It's hard to know, but it's a worry. My mother didn't get dementia and as far as I know, her siblings didn't. I don't know about her parents. Her mother died in an air raid.
I never met one relative of my dead beat father. I've been isolated and afraid a lot in my life. I keep my brain going with reading, crafts, the cats. I wonder, but I actually know, that my mother never cared one bit how the isolation she forced on me would affect me during my life. What any of anything will do to me in older age, I don't know. I'll still be alone. That I know.