Researchers have identified a variant of the gene in some patients with amyotrophic lateral sclerosis (ALS). Using human-induced pluripotent stem (iPS) cells, subsequent investigations revealed this variant excessively recruited RNA-binding proteins and disrupted the synaptic formation, which is considered the early impairment in ALS. When excessive binding was blocked, synaptic formation was recovered. These findings describe one of the mechanisms that cause ALS and offer new insights for treatment.