How is Duchenne inherited?
In around two thirds of cases of Duchenne the faulty dystrophin gene is passed down through the family. The gene that is affected in Duchenne – the dystrophin gene – is located on the X chromosome. This is one of the chromosomes that determines our gender.
Males have one X chromosome inherited from their mother and one Y chromosome inherited from their father. If their X chromosome contains a faulty dystrophin gene, they will have Duchenne muscular dystrophy (see diagram right).
Females on the other hand, have two X chromosomes, one inherited from each parent. If one X chromosome contains a faulty dystrophin gene the healthy dystrophin gene on the other X chromosome can compensate for it and therefore females usually don’t show any symptoms or symptoms are very mild. These girls are known as carriers and could potentially pass the condition on to their sons.
If a male with Duchenne were to have children with a non-carrier female, their sons would not inherit the condition and their daughters would all be carriers.
It is important to remember that Duchenne is nobody’s fault and nobody did anything wrong to cause it. An appointment with a genetic counsellor can help with understanding the inheritance of Duchenne.
NOTE: the likelihood of the four outcomes in the diagram is equal, so in each pregnancy there is a one in four chance of having a boy with Duchenne.