C9orf72 and Mental deterioration: These results complement recent studies showing cognitive decline in the early stages of FTD with widespread cognitive impairment covering multiple domains in C9orf72 [22, 43], dysexecutive functioning as the key feature in GRN [13, 22] and a specific impairment in episodic and semantic memory in MAPT-associated FTD [13, 20, 22].