C9orf72 and amyotrophic lateral sclerosis: In one, induced motor neurons (iMNs) derived from iPSCs of Amyotrophic lateral sclerosis/Frontotemporal dementia (ALS/FTD) patients with a C9orf72 repeat expansion revealed a haploinsufficiency of protein function resulting from the intronic expansion and deficiencies in motor neuron vesicular trafficking and lysosomal biogenesis that were not previously obvious in knockout mouse models.