A blood-prick test for Alzheimet's using tau markers. This test is promoted beneficial because it would allow early start to treatment for the disease—and every pharmacological intervention available so far is effective only in early stages of disease progession.
But I can attest that it would be far more significant for early-onset Alzheimer's. My partner had weird behavioral changes starting in her early 50s. Her medical and mental health health providers assumed she was just crazy (in a nutshell). They went through half the DSM-IV-R and DSM-V with fancy labels about what was wrong, drugs to match, talk-therapy programs where she was blamed for "not trying hard enough."
And all the time they were barking up the wrong tree, wasting buckets of time and money, and making everyone involved miserable.
A simple blood test. Shaking my head.