JAM2 and Alzheimer disease: AD, Aβ+ MCI, and Aβ- MCI patients all showed decreases of three proteins in plasma, including RGMB (d = − 0.25 in Aβ- MCI; d = − 0.19 in Aβ+ MCI; d = − 0.12 in AD; q < 0.05), JAM-B (d = − 0.23 in Aβ- MCI; d = − 0.21 in Aβ+ MCI; d = − 0.17 in AD; q < 0.001), TRAIL (d = − 0.2 in Aβ- MCI; d = − 0.16 in Aβ+ MCI; d = − 0.17 in AD; q < 0.05).