A Study to Assess FLX-787 in Subjects With Motor Neuron Disease Experiencing Muscle Cramps.

The COMMEND Study will assess the safety and effectiveness of FLX-787 in men and women with Motor Neuron Disease \[including Amyotrophic Lateral Sclerosis (ALS), Primary Lateral Sclerosis (PLS) or Progressive Muscular Atrophy (PMA)\] experiencing muscle cramps. Participants will be asked to take two study products during the course of the study. One of these study products will be a placebo. Approximately 120 participants in approximately 30 study centers across the United States are expected to take part. Participants will be in the study for approximately 3 months and visit the study clinic 3 times.