Amyotrophic lateral sclerosis (ALS), also known as motor neurone disease (MND) or Lou Gehrig's disease, is a disease that causes the death of neurons controlling voluntary muscles. Some also use the term motor neuron disease for a group of conditions of which ALS is the most common.Amyotrophic lateral sclerosis (ALS), also known as motor neurone disease (MND) or Lou Gehrig's disease, is a disease that causes the death of neurons controlling voluntary muscles. Some also use the term motor neuron disease for a group of conditions of which ALS is the most common.A nervous system disease that weakens muscles and impacts physical function.In this disease, nerve cells break down, which reduces functionality in the muscles that they supply. The cause is unknown.The main symptom is muscle weakness.Medication and therapy can slow ALS and reduce discomfort, but there's no cure.