As elements go, iron is a fickle and mischievous companion. Essential to life, yet impulsive, promiscuous, and destructive when allowed to roam unescorted, it poses a tremendous engineering challenge to human tissues.

Iron readily exchanges electrons with other elements. Indispensable to oxygen transport and metabolism, this property may also cause disease if iron participates in unsanctioned electron exchanges that produce free radicals -- an evanescent and particularly hot-blooded family of compounds that damage cells and DNA. As a result, all organisms dependent on iron -- from primitive bacteria to mammals -- go to great lengths to safely transport and store this potentially poisonous payload. Under normal conditions, this meticulously coordinated system functions beautifully. However, in those who absorb more iron than average, the extra influx eventually overwhelms this transport and storage system. Eventually, rogue iron escapes its minders and chemical mischief ensues.