Condition in which muscular fibre gradually degenerates; the muscles weaken, and deposits of fat can cause them to swell. There are various forms of muscular dystrophy, all of which are hereditary and have no known treatment. There are three principal categories. In the pseudo-hypertrophic form (Duchenne type) calf and underarm muscles are enlarged, and there is weakness in upper and lower limb muscles; the disease begins before the age of three, and affects mainly boys. Patients have difficulty with walking and climbing steps. The disease causes a high degree of invalidity. The limb-girdle variety begins between the ages of 10 and 30, and is equally common in men and women. Muscles are seldom enlarged, but this form too causes severe invalidity in the course of years. The third group is the facioscapulohumeral variety (Landouzy-Dejerine type); it can begin at any age. Eyelids droop, and the upper lip may also protrude; later shoulder muscles are affected, and possibly limb-girdle muscles. This variety of the disease develops slowly, and most patients can lead a normal life.