69 Although in the Adult Changes in Thought (ACT) and Nun Studies, nondemented seniors with severe AD pathology (mean age of 89.15±6.9 to 90.80±5.2

years) amounted to 8% and 12%, respectively, most of them showed neuritic Braak stage V, and frontal NFT counts were slightly lower than in a comparable dementia group.49 Moreover, review of clinical data from those studies revealed that most of the seniors classified as nondemented were indeed significantly memory-impaired.49 Inhibitors,research,lifescience,medical A recent study of nondemented elderly demonstrated 62% with low and 28% with high NFT levels70; 87 nondemented elderly (mean age 87 ±5.9 years; mean MMSE 28.3) showed mean Braak stage 3.0±0.9, a total NFT score of 4.5±2.5, and mean neuritic density of 1.3±1.1, whereas AD cases showed much higher cortical neuritic and striatal amyloid plaque scores.71 The 90+ study revealed significantly less severe Aβ, α-synuclein, and TPD-43 pathologies,

and hippocampal sclerosis in nondemented subjects, while Aβ distribution showed no essential differences; Inhibitors,research,lifescience,medical nondemented individuals had limited hippocampal tau and neocortical Aβ pathology.72 A recent clinicopathologic study of 296 persons without cognitive impairment of the Religious Inhibitors,research,lifescience,medical Order Study (ROS) and the Memory and Aging Project (MAP) showed a common presence of AD pathology and macroscopic infarctions. Amyloid load was related to global cognition (P<0.05), with only a trend for NFTs (P =0.08), while NFTs and macroscopic infarctions were related to episodic memory (P =0.03 Inhibitors,research,lifescience,medical and 0.02, respectively); AD pathology and Aβ load to working memory (P =0.02 and 0.03, respectively).73

Comparing the biochemistry of AD and nondemented nonagenerians revealed the lack of clear amyloid-related pathological/ biochemical determination between both groups.74 A personal retrospective study of 100 nondemented elderly (mean age 81.23±5.47 years, mean Mini Mental State Examination (MMSE) score 29) revealed negative Khachaturian criteria Inhibitors,research,lifescience,medical and CERAD stage 0 in 83% and 86%, respectively, only 13% with CERAD stage A and 1% stage B. Braak neuritic stages ranged from 0 to IV with an average score of 2.3±0.8. 12% were scored NIA-RI low, and only 2% intermediate likelihood for AD.37 Thus, mounting evidence from clinicopathologic studies support the view Isotretinoin that AD is a continuous spectrum between asymptomatic lesions in cognitively normal elderly and dementia, with mild cognitive impairment (MCI) as a transition phase between them.75 Although correlations between cognitive check details deficits and the severity and extension of senile plaques (SP) and NFTs (see ref 42) have been found, at least in those brains without other pathologies, the distinction between “physiological” (in nondemented subjects) and “pathological” aging (PA) is difficult.