In addition to being the most common cause of ALS and FTD, two related neurodegenerative conditions [3], there is genetic evidence to suggest that the C9orf72 repeat expansion also contributes to Alzheimer’s disease [4–7], Huntington’s disease [8], and other neurological conditions, including multiple system atrophy [9], depressive pseudodementia [10], and bipolar disorder [11]. Here, C9orf72 is linked to amyotrophic lateral sclerosis.