C9orf72 and amyotrophic lateral sclerosis: One of the most common genetic causes for both ALS and frontotemporal dementia (FTD), a closely related neurodegenerative condition that shares both genetic and pathological signs with ALS, is a GGGGCC hexanucleotide repeat expansion (HRE) in the C9ORF72 gene (C9-ALS) [2].