Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) myotonic dystrophy ?
    ### Response:
    Myotonic dystrophy is part of a group of inherited disorders called muscular dystrophies. It is the most common form of muscular dystrophy that begins in adulthood.  Myotonic dystrophy is characterized by progressive muscle wasting and weakness. People with this disorder often have prolonged muscle contractions (myotonia) and are not able to relax certain muscles after use.
    