• Aβ42 is elevated in plasma in FAD MCs and suggests that this level may decrease with disease progression prior to the development of overt dementia. • The ratio of Aβ42 to Aβ40 was reduced in the CSF of non-demented MCs and that elevations of t-tau and p-tau181 are sensitive indicators of presymptomatic disease. • Elevated F2-isoprostane levels in the CSF of preclinical FAD MCs suggests that oxidative stress occurs downstream to metabolism of amyloid precursor protein. Here, APP is linked to dementia.