I have noted that at least one of my sons and I both have the GT version of the rs8177822 snp. It looks like not more than about 5% of the population have this, and it looks as if no one or very few are homogeneous (TT). GG is the wild type, which appears to be 95% of the population. This gene is for the enzyme which catalyses the second step in the pathway to make heme. This enzyme is especially vulnerable to lead. Do any of you have this mutation?