I posted some links on ApoE gene polymorphism in this thread (and this one). The ApoE4 allele, which increases in frequency from south to north Europe, results in the enzymes which are the weakest internal mercury chelators from the brain (ApoE3 is better, ApoE2 is the best but very rare in Europe). Interestingly, ApoE4 is also associated with the highest intelligence (ApoE2 with lowest) at younger and middle age, but also the highest rates of psychoses and faster mental decline with aging. The ApoE3+E3 or E3+E4 combo may be the best to have on balance.

This is of interest when considering studies measuring the effects of amalgams on humans -- if you pick younger to middle-age subjects, you won't see damage to IQ since ApoE4 who would be damaged the most would have higher IQ (on average) to start with, hence mercury would merely cause IQ spread to narrow, pushing the ApoE4 down toward ApoE3 and ApoE2 (who would be much less damaged). This masking effect of the ApoE polymorphism & IQ association would be most pronounced for tests on children (which is how the recent pro-amalgam studies were done; they also picked southern Europe, such Portugal, or for USA the non-European minorities, which would have the max frequency of ApoE3 and ApeE2 in Europe, hence it would have the least mercury sensitive population -- all choices clearly selected on purpose into the design of studies to whitewash the toxicity). See also a critique of a 2003 pro-amalgam study on adults, which used a different statistical trick.

Google scholar and regular google on ApoE+allele+mercury will give you lots of good hits. If you add countries in search terms (you can remove mercury for that search), you can get what your ancestors likely have (in my case it is 96% ApoE3, thus not too bad odds). You get from each of your parents one ApoE allele copy, yielding thus 6 possible pairs you could have: ApoE4+4, 4+3, 4+2, 3+3, 3+2, 2+2.

Keep in mind though, that present science is still extremely primitive in these matters of very subtle biochemistry. ApoE polymorphism is certainly one bit of the puzzle identified so far, but the largest part of this story is still a mystery. Tune in and listen carefuly to your own biochemical networks, which are far smarter in this realm than all the doctors & scientists in the world put together.