Therefore, in this Italian retrospective cohort study, we aimed to analyze the phenotypic characteristics of the main forms of genetic Alzheimer’s Disease and Frontotemporal Dementia, including age at onset, as well as examining the effect of mutation type (APP, PSEN1, PSEN2, MAPT, GRN, and C9orf72 genes). The gene discussed is PSEN1; the disease is frontotemporal dementia.