C9orf72 and amyotrophic lateral sclerosis: Aggregating poly(glycine-alanine) (poly-GA) is derivedfrom theunconventional translation of the pathogenic intronic hexanucleotiderepeat expansion in the C9orf72 gene, which is themost common genetic cause of frontotemporal dementia (FTD) and amyotrophiclateral sclerosis (ALS).