C9orf72 and amyotrophic lateral sclerosis: We first compared the passive membrane properties of control MNs co‐cultured with astrocytes from a healthy individual (Con‐2), three ALS patients carrying the C9orf72 hexanucleotide repeat expansion (C9‐1, C9‐2, and C9‐3) as well as an isogenic control line for C9‐3 (C9‐Δ).