Genetic aspects of amyloid beta-protein fibrillogenesis in Alzheimer's disease.

Although deposition of aggregated amyloid beta-protein (Abeta) in human brain is a fundamental pathological event in the development of Alzheimer's disease (AD), our knowledge of the molecular mechanisms underlying the initiation of Abeta fibril formation remains still very incomplete. Recent data indicate that genetic factors have a direct effect on Abeta fibrillogenesis. Most of pathogenic mutations identified in genes responsible for familial AD (FAD) affect activities of alpha-, beta, and gamma-secretases during amyloid precursor protein (APP) processing leading to a significant increase in the Abeta42/Abeta40 concentration ratio. The enhanced anabolism of Abeta may lead to its deposition. Recently, it was shown that the two main alloforms of Abeta have distinct biological activity and behaviour at the earliest stage of assembly. In vitro studies showed that Abeta42 monomers, but not Abeta40, form initial and minimal structures (pentamer/hexamer units called paranuclei), which can oligomerise to larger forms. This finding may explain the particularly strong association of Abeta42 with AD. We have reviewed molecular effects of APP and Presenilin mutations responsible for FAD in both Abeta metabolism and formation of Abeta fibril.