Oh man, was that a kick in the guts when I got to that bit. My Dad was diagnosed with that in the past year, (after obviously struggling for a while), and declined rapidly. He had a different variant, and indeed the one thing that DIDN'T change was his personality. In fact, that's what kind of fooled me for a while. He would still trot out his usual bad jokes and regular phrases, but after a while you realize these are almost like reflexes, and often wouldn't really make sense in context.
It was interesting to see for Lee how this seemed amplified after heart surgery. My Dad had really bad "post-operative delirium" for about a month after major heart surgery, and while he recovered somewhat, that was definitely the start of his major decline.
Sadly, after moving into a care facility in mid-March, within a couple weeks he was in hospital after contracting Covid-19. He passed away on the 4th of this month from it. The only good to come out of all this was that I'd visited him many times over the past couple years and said "goodbye" many times thinking it might be the last time, even if just mentally and not physically, I'd get to see "my Dad", as I knew him.
Apparently it is often a genetic disorder that can be hereditary, and you can get tested for the genetic markers. As a coder/manager myself who depends on my mind for work, and enjoys being mentally challenged and active, (and I also have young kids), something like this scares the crap out of me. I'm not sure I want to know if I might have it. For one thing, being in the U.S. healthcare system, if I did have the markers, would that then count as a "pre-existing condition" I'd have to disclose?