While ALS and FTD are the major phenotypes linked to C9orf72 repeat expansions, several additional phenotypes are documented, including Alzheimer's disease, Parkinson’s disease, Huntington’s disease-like movement disorder and various psychiatric presentations.13 14 Inclusion of such phenotypes adds complexity to pedigree interpretations on account of the high population prevalence of some of these conditions. This evidence concerns the gene C9orf72 and Alzheimer disease.