b–d Pie charts representing the percentage of APP, PSEN1, and PSEN2 mutations represented in the DIAN fibroblast bank (b), DIAN observational study (c), and reported in the Alzheimer’s disease (AD)/frontotemporal dementia (FTD) mutation database (d) [7]. The gene discussed is PSEN2; the disease is early-onset autosomal dominant Alzheimer disease.