I post on Alzheimers research as it is a dementia and there are common links in some cases.  This article I read said not as many African American’s had been surveyed as European’s but they found when they looked at DNA from 6,000 there is a gene ABCA7, which had a strong link to Alzheimers and subjects who had changes to that location were 1.8 times more likely to have Alzheimer’s disease than people without the changes.  The effect was about 60 percent stronger in African American’s than in subjects of European descent, according to the team.