Genetic Counseling Spotlight: Duchenne Muscular Dystrophy

There are many genetic conditions that can be inherited from a parent to a child. There are also genetic conditions that can happen randomly, caused by a mistake in a person’s genetic instructions that happened before that person was even born. Almost all genetic conditions can occur in both ways, randomly, and inherited from a parent. Duchenne Muscular Dystrophy is a complex genetic condition that can be inherited from a female and also happen new or randomly in a person.

Duchenne Muscular Dystrophy (DMD) primarily affects males but can sometimes affect females as well. DMD is caused by a genetic mutation, or change in a segment of our genetic instructions, called the DMD gene. When the DMD gene does not work properly, the body does not produce enough of the protein dystrophin, which our muscles need in order to function. The muscles in the body progressively become weak and damaged until eventually a person does not have control over their muscles. Children will progressively have trouble walking, breathing, and eventually the muscles in their heart will stop working.

DMD occurs in 1 in 3,500 to 5,000 male births in the world. It is inherited in an X-linked pattern, which means females are carriers (carry the gene mutation on one of two X chromosomes) and males are affected (inherit the gene mutation on their only X chromosome). Females do not typically have symptoms. Males are often diagnosed around the age of 5. Children can experience a variety of symptoms, including not walking until approximately 18 months of age, falling down often, larger calves than other children, fatigue, walking on toes with legs apart or their belly pointed out, delayed speech, or needing help getting up from the floor. Approximately 90% of people with DMD are in a wheelchair by the age of 15 years old.

Females can have similar or milder symptoms than males due to alternative genetic mistakes. In addition, females can have symptoms of DMD due to X-chromosome inactivation. Females have two X chromosomes in every cell of their body. One X is actually turned off and does not provide genetic instructions needed for our body. If a female has one X with the DMD gene mutation and one X that is normal, and enough of her cells turn off the normal X randomly instead of the X with the DMD gene mutation, she can have symptoms of DMD.

There are more than 30 forms of muscular dystrophies, including DMD. A milder form of DMD, based on the location of the gene mutation in the DMD gene is called Becker muscular dystrophy. Becker muscular dystrophy (BMD) presents with progressive muscle weakness, but slower progression than DMD. Individuals with BMD can remain ambulatory into their 30s.

If you or a family member are affected by DMD and you would like to know your risks of being a carrier and passing on the DMD gene mutation to a child, you can meet with a genetic counselor to discuss your risks. A genetic counselor will draw a pedigree, or family tree, and ask if anyone in your family has symptoms of DMD, been genetically tested for DMD, or has any additional health concerns. You can discuss with your genetic counselor the option of pursuing genetic testing to determine if you are a carrier of DMD. In some cases, a person with DMD may not have a family history of DMD because the mutation is new in them, which means family members are not at increased risk to have a child affected by DMD.

Please contact AT-GC to meet with a genetic counselor to discuss your risks.

Resources:
https://www.ncbi.nlm.nih.gov/books/NBK1119/
https://www.duchenne.com/about-duchenne
https://rarediseases.info.nih.gov/diseases/6291/duchenne-muscular-dystrophy

Image:
https://treat-nmd.org/treat-nmd-diseases/duchenne-muscular-dystrophy/

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