Duchenne muscular dystrophy is an inherited disorder that affects children on their mother’s side via the X chromosome in a recessive pattern.
A recessive pattern means the effect of the inherited disorder is only seen if both genes carry the mutation. Below, we look at how this gene is passed on and the likelihood that the mutation will result in a child being diagnosed with Duchenne.
We want to make it clear that no one is to blame for their child’s illness.
Many families have no prior history of the disorder and receiving this diagnosis is a complete shock. We understand how difficult it is to realize your child is coping with a genetic condition, and we urge you to know you are not alone and you are not at fault.
How does a female carrier pass on the Duchenne mutation?
- All humans have two sex chromosomes: the X and the Y chromosome.
- Males have only one X and one Y chromosome, while females have two copies of the X chromosome.
- The recessive nature of the DMD gene means you need two mutations in the X chromosome to have an effect. Because females have two copies of the X chromosome, only one of these copies are affected and the second copy is protected against the inherited disorder. This is why, females are carriers and do not have Duchenne.
- Males only have one X chromosome, which they get from their mother, so if that X chromosome has the DMD mutation, the male will have Duchenne muscular dystrophy because there is no second gene on their Y chromosome to protect them.
- A woman who carries the DMD gene has a 50% (or 1 in 2) chance of passing it on to their son, resulting in Duchenne. Each time a carrier mother has a daughter, there is a 50% (or 1 in 2) chance her daughter will become a carrier.
You may have also heard the term “manifesting carriers.” These are female Duchenne carriers who can experience symptoms such as muscle weakness and heart problems. If you are a carrier, it is vital to see a health care professional familiar with Duchenne and undergo cardiac evaluation and follow-up. While approximately 70% of cases are caused by an inherited mutation, 30% of cases result from a de novo mutation or spontaneous mutation.
Some mothers test negative for carrier status but can carry the Duchenne mutation in their egg cells. This is called germline mosaicism. Germline refers to a woman’s egg cells and mosaicism means some cells have a different genetic make-up than others. In the case of Duchenne, some of the mother’s egg cells can contain a mutation in the DMD gene, and she could theoretically have more than one child with Duchenne, despite not being a carrier.
It is important that after their child is diagnosed, mothers get tested and speaks to a genetic councillor about future family planning. It is also important that all female relatives of a boy with a confirmed diagnosis of Duchenne are tested. This insight into the broader picture of your genetics will help each of your family members make the best possible choices for them and their children, now and in the future.
Click the button below to learn more about the causes of Duchenne.
Click the button below to learn more about the genetics of Duchenne.