I don't have any experience with this directly, so I'm asking you all. Can those who suffer from dementia see it coming? I ask because I suspect I'm going out this way. I just want to know if I can tell when it's onset so I can punch my own ticket and be done with it.
Usually, people with dementia, any kind, know that something is wrong with them, with one exception and that is frontotemporal dementia. One characteristic of it is that people who have it are unaware that anything is wrong with them, which may seem great for them but not so great for those around them.
I know a woman who, before putting her husband in a nursing home, had to (among other things) bail him out of jail a couple times because he was peeking in the neighbors' windows, something he NEVER did before.
Robin Williams' LBD was not diagnosed until his autopsy; I had heard that he had "symptoms of Parkinson's" and LBD is indeed like a cross between Alzheimer's and Parkinson's, and worse than either. One of the most cruel things about LBD is that people who have it can live in the final, terminal phase for incredibly long periods of time, as in 10 years or more. He really did himself and his family a favor by choosing to end his life; I have never, since hearing he had LBD, considered his death to be a suicide.
Having Alzheimers before being middle aged is extremely unfortunate. Could you imagine being born and then growing up you find your mother doesn't recognize you? I heard a story about a girl in China who get dementia when she was 17. It's a very eerie feeling being older than a dementia patient. I wish the best for them. Dementia is an extremely cruel disease.
One wonders if the 31-year-old woman got extra copies of a bad gene. Huntington's usually strikes in middle age or later, but if the aberrant gene is "bigger" (see footnote), let's just say, the "bigger" the gene, the earlier the onset. My parents knew of a couple whose adopted daughter developed it in her late teens or early 20s. Thankfully, she did not have any children.
I also knew a woman whose daughter, as a teenager, developed Alzheimer's-like symptoms, and fortunately she saw the right doctors who had seen the rare autoimmune disorder she had, and it was treated and she made a near-complete recovery.
Footnote: The Huntington's gene is part of a set of repeating DNA codons, and if a person had >15 repeats, they WILL eventually get it. At 15 repeats, they will probably die before they have symptoms, or be misdiagnosed, but if they have repeats in the hundreds, it will strike much earlier. I worked, years ago, with a woman whose father was believed to have Alzheimer's until SHE got an HD diagnosis in her 40s! That was quite a devastating blow to everyone; she didn't have any children either. ETA: And she died in 2021! She lived with this nightmare for more than 15 years.