In Duchenne muscular dystrophy, the mutation occurs in a gene called dystrophin, which is located on the X chromosome or sex-chromosome (girls have two X chromosomes and boys have only one). In just over half of cases, the condition is inherited from the mother who is a ‘carrier’, but it can also be caused by a new mutation in the child’s genes.
If a woman carries the mutation, then she is known as a ‘carrier’. Usually female carriers are not affected because they have a second X chromosome, from which the dystrophin protein can be produced. A small number of female carriers have a degree of muscle weakness themselves, and they are known as ‘manifesting carriers’.
Each son of a carrier has a 50:50 chance of being affected, and each daughter has a 50:50 chance of being a carrier.
Genetic advice (counselling), and testing for other family members at risk of being carriers, should be provided as soon as possible following the diagnosis of a boy with Duchenne muscular dystrophy. Your clinician or GP can arrange this for you.