMD gene mutation. Side effects observed in clinical studies included vomiting, nausea, liver injury, fever, and low platelet counts.
Beyond medications, physical therapy and stretching help maintain flexibility and slow the development of joint contractures. Braces and orthotics can support weakened limbs. As the disease progresses, powered wheelchairs, breathing support devices, and cardiac medications become part of daily management. The goal at every stage is to preserve function, prevent complications, and maintain quality of life.
Life Expectancy
Life expectancy varies enormously depending on the type of muscular dystrophy. Becker and facioscapulohumeral dystrophy often allow a near-normal lifespan. Duchenne, the most severe form, has historically been associated with much shorter survival, but that picture is changing.
A large meta-analysis found that the overall median life expectancy for Duchenne is 22 years, but that number masks a significant trend. For patients born before 1970, median survival was 18.3 years. For those born between 1970 and 1990, it rose to 24 years. For those born after 1990, median survival reached 28.1 years. That improvement reflects better respiratory care, cardiac management, and steroid use rather than any single breakthrough.
Survival probabilities at different ages paint a more detailed picture. At age 10, survival is nearly 100%. By age 20, roughly 60% of patients are alive. By age 30, about 26% survive, and by 40, about 13%. The mortality rate has dropped steeply across generations: among patients aged 25 to 30, 265 out of every 1,000 born before 1970 died each year, compared to just 28 per 1,000 for those born after 1990. With gene therapy and other emerging treatments now entering clinical practice, outcomes for children diagnosed today are expected to continue improving.