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. Here, C9orf72 is linked to early-onset autosomal dominant Alzheimer disease.