Alzheimer Disease Alzheimer disease Alzheimer’s disease Amyloid beta-Peptides Article Cognitive Dysfunction Dementia Disease Progression Humans Mild cognitive impairment Plasma biomarkers aged amnesia amyloid beta protein amyloid beta protein[1-40] amyloid beta protein[1-42] brain size cognition cognitive defect disease exacerbation female genetics genotype glial fibrillary acidic protein human major clinical study male metabolism neurofilament protein p-tau