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

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-beta protein terminating at position 42 (A beta(42)). 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 A beta(42) 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 A beta(42) 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 A beta(42) in a series of samples with ELISA type tests. Control cases showed almost identical levels of salivary A beta(42) regardless of sex or age. All AD cases secreted levels of A beta(42) 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 A beta(42) levels can be used to diagnose AD as well as to predict the risk of its future onset.