What are female (or manifesting) carriers? If a mother of a child with DMD has a mutation in her DNA that she passes to her child, she is called a “manifesting carrier.” These girls and women are called manifesting carriers because they produce reduced amounts of dystrophin. Some female carriers of a faulty dystrophin gene have very mild symptoms of DMD, including fatigue, mild muscle weakness and cramping. A female who is a carrier has an increased risk of developing cardiac and skeletal muscle weakness and dysfunction. Female carriers of DMD need to have their hearts checked every 3 to 5 years (ECG, cMRI or echo) if their hearts are normal (more often if recommended), as they can also have the same type of heart problems as people living with Duchenne. Knowing carrier status helps to identify this risk in order to get appropriate advice and treatment. We recommend speaking with your doctors and a genetic counsellor to explain all this in detail. Germline Mosaicism: A small number of women who do not test positive as carriers for Duchenne may still be able to pass a faulty DMD gene to their children. This situation is called germline mosaicism and is caused by a mutation in the DMD gene in the cells of some of the mother’s eggs. The mutation is not seen in the DMD gene in the rest of the mother’s cells. If one of the affected eggs is fertilized, the resulting child will have DMD if a boy or be a female carrier if a girl. It is estimated that around 15% of mothers of boys with Duchenne, who do not appear to be carriers, could pass a faulty DMD gene to their children in this way.