A longitudinal study also reported CBF alterations in presymptomatic FTD patients (individuals with MAPT or GRN mutations) independent of GM atrophy, in which individuals with the greatest decrease developed symptoms during the follow-up, thus indicating that perfusion deficits may exist at the presymptomatic stage of the disease before substantial atrophy is present (51). The gene discussed is MAPT; the disease is frontotemporal dementia.