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In Alzheimer's disease (AD) a variety of amyloid β-peptides (Aβ) are deposited in the form of extracellular diffuse and neuritic plaques (NP), as well as within the vasculature. The generation of Aβ from its precursor, the amyloid precursor protein (APP), is a highly complex procedure that involves subsequent proteolysis of APP by β- and γ- secretases. Brain accumulation of Aβ due to impaired Aβ degradation and/or altered ratios between the different Aβ species produced is believed to play a pivotal role in AD pathogenesis. While the presence of Aβ40 and Aβ42 in vascular and parenchymal amyloid have been subject of extensive studies, the deposition of carboxyterminal truncated Aβ peptides in AD has not received comparable attention. In the current study, we for the first time demonstrate the immunohistochemical localization of Aβ37 and Aβ39 in human sporadic AD (SAD). Our study further included the analysis of familial AD (FAD) cases carrying the APP mutations KM670/671NL, E693G and I716F, as well as a case of the PSEN1 Exon9 mutation. Aβ37 and Aβ39 were found to be widely distributed within the vasculature in the brains of the majority of studied SAD and FAD cases, the latter also presenting considerable amounts of Aβ37 containing NPs. In addition, both peptides were found to be present in extracellular plaques but only scarce within the vasculature in brains of a variety of transgenic AD mouse models. Taken together, our study indicates the importance of C-terminally truncated Aβ in sporadic and familial AD and raises questions about how these species are generated and regulated. [ABSTRACT FROM AUTHOR]