alt Hacker NewsPSA to those with family affected by dementia/Alzheimer's at a relatively early age (say <70yo): Get them tested for STDs, specifically Syphilis.
Left untreated for a very long time (decade+), it spreads to the brain and causes dementia among other things. Older generations with stigmas, taboos, or from lower educational backgrounds seem (to me) less likely to get tested, so it seems plausible.
Source: Have recently discovered this myself with a family member from their neurologist.
Lenin famously died from it, you could see that obscure blank stare of a crazy person on his later photos