By 2040, experts estimate that nearly 400,000 people worldwide will be living with amyotrophic lateral sclerosis (ALS), commonly known as Lou Gehrig's disease. This degenerative nervous system disease damages nerve cells responsible for controlling voluntary muscle movement, leading to progressive muscle weakness, loss of muscle mass and, eventually, difficulty breathing. Current ALS diagnosis relies on neurological evaluations and the presence of symptoms; at present, there is no definitive diagnostic test.