C9orf72 and amyotrophic lateral sclerosis: In ALS/FTD Human Induced Motor Neurons (iMNs), C9orf72 haploinsufficiency may increase glutamate receptors on the surface of iMNs, leading to excitotoxicity and impaired clearance of DPRs, leading to neurotoxicity, ultimately resulting in neurodegeneration (Shi et al., 2018).