This is one thing I used to fear very much. I have seen it in people fairly close to me (not direct family members but close enough to really disturb me) and it is sad beyond words.
@galenkp take the time to research more about autophagy .... it is for me the answer to the question 'What can I do to ensure that I do not develop dementia or alzheimers?' .... I have modified my lifestyle starting almost a year ago to encourage autophagy in my body and I can really feel the benefits. I feel mentally sharper,and just all round healthier!!