Like other muscular dystrophies it is a wasting disease of muscle. It usually begins in childhood or adolescence. The features, which make it unique and different from other muscular dystrophies, are the early development of muscle contractures, the distribution of muscle weakness, and the fact that the heart may be affected in a particular way.
What are muscle contractures?
This is a tightening and shortening of certain muscle groups so that the joints, which are involved, become increasingly difficult to move. Such contractures are common at a late stage in most muscle wasting diseases and result from inactivity. But in this disease muscle contractures develop very early or before there is any marked muscle weakness.
What effect do contractures have?
In this condition they limit elbow straightening so that the arms are often held in a semi-flexed way, they result in a tendency to walk on the toes, and they limit forward bending of the neck.