Boys are born with one X-chromosome from their mother and one Y-chromosome from their father. Since boys have only one X-chromosome, if the X-chromosome they receive from their mother has a gene mutation that causes Duchenne, the boy will be born with Duchenne.
Girls are born with two X-chromosomes, one from their mother, and one from their father. If a girl has one X-chromosome with a gene mutation for Duchenne, her body will generally choose to activate the normal X-chromosome. When this occurs, the girl becomes a carrier, meaning that she can pass Duchenne on to her sons, and that her daughters can also be carriers. She many develop a few, if any, symptoms of Duchenne.
If the girl’s body chooses to activate the X-chromosome with the mutation for Duchenne, the girl will have symptoms of Duchenne and be a carrier. She will then be a manifesting carrier of Duchenne.
What does it mean to be a ‘carrier’ of Duchenne muscular dystrophy?
A woman who is a carrier of Duchenne muscular dystrophy has one X-chromosome with the altered dystrophin gene and one normal X-chromosome. Some women who are carriers experience increasing muscle weakness and fatigue, known as carrier symptoms. All women who are carriers should have their heart checked regularly as the heart muscle can be affected.
What if I want to have more children?
Women with a family history of Duchenne are encouraged to seek genetic counselling to understand the risks and options before getting pregnant. Once you are pregnant, testing may be available to determine if your unborn child has inherited Duchenne.