However, within the last decade, the hexanucleotide GGGGCC repeat expansion in the C9orf72 gene was identified as the most frequent cause of both ALS and FTD in Europe and North America,1,2 with up to 10% of cases identified in the combined presentation of FTD-ALS.3,4C9orf72 related FTD-ALS is an autosomal dominant disorder, with a 50% recurrence risk in first degree relatives. Here, C9orf72 is linked to amyotrophic lateral sclerosis.