In the MCI-AD group, those with the shortest duration of symptoms had significantly higher mean α-synuclein CSF concentration (802.2 pg/mL, confidence interval: 553.9 - 1051.5 pg/mL) than patients in the group with longer duration (442.8 pg/mL, confidence interval: 320.3 - 565.4 pg/mL), two sample t-test, p = 0.01, extreme value at baseline excluded. This evidence concerns the gene SNCA and Alzheimer disease.