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The Genetics of DMD

Who can get DMD—how is it inherited?

The gene that causes DMD is located on the X chromosome—and this means that boys are at greater risk of inheriting the disease. This is because boys don’t get a “backup copy” of the gene.

  • Girls inherit two X chromosomes, one from each parent. If a girl’s X chromosome contains a faulty dystrophin gene, they have a “backup” copy of the dystrophin gene, which usually compensates for the faulty one. A girl with the faulty dystrophin gene is called a “carrier”
  • But boys inherit only one of their mother’s X chromosomes along with their father’s Y chromosome. If a boy’s X chromosome contains a faulty dystrophin gene, he will have DMD—he has no “backup” gene

Can girls get DMD?

A girl will only develop DMD if both of her X chromosomes have faulty dystrophin genes. Girls affected by DMD normally have less severe symptoms than boys, but they may need the same treatment and care.

You can see the how the genetics work in this graphic:

A man with DMD can never pass on the condition to his son

This is because an affected father only passes a Y chromosome to his sons, and the DMD-causing gene is located on the X chromosome. However, he will pass the DMD-causing gene onto his daughters because each daughter inherits her father’s X chromosome. These daughters will be carriers.

DMD may affect future pregnancies

If a woman is a DMD carrier, she may have another baby with DMD.

The chances of a carrier having a child with DMD are 1 in 4 (or 25%). This means that for every baby she has, there is a 1 in 4 chance that the child will have DMD.

In all carriers, regular strength check-ups and close heart monitoring are important to make sure that any symptoms that may arise are properly treated. This is why it is so important for female relatives of a boy with DMD to get tested to find out whether or not they are carriers.


*Carriers may show signs and symptoms of DMD and may need treatment. Adapted from the Muscular Dystrophy Association.


Important Terms and Concepts

Basic terms and key definitions

Neuromuscular disorders

Neuromuscular disorders affect the muscles and nerves, and most of the causes are genetic. This means they are either passed down through the family or caused by changes in an individual person’s genes.

Most neuromuscular disorders cause muscle weakness that worsens over time. Signs and symptoms of neuromuscular diseases can vary and may be mild, moderate, or severe.

Most often, when a child has a neuromuscular disease, they don’t grow and develop as fast as other children their age. They are often slow to start lifting their head, sitting, walking, and talking.

Treatment and supportive care may improve the symptoms of a neuromuscular disorder, increasing mobility and even life expectancy.

Muscular dystrophy

Muscular dystrophy is the term for a group of neuromuscular disorders that cause muscle weakness and muscle loss.

Duchenne muscular dystrophy (DMD) is a type of muscular dystrophy that causes muscle weakness that worsens over time. The progression and symptoms can vary from person to person.

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Date of preparation: September 2022