C9orf72 and amyotrophic lateral sclerosis: To understand the cell-autonomous consequence of the C9orf72 mutation on human MG, we first generated monocultures of hiPSC-MG, using established protocols (23, 24), from three pairs of C9orf72-ALS patient iPSC lines (mC9-1, mC9-2, and mC9-3-MG) and their paired gene-edited isogenic controls (isoC9-1, isoC9-2, and isoC9-3-MG) (Fig. 1A and table S1) (11).