A Method for Diagnosing Alzheimer's Disease Based on Salivary Amyloid-ß Protein 42 Levels.

ABSTRACT

We have developed a non-invasive method of diagnosing Alzheimer's disease (AD), which can also predict the risk of its future onset. It is based on measuring salivary levels of amyloid-ß protein terminating at position 42 (Aß42). Brain deposits of this peptide are characteristic of AD. Biomarker studies indicate that such brain deposits commence a decade or more prior to clinical onset of the disease. We report here that Aß42 is produced in all peripheral organs tested, thus establishing the generality of its production. We used this information to develop simple and sensitive tests to determine salivary Aß42 levels. The levels were first stabilized by adding thioflavin S as an anti-aggregation agent and sodium azide as an anti-bacterial agent. We then quantitated the Aß42 in a series of samples with ELISA type tests. Control cases showed almost identical levels of salivary Aß42 regardless of sex or age. All AD cases secreted levels of Aß42 more than double those of controls. Individuals at elevated risk of developing AD secreted levels comparable to the AD cases. The results establish that salivary Aß42 levels can be used to diagnose AD as well as to predict the risk of its future onset.