title: The influence of diagnosis, intra- and inter-person variability on serum and plasma Abeta levels.
abstract: Evidence suggests that high peripheral beta-amyloid (Abeta)(1-40) levels and low ratios of Abeta(1-42)/Abeta(1-40) are associated with increased risk for Alzheimer's disease (AD). In this cross-sectional design, serum and plasma samples from 67 AD patients and 146 controls (similar in age and gender) were evaluated using Abeta(1-40) and Abeta(1-42) ELISA. Coefficient of variance was calculated for intra- and inter-person variability of Abeta(1-40) and Abeta(1-42). Abeta(1-40) correlated with age, MMSE and their Abeta(1-42)/Abeta(1-40) ratios (p<0.05). Significantly higher Abeta(1-40) levels were observed in AD patients than controls (p<0.05) but no difference was observed for Abeta(1-42) (p>0.05). Serum Abeta(1-42)/Abeta(1-40) ratios were also significantly lower in AD patients than controls (p<0.05). Lower intra-person than inter-person variability was observed for serum and plasma Abeta(1-40) and Abeta(1-42) and these were higher in controls than in AD patients. The intra-person variability of serum Abeta(1-40) did not influence the group differences observed between AD patients and controls. Significant interaction was observed between diagnosis and intra-person variability for serum Abeta(1-40) levels (p<0.05) and was supported by our finding of higher intra-person variability for serum Abeta(1-40) in controls (26.97%) than in AD patients (18.35%). We confirm the previously observed differences in blood Abeta levels between AD and control groups. In addition, we now report the presence of high intra- and inter-person variability possibly due to factors that influence peripheral Abeta levels and warrant further investigation before the potential use of Abeta as an AD biomarker can be fully exploited.
authors.affiliation: Roskamp Institute, 2040 Whitfield Avenue, Sarasota, FL 34243, United States. labdullah@rfdn.org
authors.forename: Laila
authors.initials: L
authors.lastname: Abdullah
authors.forename: Daniel
authors.initials: D
authors.lastname: Paris
authors.forename: Cheryl
authors.initials: C
authors.lastname: Luis
authors.forename: Amita
authors.initials: A
authors.lastname: Quadros
authors.forename: Julia
authors.initials: J
authors.lastname: Parrish
authors.forename: Luis
authors.initials: L
authors.lastname: Valdes
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Keegan
authors.forename: Venkatarajan
authors.initials: V
authors.lastname: Mathura
authors.forename: Fiona
authors.initials: F
authors.lastname: Crawford
authors.forename: Michael
authors.initials: M
authors.lastname: Mullan
mesh_terms: D000368:Aged; D000544:Alzheimer Disease / Q000097:blood* / Q000175:diagnosis* / Q000503:physiopathology; D016229:Amyloid beta-Peptides / Q000032:analysis / Q000097:blood*; D015415:Biomarkers / Q000032:analysis / Q000097:blood; D001798:Blood Proteins / Q000032:analysis; D001921:Brain / Q000378:metabolism* / Q000503:physiopathology; D003430:Cross-Sectional Studies; D003937:Diagnosis, Differential; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D014644:Genetic Variation / Q000502:physiology; D006801:Humans; D008297:Male; D010446:Peptide Fragments / Q000032:analysis / Q000097:blood*; D010949:Plasma / Q000378:metabolism; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity
chemical_list: D016229:Amyloid beta-Peptides; D015415:Biomarkers; D001798:Blood Proteins; D010446:Peptide Fragments; C078592:amyloid beta-protein (1-40); C075222:amyloid beta-protein (1-42)