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Amyloid β-peptide (Aβ) biosynthesis, aggregation and degradation constitute three important steps to consider in the study of pathological mechanisms involved in Alzheimer's disease (AD). Several proteins have been suggested as involved in each of these processes: proteolytic cleavage of the amyloid precursor protein by the β-site APP cleaving enzyme (BACE), increased amyloid fibril formation by the activity of the acetylcholinesterase (ACHE gene), and degradation of Aβ aggregates by the plasmin system have been exhaustively documented.A case-control design was used to evaluate the possible association between candidate genes involved in these three processes and AD. We analysed three polymorphisms located at the BACE1 gene, one polymorphism at the ACHE gene, and two variants located at the tissue plasminogen activator and plasminogen activator inhibitor-1 (genes TPA and PAI- 1, respectively), both part of the plasmin system.We found an association between BACE1 exon 5 GG genotype and AD (ageand gender-adjusted odds ratio = 2.14, P =0.014). Although a similar association was reported previously by Nowotny and collaborators only in subjects carrying the ε4-allele of the apolipoprotein E gene (APOE), we did not detect this effect. However,when we combined our results with those previously reported, a clear increase of the risk to develop AD appeared in subjects carrying both the BACE1 exon 5 GG genotype and the APOE ε4-allele (crude OR = 2.2, P = 0.004).These data suggest a possible genetic relation between BACE1 and AD.