PSEN1 and early-onset autosomal dominant Alzheimer disease: Alzheimer’s disease is the most common cause of dementia worldwide1 and is biologically defined by pathological accumulation of amyloid-β (Aβ) plaques and neurofibrillary tau tangles.2 Alzheimer’s disease can be either sporadic or due to dominantly inherited mutations in the genes Presinilin-1 (PSEN1), PSEN2 or Amyloid Precursor Protein (APP).