While in graduate school, at age 21, Dr. Hawking was diagnosed with Amyotrophic Lateral Sclerosis (ALS), commonly referred to in the U.S. as Lou Gehrig’s disease. As ALS progresses, the degeneration of motor neurons in the brain interfere with messages to muscles in the body. Eventually, muscles atrophy and voluntary control of muscles is lost. People with ALS typically maintain intelligence, memory, and personality, even in the late stages of the disease.

Source: Access Computing