The white powder that arrived in envelopes addressed to lawmakers and journalists in 2001 proved to be a deadly delivery for several people. The lethal substance—spores commonly known as Anthrax (from the bacterium Bactillus anthracis)—can cause a toxic reaction in a host’s blood stream, killing cells and leading to tissue damage, bleeding and death. But just how toxic anthrax is to an individual might depend on their genetic makeup, according to a new study, published online Monday in Proceedings...