If you or someone you love is living with Duchenne muscular dystrophy (DMD), you may have heard that the condition is much more common in males than in females. But why is that?

Though rare, DMD is one of the most common inherited neuromuscular diseases. However, because of the way the gene mutation (variation) that causes DMD is inherited, the condition is far less common in girls than boys, according to StatPearls.

Can females get DMD? The answer is yes, but the chances are so slim that few research trials include females in their studies. DMD occurs in 1 out of every 3,500 to 6,000 live male births, compared to 1 in 50 million live female births.

So why are girls less likely to get muscular dystrophy than boys? Read on to learn how DMD is inherited, why it primarily affects males, and what to expect if a female is diagnosed with the condition.

What Is Duchenne Muscular Dystrophy?

Duchenne muscular dystrophy is a rare, genetic disease that affects the skeletal muscles (muscles used for movement) and the heart. Skeletal muscles help you walk, move, and perform everyday tasks.

DMD is caused by a change in the gene responsible for making dystrophin, a protein needed to keep muscles strong. Without enough dystrophin, muscles gradually weaken and break down.

Symptoms of DMD include:

• Scoliosis (abnormal posture or curvature of the spine)
• Behavioral challenges
• Developmental delays
• Difficulty communicating, which can contribute to behavioral challenges
• Learning difficulties
• Problems with mobility and balance
• Muscle weakness

As DMD progresses, it can also lead to breathing difficulties and heart problems. While muscle weakness and damage worsens over time, treatments are available to help slow disease progression and manage symptoms.

How Is DMD Passed Down Through Families?

To know why DMD is more common in males, it’s important to understand a little bit about genetics.

Each person has 23 pairs of chromosomes. These tiny structures carry genes, which are like instruction books that tell your body how to grow, function, and stay healthy. One of these pairs determines biological sex and is made up of two sex chromosomes: X and Y.

• Females typically have two X chromosomes (XX).
• Males typically have an X and Y chromosome (XY).

When a genetic mutation responsible for a specific condition is on the X chromosome, that condition can be passed down from parents to children through what is known as X-linked recessive inheritance.

Duchenne muscular dystrophy is an X-linked recessive inherited condition, meaning it is caused by a mutation in the dystrophin gene located on the X chromosome.

How Does This Genetic Mutation Affect Males and Females Differently?

As males typically have only one X chromosome, they have no backup copy of the dystrophin gene. This means that if the X chromosome they inherit has the mutation that causes DMD, they will develop the condition.

Females, on the other hand, typically have two X chromosomes, so they usually have a working copy of the dystrophin gene that can compensate for the mutated one. Though extremely rare, some females carry the dystrophin gene mutation on both X chromosomes, resulting in DMD.

Females with one mutated X chromosome and one healthy X chromosome are known as DMD carriers. In carriers, the unaffected chromosome serves as a “backup,” helping prevent DMD symptoms.

Anywhere from 2.5 percent to 20 percent of girls who are DMD gene carriers may develop some DMD symptoms that are milder, according to Cleveland Clinic. They are known as manifesting carriers.

What Symptoms Do Female Carriers of DMD Experience?

Most girl carriers experience milder symptoms than boys, according to Cleveland Clinic. This is because females usually have a second, healthy X chromosome that helps protect their muscles from damage.

Delayed Symptoms

Though males with DMD typically begin to show signs of muscle weakness by the age of 3 to 5, females may not notice issues until their teens or even early adulthood.

Milder Muscle Weakness

Because most females with DMD have a second, healthy X chromosome, they often experience milder muscle weakness compared to males. However, as they age, females may still have trouble walking, climbing stairs, and performing other activities that require strong muscles.

Heart and Breathing Issues

Females with DMD face heart and lung complications, similar to males. These problems can develop as the disease progresses. In some cases, females with DMD may experience heart problems like cardiomyopathy (a condition where the heart weakens and cannot pump blood properly). Females can also have sleep apnea (a condition causing breathing to pause or reduce during sleep).

Other Factors That Cause Girls To Experience DMD Symptoms

Although DMD is much more common in males, there are a few rare situations in which a female may develop the condition or experience DMD-like symptoms.

De Novo Mutation

A de novo mutation is a spontaneous genetic change that occurs, rather than being inherited. In rare cases, female carriers may also develop a de novo mutation on their other X chromosome. If both copies of the gene have mutations, they may develop DMD.

X-Inactivation and Skewed X-Inactivation

Typically, females have two X chromosomes, with one X chromosome randomly “turned off” in each cell through a process called X-inactivation. This usually results in about half the cells using the maternal X and half using the paternal X.

In skewed X-inactivation, the X chromosome carrying the dystrophin gene mutation remains active in more cells than usual. This reduces dystrophin production and can lead to DMD symptoms, even though the person has one normal dystrophin gene.

Turner Syndrome

Turner syndrome is a genetic condition in which a female is born with only one X chromosome or with one partially missing X chromosome. Those whose X chromosomes carry the dystrophin gene mutation may develop DMD. However, this is extremely rare, with only a few documented cases.

Find Support for Your Unique Needs

DMD affects each person differently. Some people may experience more severe symptoms, while others may progress slower. If you or a loved one has DMD, work with your healthcare team to manage symptoms. Your care may include:

• Physical therapy to maintain mobility and flexibility
• Heart care to monitor and support cardiac function
• Breathing support to assist with lung function as needed
• Medications to help slow muscle degeneration and improve strength

While DMD is a serious condition, it’s important to remember that people with DMD can live fulfilling lives with the right support. Children with the condition may need help with mobility, but they can often still continue to participate in the activities they enjoy.

Talk With Others Who Understand

On myMDteam, the social network for people with muscular dystrophy and their loved ones, members come together to ask questions, give advice, and share their stories with others who understand life with MD.

Are you a female living with Duchenne muscular dystrophy? What symptoms do you experience? Share your experience in the comments below, or start a conversation by posting on your Activities page.