“ In just over half of all cases the mother carries the gene but is usually not herself affected by it. Such women are known as ‘carriers’. Each subsequent son of a carrier has a 50:50 chance of being affected and each daughter has a 50:50 chance of being a carrier herself. A small number of female carriers of the gene have a mild degree of muscle weakness themselves and are then known as ‘manifesting carriers’.”
A Manifesting Carrier is a female “carrier of Duchenne or Becker Muscular Dystrophy (DMD or BMD) genetic mutation and displays symptoms of that
muscle disorder. The severity can vary from mild generalised weakness to an inability to walk, differing from individual to individual. Only females can become Manifesting Carriers and onset of symptoms usually occurs between 16 to 48 years of age. It affects approximately 5-
10% of all female carriers of DMD or BMD.
Below is a link to an online publication that covers Becker as well
From The Muscular dystrophy campaign
Only females can become Manifesting Carriers and onset of symptoms usually occurs between 16 to 48 years of age. It affects approximately 5-
10% of all female carriers of DMD or BMD. DMD and BMD are both X-linked recessive disorders, and Manifesting carriers arise in a few of the female carriers. One third of DMD and BMD cases are spontaneous, so it is possible to be a Manifesting Carrier without a family history.
What symptoms does a manifesting carrier have?
There are as wide a variety of presentations of manifesting carriers as there are of males with
DMD and BMD. …. Some women may only have very mild problems with muscle weakness late in adult life.
Some women get aches and pains in their muscles as their first complaint and may notice enlargement of their calves and other muscles.
There are other manifestations of Duchenne muscular dystrophy, for example involvement of intellectual function and of heart muscle. Problems in these areas can be the only signs that someone is a manifesting carrier. These presentations are less common than a woman noticing
a mild but progressive weakness involving usually first her legs but later on the arms as well.
Most manifesting carriers notice some progression of their muscle problem with time; however it is rare for there to be any sudden deterioration.