Yeah it's very new discovery (2003): they observed that people with both genes apo-E-4 (those that make proteins that dont carry out mercury at all) are much more likely to get alzheimer, then they understood that is probably due to less ability to detox mercury.

These proteins (whose primary role is to take away cholesterol from the brain) come in 3 different varieties depending on your genes: with one cisteine molecule (that has a sulfur group that binds mercury), with two cisteine molecules or with none.

That would explain why some people are damaged by mercury more than others.

You can search google to find stuff on this.

Another very interesting article by a toxicologist whose son got autism, that also talks about this and other stuff:

http://www.bioprobe.com/ReadNews.asp?article=82