An overview of the literature reveals several aspects of heme biology: (i) it has a dualistic nature being an inducer of inflammation and tissue damage as well as cytoprotective via HO-1; (ii) it is difficult to quantify it in vivo; and (iii) its toxic properties are strongly amplified in presence of additional stimuli, such as infection, inflammation, or the presence of mutations for example in Hb or complement genes which occur, respectively, in SCD and aHUS. The gene discussed is GSTM1; the disease is Schnyder corneal dystrophy.