C9orf72 and frontotemporal dementia: Up to 15% of people with ALS develop FTD1 and a similar proportion of people with FTD develop ALS.2 3 Similarities in profile of cognitive impairment have been identified in the two disorders, although more severe in FTD.4 TDP-43 pathology occurs in both conditions.5 So too do expansions in the C9ORF72 gene.6–9 Such convergent evidence supports the notion of a spectrum or continuum of disease.3 10