The deposition of β-amyloid within the entorhinal cortex (EC) may play a key role in the development of mild cognitive impairment (MCI) in the elderly. To examine the relationship of β-amyloid deposition to MCI, EC tissue immunostained for this protein was quantitated from a cohort of aged Catholic religious clergy with a clinical diagnosis of MCI and compared to those with no cognitive impairment (NCI) and Alzheimer's disease (AD). β- amyloid staining was seen in 12 of the 20 NCI, in 10 of 12 MCI, and in all 12 AD cases within the EC. β-amyloid immunoreactivity displayed two patterns within the EC: (1) a crescent-shaped band within layers 3-4 or (2) bilaminar staining mainly within layers 2-3 and 5-6. Ten cases failed to display any detectable β-amyloid immunoreactivity. Despite the heterogeneity of β- amyloid loads within the clinical groups, decomposing an analysis of variance revealed a significant difference across groups in mean β-amyloid load within the EC based upon a linear trend analysis. Multiple comparisons testing revealed that NCI individuals had a significantly lower mean β- amyloid load (1.32) than AD individuals (4.55). The MCI individuals had a mean intermediate (2.60) load between NCI and AD, but not statistically distinguishable from the mean for either NCI or AD. Spearman rank correlation showed a trend for decreasing MMSE with increasing amyloid load that failed to reach statistical significance. Since many NCI cases displayed β-amyloid loads equal to or greater than that seen in some MCI and some AD cases, it is mostly likely that deposition of this protein is not the sole pathogenic event underlying cognitive impairment in the elderly.
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