C3 and Alzheimer disease: Among all the potential markers proposed, Aβ42, which has a significant role in Aβ pathology, brain-derived neurotrophic factor (BDNF), which may have a role in cognitive dysfunctions in AD, and complement C3, which has been reported as a marker of brain atrophy in AD and amyloidosis in non-demented elderly, were the most repeated in the panels (Table 5).