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.