C9orf72 and amyotrophic lateral sclerosis: PolyP, a ubiquitousand negatively charged biopolymer, is enriched and excessively releasedby both mouse and human iPSC-derived astrocytes harboring pathogenicmutations in SOD1, TARDBP, and C9ORF72., Through gain-and loss-of-function experiments, it was also demonstrated that thisaberrant release of polyP from ALS and ALS/FTD astrocytes is neurotoxic,promoting MN death by inducing neuronal hyperexcitability and consequentCa2+ overload.,