Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) amyotrophic lateral sclerosis ?
    ### Response:
    Amyotrophic lateral sclerosis (ALS) is a progressive disease that affects motor neurons, which are specialized nerve cells that control muscle movement. These nerve cells are found in the spinal cord and the brain. In ALS, motor neurons die (atrophy) over time, leading to muscle weakness, a loss of muscle mass, and an inability to control movement.
    