C9orf72 and frontotemporal dementia: Expansions of 30–7950 GGGGCC repeats in the C9orf72 gene, which resides in 9p21 (C9orf72Exp), are the most common cause of amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD) and numerous seemingly unrelated diseases including inflammation dysregulation, autoimmune diseases, over-expression of type I IFN genes (1–6) and melanoma (7).