GAP43 and Alzheimer disease: The biological variance in PC 1 was not associated with the clinical diagnosis despite levels of some of these intercorrelated proteins, such as GAP43, AMPH, PTPRN2 and SNCB, having been observed to be different between diagnostic and/or ATN groups.14,17 Since we in our analyses observed that low PC 1 values were strongly related to a T+ category, we explored whether Alzheimer’s disease biomarker levels could account for a combined influence on PC 1.