Representative mass spectra. (a) Representative mass spectra from an AD patient displaying the Aβ-isoform pattern before treatment (red spectra) and after treatment with 140 mg of the γ-secretase inhibitor LY450139 (blue spectra). The mass spectrometric signal of Aβ1-14/15/16 increased, whereas Aβ1-34 decreased. The longer isoforms, including Aβ1-17, Aβ1-40, and Aβ1-42, were unaffected by the treatment. The relative change as a response to treatment is displayed for (b) all Aβ isoforms detected in all samples and (c) α-sAPP and β-sAPP. The error bars represent standard errors of the mean.