These neuroanatomical correlates are in line with the predominant frontal involvement in GRN mutation carriers [6, 34], and link the degradation of the fronto-insula network to less cognitive flexibility—and as a consequence early clustering-switching impairment—as the most likely underpinning of declining fluency performance in conversion to GRN-associated FTD. The gene discussed is GRN; the disease is frontotemporal dementia.