Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease and Charcot disease, is a specific disorder that involves the death of neurons. In a number of countries the term motor neurone disease (MND) is commonly used, while others use that term for a group of five conditions of which ALS is the most common. ALS is characterized by stiff muscles, muscle twitching, and gradually worsening weakness due to muscles decreasing in size. This results in difficulty speaking, swallowing, and eventually breathing.