Causes include:
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001724/
Duchenne muscular dystrophy is caused by a defective gene for dystrophin, it often occurs in people without a known family history of the condition. Boys are affected, while girls are carriers. The sons of females who are carriers of the disease a 50% chance of having the disease. The daughters each have a 50% chance of being carriers.