The discovery of a hexanucleotide repeat expansion in the chromosome 9 open reading frame 72 (C9orf72) gene as the most common genetic cause of FTD and amyotrophic lateral sclerosis (ALS)—often referred to as c9FTD/ALS—stoked interest in the cerebellum. This evidence concerns the gene C9orf72 and amyotrophic lateral sclerosis.