It is always good when someone mentions MLC. Even if, at least now, if one googles MLC there will be many articles about it. However I thing most of them confuse midlife transition with MLC. Or, at least, few address the type of MLC we deal with.
Robert Sapolsky does talk a lot about it, but like Kikki said, he never really explains what he believes it to be.
Yes, I think it is possible for untreated depression (or at least some kinds of depression) to lead to dementia.
My wife is dyslexic and I wonder how much that has contributed to her MLC if only because of the damage it would have done to her self-esteem. When we were in school she would have just been considered stupid. Pair that with a physically and emotionally abusive father and I think the stage is set for midlife problems due in part to a traumatic childhood.
Those could be contributing factors. But I'm not convinced that childhood issues alone are the cause of MLC. Many people have terrible childhoods and never have MLC. Others have nice, or ok childhoods and have MLC. Kikki will say that it depends of how the adults handled the trauma the child suffered.
For me the thing is, unless with the obvious things that are considered trauma, abuse (the case with your wife), rape, a violent accident, etc, it is impossible to know what each child will consider trauma. So, it really is not possible for the adults to respond if they do not identify something being a trauma for the child.
I still think excessive stress (the cortisol induced one) and all it causes, is, if not the one cause, one of the main causes of MLC. Depression probably follows stress. Then it all becomes a giant mess.
MBIB, given your wife's age, it is possible that her dyslexia had also contributed to her lack of self-esteem. I'm dyslexic, but mine is very mild. I was a bright kid, so, it pretty much passed unnoticed (it only tends to show when I'm very tired. I will write "write" instead of "right", will change the order of the letters in some words, etc). My younger sister is also dyslexic. She is 15 years younger than I am, and when she was a child it was severe. She had special classes (when she attended school teachers and parents were all already alert for the needs of dyslexic children), but, unlike for me, languages remain very challenging for her.
I've split the previous thread and put the links to the former one as well as the ones to the other neuroscience/neurochemistry threads on the bottom of the first post of this thread.
Sometimes good things fall apart so better things can fall together. (Marilyn Monroe)