How is Duchenne Muscular Dystrophy inherited?
In Duchenne muscular dystrophy the defective gene is X-linked, meaning that this gene is situated on the X chromosome. Females have two X chromosomes while males have one X chromosome, which they inherit from their mother, and one Y chromosome, which they inherit from their father. In approximately two-thirds of cases the defective gene is passed on to a son through the mother’s faulty X chromosome. In these cases, the mother is known as a ‘carrier ’who, in most cases, will show no symptoms of the disorder. This is because the gene is ‘recessive’, meaning that her normal X chromosome will be predominant and function to produce dystrophin. In only a small minority of carriers there is a mild degree of muscle weakness, usually limited to the shoulders and hips, and these women are known as ‘manifesting carriers’. The genetic fault may have arisen in a previous generation where there may be a known family history. However, in approximately one-third of DMD cases the genetic fault arises i
