Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Duchenne muscular dystrophy ?
    ### Response:
    Duchenne muscular dystrophy (DMD) is a rapidly progressive form of muscular dystrophy that occurs primarily in boys. It is caused by a mutation in a gene, called the DMD gene, which encodes the muscle protein dystrophin. Boys with Duchenne muscular dystrophy do not make the dystrophin protein in their muscles.
    