We found that RGMa with its C-terminal domain (variant C) was increased in the CSF of patients with ALS than in those with ONDs, such as MS and PD, and in NDs such as normal pressure hydrocephalus and muscle disease, raising the possibility that the RGMa/NEO1 axis is more essentially involved in the pathogenesis of ALS than in other diseases. Here, NEO1 is linked to amyotrophic lateral sclerosis.