Great article about early diagnosis of Parkinson's and eventually Alzheimer's. There is a woman who has synesthesia -- in her case, when she smells something, she also sees colors -- and she can smell Parkinson's and Alzheimer's before the person is really symptomatic. They're trying to develop a test that can do what she does, by identifying the specific compounds she's smelling, and then using a sample from a patient to see if they are producing those compounds.

https://www.spiegel.de/international/zeitgeis...95601.html