On the contrary, HD and FTD are caused by expansion of simple repeats dominantly inherited CAG in exon 1 of the huntingtin gene and mutations in microtubule-associated protein tau (MAPT), progranulin (PGRN), and chromosome 9 open reading frame 72 (C9orf72) expansion mutations, respectively [103,104]. Here, GRN is linked to Huntington disease.