Problems are usually not evident until 18 months to 4 years of age . Although with increasing awareness of the problem , Some boys are diagnosed earlier . At least half of affected boys do not walk until 18 months of age or later . In retrospect , Almost all parents have noted that their child never walked or ran normally . Over the first few years of life these children have difficulty climbing and getting up from the floor.
Parents often comment that their child falls frequently .
Walking up on the toes is common . The boys are not able to keep up with their friends in physical activities at kindergarten or school and they are often regarded as clumsy or lazy . Some parents notice that their son has large calf muscles . This enlargement is due mainly to an increase in fatty tissue in the muscle . This enlargement is a sign of muscle disease rather than a indication of good strength .