Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the symptoms of Bethlem myopathy ?
    ### Response:
    What are the signs and symptoms of Bethlem myopathy? Bethlem myopathy mainly affects skeletal muscles, the muscles used for movement. People with this condition experience progressive muscle weakness and develop joint stiffness (contractures) in their fingers, wrists, elbows, and ankles.
    