FAD includes autosomal dominant Alzheimer’s disease (ADAD), carrying known causative gene mutation including the amyloid precursor protein (APP), presenilin 1 (PS1), or presenilin 2 (PS2) that are nearly 100% certain to show sequential pre-dementia and dementia stage clinical features and thus can be diagnosed before symptoms onset. The gene discussed is PSEN2; the disease is familial Alzheimer disease.