Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Bethlem myopathy ?
    ### Response:
    Bethlem myopathy is an inherited movement disorder characterized by progressive muscle weakness and joint stiffness (contractures) in the fingers, wrists, elbows, and ankles. Due to a progressive course, up to two-thirds of people with this condition require a walker or wheelchair after the age of 50.
    