GRN and behavioral variant of frontotemporal dementia: According to the results of the included studies, it can be concluded that among the investigated predictive variables, the occurrence of GRN genetic mutation or C9orf72 expansion, the predominance of frontal and frontotemporal anatomic patterns of atrophy, the presence of elevated serum neurofilament light chain (NfL) levels, the magnitude of dysfunction of inhibitory and facilitatory intracortical circuits, as well as the severity of executive deficits and apathy emerge as robust correlates of functional impairment in individuals diagnosed with bvFTD.