Becker muscular dystrophy is a disabling condition but milder than Duchenne; it develops in young adults.
Becker muscular dystrophy (MD) is very similar to Duchenne MD except it progresses much more slowly and affects primarily the legs and pelvis. It might also spread to the arms and neck, although its effects will not be as prominent as they are in the lower body.
Becker MD is an X-linked recessive disease that affects approximately three out of every 100,000 boys. Its onset usually occurs between the ages of 7 and 26.
Cause of Becker muscular dystrophy
Becker muscular dystrophy is also due to a mutation and abnormalities in dystrophin. A fault in a particular gene (dystrophin) carried on the X chromosome leads to the formation of a faulty protein in muscle fibres. This protein, also called dystrophin, is absent or severely abnormal in Duchenne muscular dystrophy.
In Becker muscular dystrophy a milder fault makes the dystrophin molecule smaller (or occasionally larger) or less abundant than normal. When dystrophin is abnormal the muscle fibres gradually break down and the muscles slowly become weaker. These dystrophin abnormalities in muscle provide a very good test for the diagnosis of Becker muscular dystrophy.
Symptoms of Becker muscular dystrophy
It is characterized by weakening and greater enlargement of calves during adolescence or young adulthood, but later onset and slower rate of progression.
Frequently associated with colour blindness. Cardiac involvement is absent and the life span is often normal, as distinct from the Duchenne form of muscular atrophy.
Onset in the second and third decades of life. Etiology unknown. Inheritance is recessive X-chromosomal. The mutated gene is the same as in Duchenne's muscular dystrophy, but the mutation is different.