Astrocytes carrying ALS-causing mutations, such as SOD1, fused in sarcoma (FUS), or C9orf72, would exhibit profound in vitro toxicity towards co-cultured motor neurons, impairing their neurite outgrowth, synaptic integrity, and overall survival [154,155,156,157,158]. The gene discussed is FUS; the disease is amyotrophic lateral sclerosis.