The major characteristic of Duchenne Muscular Dystrophy is the progressive weakness of all muscles; proximal muscles of the limbs are most severely affected. Difficulties in rising from the floor, running and going upstairs are usually evident in the first 2-3 years of life. Enlarged calves can be seen in most children, especially in the early phases of the disease. The weakness is progressive and children with the Duchenne Muscular Dystrophy will lose the ability to walk by the age of 13 (the average age being approximately 9). This is due to a combination of weakness and contractures affecting the ankles, knees and hips. A frequently-associated feature (30% of cases) is mild learning disability. Presentation with predominantly cognitive problems is not uncommon (such as speech delay). This is not progressive.