C9orf72 and amyotrophic lateral sclerosis: We have recently established isogenic lines of iPSC-derived spinal MNs comprising parental C9ORF72 from ALS patients along with a (i) gene-corrected (GC) variant with intronic HREs excised, (ii) a KO of the exonic C9ORF72 part with intronic HREs maintained, and (iii) a similar KO of C9ORF72 in control cells with naturally no HREs (Abo-Rady et al, 2020).