Muscular dystrophy (MD) is a genetic (inherited) condition that over time gradually causes the muscles to weaken. This leads to an increasing level of disability.
There are several different types of MD, with different symptoms and patterns of progression. Not all types of MD cause severe disability, but there is currently no cure for the condition.
MD is caused by mutations (cellular changes) in the genes that are responsible for the structure and functioning of a person’s muscles. The mutations can occur spontaneously, but they are normally inherited from a person’s parents.
The mutations cause changes in the muscle fibres, which interferes with the muscle’s ability to function. Over time, this causes increasing disability.
Types of muscular dystrophy
There are over 30 types of MD, each with slightly different symptoms. They can appear at different ages, affect different muscles, and progress at different rates. Some of the more common types of MD are listed below.
Duchenne muscular dystrophy
Duchenne MD is the most common and most severe form of MD. It usually affects boys and is diagnosed at around three years of age. It starts in the leg muscles before quickly progressing to other muscles groups.
Becker muscular dystrophy
Becker MD is closely related to Duchenne MD, but it is milder and less common. Like Duchenne MD, Becker MD tends to affect boys, although it is not usually diagnosed until around 10 years of age. It also progresses slower.
Myotonic muscular dystrophy
Myotonic MD is the most common form of MD in adults, although it can appear at any age. Both sexes can develop myotonic MD, which affects the smaller muscles, such as those in the face, jaw, neck, and hands.
Limb-girdle muscular dystrophy
Limb-girdle MD has around 15 different varieties. It can affect both sexes and usually appears in early adulthood. Limb-girdle MD initially starts in the muscles around the hip girdle and the shoulder girdle, but it can also progress quite quickly to other areas.
Facioscapulohumeral muscular dystrophy
Facioscapulohumeral MD affects the muscles in the face (facio), shoulders (scapula), and upper arm (humeral). This can affect both sexes, with symptoms starting between 10-40 years of age and progressing slowly.
Oculopharyngeal muscular dystrophy
Oculopharyngeal MD affects the muscles of the eye (ocular) and throat (pharyngeal). The condition affects both sexes, usually from between 50-60 years of age.
How common is muscular dystrophy?
Duchenne MD is the most common type of MD. Worldwide, it affects one boy who is born in every 3,500 . The second most common type is myotonic MD, which affects around one person in every 8,000 worldwide.
Other types of MD are less common - for example, facioscapulohumeral MD affects approximately one person in every 20,000 in Britain. As most cases are inherited, whether or not someone is likely to have MD will depend on whether any of their close relatives have ever had the condition.
Outlook
MD is a progressive condition, which means that it gets worse rather than better. It can start with one group of muscles and then move onto others. If MD begins to affect the cardiac (heart) muscles, or the respiratory system (breathing) muscles, it then becomes life-threatening.
The progression of MD varies, not only between the different types, but within them as well. Some genetic mutations can cause a milder version of the condition, and some will be more severe.
Children with Duchenne MD may be in a wheelchair by the age of 10, and the condition can be life-threatening by the age of 30. Those with Becker MD may need a wheelchair by the time that they are 40 or 50 years of age, but they should be able to live a normal lifespan.
Treatment can help with the physical disabilities and cardiac problems, but cannot cure the condition. New research is looking into ways of repairing the genetic mutations and damaged muscles, but it is still in the early stages.
