C9orf72 and dementia: reported cross‐sectional atrophy in presymptomatic and symptomatic carriers of mutations in MAPT, GRN, or C9orf72. In relation to estimated year of onset of dementia, there was early volume loss of the insula and temporal lobe (∼10 years before expected symptoms onset), followed by the frontal lobe and subcortical structures (∼5 years before expected onset), parietal and cingulate gyrus (around time of expected onset), and occipital lobe (∼5 years after expected onset).