Each of the tryptic peptide assays of synaptotagmin-1 (215–223 and 238–245) could differentiate MCI due to Alzheimer’s disease from controls in both sample sets, with area under the curve of 0.988 (0.952–1.025) (P = 0.001) and 1.000 (1.000–1.000) (P = 0.0009) (sample set I), respectively, and of 0.813 (0.692–0.934) (P = 0.0002) and 0.801 (0.676–0.926) (P = 0.0003) (sample set II), respectively (Fig. 2a). Here, SYT1 is linked to early-onset autosomal dominant Alzheimer disease.