Compared to age-similar controls, participants with Y-DM had significantly lower plasma Aβ40 (median [IQR]; 55.6 [45.2, 74.6] pg/mL vs. 97.8 [78.3, 108.3] pg/mL), Aβ42 (4.7 [3.8, 5.5] pg/mL vs. 7.4 [5.9, 8.6] pg/mL), and GFAP (45.5 [30.9, 68.8] pg/mL vs. 55.1 [45.4, 81.2] pg/mL), and higher pTau181 (1.7 [0.7, 4.1] pg/mL vs. 1.2 [0.9, 1.9] pg/mL) in adolescence (p < 0.05 for all). Here, GFAP is linked to diabetes mellitus.