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). The gene discussed is C9; the disease is amyotrophic lateral sclerosis.