This is often the situation for people at risk for C9orf72 repeat expansion-related clinical syndromes, underscoring the carrier community's desire that the scientific community shift towards a biological definition of C9orf72 disease (rather than C9-ALS or C9-FTD) and that the ALS and FTD communities work together to prevent all phenotypic manifestations of C9orf72 disease. This evidence concerns the gene C9orf72 and amyotrophic lateral sclerosis.