Genetic testing as part of diagnosis or to explore variant-specific therapies is now common for boys with Duchenne muscular dystrophy (DMD) — but should their parents get genetic testing, too? Read more to understand the genetics of DMD and how genetic testing may be beneficial.
The basics of DMD genetics
To understand why genetic testing in DMD may be useful, it is helpful to know how DMD is inherited.
The DMD gene is located on the X chromosome. A mother with a DMD mutation on one of her two X chromosomes has a 50% chance of passing the mutation on to her son: He may inherit the chromosome carrying the mutation, but he’s equally likely to inherit the healthy chromosome.
Roughly 70% of boys with DMD inherited the DMD gene mutation from their mother in this way. In the other third of cases, the mutation develops spontaneously, which means the mutation is new and not inherited from a parent.
Daughters also have a 50% chance of inheriting their mother’s mutated DMD gene — but because girls have two X chromosomes, her healthy X chromosome will (usually) protect her from developing Duchenne symptoms. She will, however, be a carrier of the mutation, and have a 50% chance of passing it on to her children.
Read more about DMD testing and diagnosis
What genetic testing can tell you
If your child has been diagnosed with Duchenne, a genetic counselor can work with you to understand what genetic testing the rest of your family may need, and the best next steps. In general, however, after a boy is diagnosed with DMD it’s generally recommended his mother get genetic testing to learn if she is a mutation carrier. This is important for understanding other family members’ risk for developing DMD, and for her own health as well.
If a mother is a genetic carrier, her other children should be tested to learn if they carry a mutated DMD gene. This can help other sons who are found to have DMD start treatment earlier on. Other members of her family, such as sisters and female cousins, may also want to get genetic testing to learn if they are carriers.
Though most women who carry DMD gene mutations don’t experience any symptoms, around 2.5% to 20% will, namely muscular symptoms and heart problems. Some research suggests women carriers should consider regular cardiac evaluations to help protect their health.
Knowing carrier status is also important in family planning. If parents want to grow their family, a genetic counselor and an OB/GYN can help them understand their chances of having another child with DMD and their reproductive options, such as in-vitro fertilization.
If you are facing these decisions, remember that genetic counselors are here to help provide fact-based advice for your family’s specific case. Genetic testing can sound like a scary thing to go through, but your doctor will be able to provide clarity with regards to how genetic testing is carried out, the wider implications of the results and the help and support that is available.
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