Provided are a diagnosis marker, a diagnosis method, and a therapeutic agent suitable for diagnosing and treating amyotrophic lateral sclerosis (ALS). Also provided are an animal model and a cell model suitable for developing a therapeutic agent and a treatment method for ALS. The diagnosis method for ALS includes: an isolation step in which a nucleic acid is isolated from a specimen taken from a subject； a detection step in which bases expressed in a human chromosome 10 optineurin (OPTN) gene region are detected from the isolated nucleic acid； and a determination step in which it is determined whether or not the detected bases are mutated.
