Muscular dystrophy can develop at any age, however the majority of cases are diagnosed in childhood. Young males are more prone than girls to suffer this condition. The kind and intensity of symptoms determine the prognosis for muscular dystrophy. There are four main types of the disease: Duchenne's muscular dystrophy (DMD), limb-girdle muscular dystrophy (LGD), facioscapulohumeral muscular dystrophy (FSHD) and myotonic muscular dystrophy (MMD). People with DMD never walk, even at a very early age. They require constant care because they are vulnerable to developing pneumonia due to poor breathing control, muscle weakness and lack of exercise. Most patients die before their 30th birthday from respiratory failure or cardiac arrhythmia. In LGD, muscle strength is reduced but not enough to cause walking difficulty. People with this type of muscular dystrophy may be able to climb stairs, but cannot support themselves on foot. They usually require a wheelchair for mobility. Life expectancy is normal, but people tend to lose movement in the arms and shoulders as they grow older. FSHD is a rare form of muscular dystrophy characterized by progressive weakening and wasting of muscles of the face, shoulder girdle, chest and upper back.