Using fluorescent in situ hybridization (FISH) coupled with immunocytochemistry, we analyzed the nuclei of these cells and observed colocalization between G4C2 RNA foci and MATR3 in two independent C9-ALS patient-derived iPSC-MNs (Fig. 1a) (Additional file 1: Figure S1A). The gene discussed is MATR3; the disease is amyotrophic lateral sclerosis.