C9orf72 and frontotemporal dementia: Several studies, including our own, show that hypermethylation of the CpG-island at the 5′ end of the repeat contributes to C9orf72 repression in a high of C9orf72-HRE carriers, yet down-regulation of C9orf72 is more prevalent and shown among FTD sporadic patients [19] and MAPT and GRN mutation carriers (this study).