ALS is a progressive, fatal, neurodegenerative disease caused by the degeneration of motor neurons, the nerve cells in the central nervous system that control voluntary muscle movement. The disorder causes muscle weakness and atrophy throughout the body as both the upper and lower motor neurons degenerate and die, ceasing to send messages to muscles. Unable to function, the muscles gradually weaken, atrophy, and develop fasciculations (twitches) because of denervation. Eventually, the brain completely loses its ability to initiate and control voluntary movement. The disease does not necessarily debilitate the patient's mental functioning in the same manner as Alzheimer's disease or other neurological conditions. Rather, those suffering advanced stages of the disease may retain the same memories, personality, and intelligence they had before its onset. My uncle Steve means the world to me :)