C9orf72 and amyotrophic lateral sclerosis: Of these three, the C9orf72 repeat expansion is the most common3 and especially frequent in the Scandinavia and Northern Europe,1 causing the majority of familial FTD and amyotrophic lateral sclerosis (ALS) cases in Finland4 while GRN mutations are the most common genetic etiologies for FTD in Italy.5, 6