The molecular link between ALS and FTD has been confirmed by the discovery of the hexanucleotide repeat expansions in the 3′ untranslated region of the chromosome 9 open reading frame 72 gene (C9orf72, OMIM 614260), the most common known monogenetic cause of both ALS and FTD.5,6,7. The gene discussed is C9orf72; the disease is amyotrophic lateral sclerosis.