Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Myofibrillar myopathy ?
    ### Response:
    Myofibrillar myopathies (MFM) are a group of neuromuscular disorders characterized by slowly progressive weakness that can involve both proximal muscles (such as hips and shoulders) and distal muscles (those farther away from the trunk). Some affected individuals also experience sensory symptoms, muscle stiffness, aching, or cramps.
    