APP and Alzheimer disease: In Alzheimer’s disease, a small number of cases (<5%) are due to autosomal dominant early-onset Alzheimer’s disease, for which there are a number of rare, large-effect-size genetic variants that contribute to the pathology.16 These include mutations that result in abnormal protein products of amyloid precursor protein, or in the genes that code for the enzymes that alter the breakdown of amyloid precursor protein, both of which may result in an increase in amyloid plaques.