ALS causes a slow weakening of the motor neurons, and then death. Motor nerves spread through the entire body from the brain to the spinal cord to muscles. They stop sending signals to the muscles when motor neurons are impaired, so that the muscles can't function. In 5% to 10% of citizens ALS is hereditary. ALS is the most common degenerative disease of motor neuron system. While ALS is incurable and fatal, care may prolong the duration and positive quality of life for patients, with median survival of 3 years. Drugs and therapy can slow down ALS and minimize pain, but there is no cure.