@karanw Such an interesting question! A question back to you: what is your main reason for wanting to know? So far, there isn’t really something that can be done to prevent dementia. The best thing that you can do is to take proper care of yourself and enjoy life.
Dementia is such a scary thing for everyone involved. Maybe they’ll have a plan by the time you are old enough. My mother is 97 and completely with it. She is totally up on the latest news and even gives me a hard time because I don’t watch the news all day. Her mother and brother both had dementia in their older years.
If I had known 50 years ago that I would have this autoimmune disease in my brain, I would have had 50 years to think about it and worry. Instead, I’ve had a good life, traveled all around the world, had two sons and two grandchildren, and the kindest, nicest husband ever!
Just live your life and love every day! (I didn’t answer your question about is there a test. I’m sorry, I just don’t know)