C9orf72 and amyotrophic lateral sclerosis: Since the discovery of the chromosome 9 open reading frame 72 (C9orf72) repeat expansion mutation in 2011 as the most common genetic abnormality in amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig’s disease) and frontotemporal dementia (FTD), progress in understanding the signaling pathways related to this mutation can only be described as intriguing.