GSTM1 and Schnyder corneal dystrophy: Patients with SCD suffer from repeated bouts of ischemia/reperfusion injury resulting in intravascular hemolysis and release of xanthine oxidase (XO) from injured tissues.[15]–[17] As XO generates superoxide anion which dismutates into hydrogen peroxide and cell-free hemoglobin (cf Hb) can degrade hydrogen peroxide into hydroxyl radicals, [18] it is possible that plasma supernatants from SCD patients will contain these pro-oxidant components and therefore artificially increase p-HDL.