C9orf72 and amyotrophic lateral sclerosis: Eight studies (Lopez-Gonzalez et al., 2019; Maor-Nof et al., 2021; Lopez-Gonzalez et al., 2016; Andrade et al., 2020; Nihei et al., 2020; Pal et al., 2021; He et al., 2023; Marques et al., 2024) used iPSC-derived neuronal systems to investigate the consequences of repetitive protein sequence expansion on C9orf72-mediated ALS-FTD.