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DILLON, living with Duchenne.

The Role of Genetics in Duchenne

Genetic Mutations

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A Closer Look at Our Body’s Instructions

Amino acids and proteins are the building blocks of life. Our bodies use amino acids to make proteins, which are essential for our bodies to function. Each protein has a specific job – for instance, helping you digest food, helping your hair and nails grow, or helping you fight off infection. To make these important proteins, the body needs instructions so it knows which protein to make and how to make it. These instructions are found in our DNA.

DNA is short for deoxyribonucleic (dee-oxy-rye-bo-new-clay-ick) acid. It is found in nearly every cell in our body and carries all of our genetic information.

A length or section of DNA is called a gene. Each gene is made up of smaller parts called introns and exons. When the body needs to make a protein, instructions in the DNA are given to a similar molecule called RNA, or ribonucleic (rye-bo-new-clay-ick) acid. During this process, the introns are removed and all the exons are linked together to make one long chain of instructions, which are then carried to another part of the cell by messenger RNA (mRNA).

Once there, particles in the cells called ribosomes “read” the instructions and make the correct protein using amino acids.

Genetic Mutations in Duchenne

The mRNA shown below comes from the dystrophin gene and contains 79 exons that are linked together to form the instructions for making dystrophin protein. Researchers have discovered that mutations, or errors, in the dystrophin gene alter the instructions for making dystrophin.

 

Types of mutations include:

  • Large deletions: One or more exons are missing from the dystrophin gene
  • Large duplications: One or more exons have extra copies in the dystrophin gene
  • Other changes: Small changes, such as tiny deletions or changes in a single letter in the instructions

The most common mutation in people with Duchenne is a deletion of one or more exons. Much like a puzzle, these missing pieces prevent the remaining exons from fitting together properly. This causes errors in the instructions for making dystrophin, and the body is not able to produce a working dystrophin protein.

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Inheritance of Duchenne Genetic Mutations

Duchenne is a genetic disorder that can be inherited. While it is possible for someone with no family history to have the disease, it’s most commonly passed down through families. To understand how the disease is inherited, we need to take a closer look at genetics.

Chromosomes are the parts of our cells that carry our DNA. Healthy people normally have 46 chromosomes, divided into 23 pairs. These pairs contain all the instructions our bodies need to make us who we are. We inherit our chromosomes from our parents.

One of these pairs of chromosomes determines if the baby will be a boy or a girl. Girls have 1 X chromosome from their mother and 1 X chromosome from their father, while boys have 1 X from their mother and 1 Y from their father.

 

Duchenne is an X-linked disease, meaning that the genetic mutation that causes the disease is found on the X chromosome.

If a woman has the Duchenne-causing mutation in one of her chromosomes, she is considered a carrier. As a carrier, she likely has no symptoms of the disease, but she has the ability to pass it along to her child. It is not guaranteed that she will pass along the mutation. Typically, there is a 25% chance of having a boy with Duchenne, a 25% chance of having a girl who is a carrier, and a 50% chance of having a baby without the mutation.

Genetic Counseling

Genetic counselors are healthcare professionals who are trained in medical genetics and counseling. They can work with you and other members of your care team to help you:

Understand the genetic cause of Duchenne

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Provide guidance on genetic issues, including family planning
 

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Navigate genetic testing, including understanding the results
 

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Refer you to community or state support services, as appropriate
 

Where can I find a genetic counselor?

You will likely meet with a genetic counselor at a doctor’s office. Specialist clinics such as the Muscular Dystrophy Association (MDA) Clinics and care centers such as the PPMD Certified Duchenne Care Centers also have genetic counselors who can help you.

The Duchenne Registry, a PPMD program, can also help you access genetic testing and genetic counselors. If you or your child needs genetic testing, please contact the Duchenne Registry Coordinators at coordinator@duchenneregistry.org. The Decode Duchenne program also offers free genetic testing for qualified applicants.

The National Society of Genetic Counselors (NSGC) provides a complete array of support services, information, and resources around genetic counseling and genetic testing.

Exon deletion tool

If your child has already had a genetic test and the mutation is an exon deletion, this educational tool can help you prepare for a discussion with your child's doctor or genetic counselor. If you don't know your child's exon deletion, learn more about genetic testing.

Enter your child's exon deletion

Exon
to
Exon

Instructions: Enter the first and last number correlating to your child's deletion in the fields below. If your child has a single deletion, enter the same number in both fields. Example: 12-12, 12-14, 12-75.

This educational tool is designed to provide information about exon deletions only, which is not meant to be used as the basis for diagnosis or deciding upon any course of treatment for Duchenne. This tool does not include point mutations or other small mutations, duplications, multiple deletion ranges (e.g., 14-19 AND 37-50) or creation of a stop codon with potential therapies. Be sure to speak with your child's doctor or genetic counselor about your child's genetic testing results.

Early detection of Duchenne is vitally important.

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