Analyses of postmortem brain tissues of C9ALS/FTD patients, as well as of patient-derived cultured cells, have led to proposed mechanisms whereby C9ORF72 repeat expansions cause the diseases; these include loss of C9ORF72 function (i.e., haploinsufficiency) and gain-of-toxicity from repeat-containing RNAs and aberrant dipeptide-repeat (DPR) proteins, through repeat-associated non-AUG-dependent (RAN) translation [4, 5, 9, 10]. This evidence concerns the gene C9orf72 and frontotemporal dementia.