Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Duchenne and Becker muscular dystrophy ?
    ### Response:
    Muscular dystrophies are a group of genetic conditions characterized by progressive muscle weakness and wasting (atrophy). The Duchenne and Becker types of muscular dystrophy are two related conditions that primarily affect skeletal muscles, which are used for movement, and heart (cardiac) muscle.
    