A look into Duchenne muscular dystrophy

(BPT) – Hearing a health provider say “It’s a boy!” during an ultrasound can be one of the most exciting moments on the pregnancy journey for expecting parents, eagerly anticipating the birth of a healthy child. It’s a journey that will be filled with many exhilarating milestones, but for some expectant parents, it may include having to consider the child’s risk of having a genetic disease that affects primarily males, such as Duchenne muscular dystrophy.

Although Duchenne is considered the most common fatal inherited disorder affecting boys that is diagnosed in childhood, any parents know little or nothing about this disease. A progressive form of muscular dystrophy, Duchenne occurs primarily in boys and is caused by an alteration (mutation) in the gene that produces a protein called “dystrophin.” Duchenne is an X-linked condition; this is why males are predominately affected.

While many women are asymptomatic carriers, some also have health effects. Duchenne frequently occurs in people who have no known family history of the disease. Although symptoms may start earlier, the average age at which boys are diagnosed is 4 to 6, when families may already have planned, or are planning, more children. For this reason, parents are often unaware that they may be at high risk of having another child who could inherit this genetic disorder.

Duchenne muscular dystrophy has a similar incidence rate as Cystic fibrosis and is more common than Cystic fibrosis in certain ethnic groups. Unlike Cystic fibrosis, however, Duchenne is not a widely screened-for condition, which leaves many families unaware that they might be at-risk for passing this changed gene to their children.

Fortunately, expectant parents can now easily find out if they are carriers of hundreds of genetic disorders — including Duchenne muscular dystrophy — through a simple blood or saliva test. Even before a couple becomes pregnant, new screening tests, including Natera’s Horizon Carrier Screening, can help determine if one or both parents carry a changed gene for up to 274 genetic conditions, with results generally provided within 14 days. The Horizon test is also the only genetic carrier-screen that offers testing for Duchenne on all panels and detects more than 90 percent of inherited Duchenne gene mutations.

“Like most women, I had no idea I was a carrier for Duchenne until my sons were diagnosed on the same day at ages 4 and 6,” said Pat Furlong, a founding president and CEO of Parent Project Muscular Dystrophy, a non-profit organization dedicated to ending Duchenne. “It’s encouraging to know that moms who are considering a pregnancy can now take a simple test to learn about their risks for Duchenne and other genetic diseases.”

Some important facts about Duchenne include:

How common is Duchenne muscular dystrophy?

Duchenne muscular dystrophy occurs in about one in every 3,500 male births, which is about the same incidence as Cystic fibrosis.

What happens when the Duchenne muscular dystrophy gene is altered?

The Duchenne gene codes for a protein called dystrophin, which is crucial for muscles to work properly. Without dystrophin, muscle fibers degenerate and are gradually replaced by fat and connective tissue until voluntary movement becomes impossible.

Duchenne muscular dystrophy is also associated with a heart condition called cardiomyopathy, in which cardiac muscle is weakened by a lack of dystrophin, preventing the heart from pumping blood efficiently. Heart failure due to Duchenne cardiomyopathy typically begins in adolescence, progressively worsens, and results in death (often before age 30).

What are the symptoms of Duchenne?

The most common symptoms are delayed motor skills (boys may sit, stand or walk at a later age than other children) and may also experience a delay in learning language skills. Muscle weakness typically begins in early childhood and worsens over time, usually resulting in wheelchair dependence by adolescence.

Is it true that only mothers can pass on the mutated Duchenne gene?

Yes. Duchenne is an X-linked condition, and a characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons. Approximately two-thirds of males with Duchenne have inherited the disease from their mothers; the other one-third have a mutation, or change, in the dystrophin gene that is a new change in them, and was not inherited.

If a woman is a Duchenne carrier, what is the likelihood of her child/children being affected?

There is a 50 percent chance her next child would either have Duchenne if it’s a boy, or be a Duchenne carrier if it’s a girl.

Do female carriers have symptoms?

Although many carriers are asymptomatic, the majority do not experience the same disease severity as boys with Duchenne, some may experience symptoms such as some degree of muscle weakness or cardiomyopathy.

Why should I be tested for Duchenne muscular dystrophy?

Genetic-carrier screening gives women and their partner’s valuable information to help them make the reproductive choices that are right for them and their families. Genetic screening can also help ensure earlier intervention at birth, which can improve the overall quality of life of a child with Duchenne. A woman who is a carrier for Duchenne should have regular checkups with a heart specialist, particularly if she is pregnant or planning a pregnancy.

What are my options if I am a carrier?

If you are at risk of passing on Duchenne or any genetic disease, you could consider:

* natural pregnancy — with or without prenatal diagnosis

* pre-implantation genetic diagnosis (PGD) with in vitro fertilization (IVF), which allows for the testing and transferring of embryos that are free of disease

* adoption

* use of an unrelated egg donor

For more information on pre-pregnancy and prenatal genetic tests, please go to natera.com/dmd.

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