Female carriers

Finding out you're a carrier

DMD and BMD are caused by a mutation (change) in a gene. To confirm this mutation, you need a DNA-based genetic testing. The gene is located on the X-chromosome and is inherited in a recessive manner. This means that in general only boys can have the disease. Females can, however, be carriers, who can pass on the disease to their sons, and the mutated gene to their daughters. In most cases female carriers do not experience any disease symptoms. In most cases, mothers find out they are a carrier once their son is diagnosed with Duchenne or Becker muscular dystrophy.

In one third of the cases, a mutation is not inherited, but happens spontaneously. In that case the patient is often the first DMD/BMD patient in the family and chances are really small that other female members are DMD/BMD carriers.

The risks of being a carrier

If you are a carrier, it is a good idea to inform other women in your family. Female family members (daughters, sisters, aunts, nieces) may also be a carrier. A genetic counselor can let you know which family members are at risk of being carriers. It is advised to talk with your family since:

Carriers have with each pregnancy a chance of 1 out of 4 (25%) to have a son affected with DMD/BMD. So if a family member is planning to have children, it is important for her to investigate if she is a carrier.
If this is indeed the case, there may be options to prevent having a son affected with DMD/BMD. You can discuss this with a genetic counselor or clinician.
Although this is usually only at a later age, a minority of female carriers experience some degree of muscle weakness or, more often, heart problems. It is therefore important that they are regularly seen by a cardiologist.
It sometimes takes a while before the diagnosis DMD/BMD is made. If you know that DMD/BMD carriership exists in your family, this may help finding the cause of your son’s health complaints.

Explaining you're a carrier

What to tell your family about the heritability of DMD/BMD and how you can tell this, depends on what suits you best. If they consider genetic testing or have additional questions, they could ask their general practitioner to refer them to a clinical geneticist.

Sharing this news might make them feel uncomfortable or uncertain. You can try comforting them, and direct them to a clinician or genetic counselor for support. Remember it’s not your job to convince your family members to have genetic testing. This is their own decision.