C9orf72 and amyotrophic lateral sclerosis: In 2011, independent research groups made a groundbreaking discovery and were able to ascribe over 30-55% of fALS, 20-25% of fFTD and actually the majority of familial ALS/FTD cases to “GGGGCC” hexanucleotide repeat expansions (HREs) in the 5’ non-coding sequence of the C9orf72 gene, making it the most common genetic cause of ALS/FTD [248-250].