This is one of more than 20 types of muscular dystrophy. All the muscular dystrophies are caused by faults in genes (the units of inheritance that parents pass on to their children) and they cause progressive muscle weakness because muscle cells break down and are gradually lost. The Duchenne type affects only boys (with extremely rare exceptions). This is a very serious condition. Most affected boys develop the first signs of difficulty in walking at the age of 1 to 3 years and are usually unable to run or jump like their peers, they often struggle to climb stairs and need to use a banister for support. Rising from the floor can also prove difficult.
As the condition progresses boys with DMD are unable to walk as far or as fast as other children and may occasionally fall down. Some boys also have learning and or behavioral difficulties, which may begin to manifest at this stage. By about 8 to 11 years (rarely earlier or a little later) boys become unable to walk and by their late teens or twenties the condition is severe enough to shorten life expectancy.