C9orf72 and frontotemporal dementia: Volumetric MRI studies of genetic FTD have particularly highlighted the importance of subcortical structures in the pathogenesis of FTD, and more recent work using novel postprocessing techniques has aimed to study the subregions within these structures, e.g. there are differential patterns of atrophy within hippocampal subregions in the different genetic groups: MAPT mutation carriers had involvement of CA1-4, C9orf72 expansion carriers CA4, CA1 and the dentate gyrus, and GRN mutation carriers the presubiculum and subiculum [40].