The most common form of Aβ produced by APP ends at amino acid position 40 (Aβ40, ~ 80–90%), whereas Aβ ending at position 42 (Aβ42, ~ 5–10%) has greater neurotoxicity and is thought to have a preferential role in the formation of AD-related amyloid plaques.13 AD amyloid plaques are formed from aggregated extracellular fibrils of Aβ and have been associated with cognitive impairment and dementia. The gene discussed is APP; the disease is Alzheimer disease.