It was found that deletion mutation in endothelin-converting enzyme 1 (ECE1) and endothelin-converting enzyme 2 (ECE2) increases amyloid β proteins that are Aβ (1-40) and Aβ (1-42) proved by the animal model (rat) of Alzheimer disease in addition to this increased level of ECE2 in the brain altogether indicates a clear pathway towards Alzheimer disease. Here, ECE2 is linked to early-onset autosomal dominant Alzheimer disease.